131554606-Flow-Control

Flow Control RAN12.0

Feature Parameter Description

Issue 04

Date 2011-09-30

HUAWEI TECHNOLOGIES CO., LTD.

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WCDMA RAN

Flow Control Contents

Issue 04 (2011-09-30) Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd

i

Contents

1 Introduction ................................................................................................................................ 1-1

1.1 Scope ............................................................................................................................................ 1-1

1.2 Intended Audience ........................................................................................................................ 1-1

1.3 Change History .............................................................................................................................. 1-1

2 Overview ..................................................................................................................................... 2-1

2.1 Definition ....................................................................................................................................... 2-1

2.2 Overall Picture of Flow Control ..................................................................................................... 2-1

3 Flow Control for Overloaded RNC Units............................................................................. 3-1

3.1 Principle ......................................................................................................................................... 3-1

3.1.1 Overview ............................................................................................................................... 3-1

3.1.2 CPU Usage Monitoring ......................................................................................................... 3-2

3.1.3 Message Block Occupancy Rate Monitoring ........................................................................ 3-2

3.2 Whole Picture of Flow Control for Overloaded RNC Units ............................................................ 3-2

3.3 Flow Control Triggered by CPUS Overload .................................................................................. 3-5

3.3.1 Overview ............................................................................................................................... 3-5

3.3.2 CPUS Basic Flow Control..................................................................................................... 3-5

3.3.3 Access Control ...................................................................................................................... 3-6

3.3.4 Paging Control ...................................................................................................................... 3-8

3.3.5 RRC Flow Control ................................................................................................................. 3-9

3.3.6 Flow Control on Signaling Messages over the Iur Interface............................................... 3-10

3.3.7 CBS Flow Control ................................................................................................................3-11

3.3.8 Cell/URA Update Flow Control ............................................................................................3-11

3.3.9 Flow Control over the Iur-g Interface .................................................................................. 3-12

3.3.10 Queue-based RRC Shaping ............................................................................................. 3-13

3.4 Flow Control Triggered by MPU Overload .................................................................................. 3-14

3.4.1 Basic Flow Control for the MPU ......................................................................................... 3-14

3.4.2 MPU Overload Backpressure ............................................................................................. 3-15

3.5 Flow Control Triggered by INT Overload ..................................................................................... 3-17

3.5.1 INT Basic Flow Control ....................................................................................................... 3-17

3.5.2 Flow Control Triggered by INT Overload on the Control Plane .......................................... 3-17

3.5.3 Flow Control Triggered by Iub Interface Board Overload on the User Plane ..................... 3-18

3.6 Flow Control Triggered by DPU Overload ................................................................................... 3-18

3.6.1 DPU Basic Flow Control ..................................................................................................... 3-18

3.6.2 Flow Control Triggered by DSP CPU Overload .................................................................. 3-19

3.7 Flow Control Triggered by SCU Overload ................................................................................... 3-19

3.7.1 Principle .............................................................................................................................. 3-19

3.7.2 Overload Indication ............................................................................................................. 3-20

3.8 Flow Control Triggered by GCU Overload .................................................................................. 3-20

3.8.1 Principle .............................................................................................................................. 3-20

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3.8.2 Overload Indication ............................................................................................................. 3-20

4 Flow Control Triggered by NodeB/Cell Overload ............................................................. 4-1

4.1 CAPS Control ................................................................................................................................ 4-1

4.1.1 Principle ................................................................................................................................ 4-1

4.1.2 Overload Indication ............................................................................................................... 4-3

4.2 PCH Congestion Control ............................................................................................................... 4-3

4.2.1 Principle ................................................................................................................................ 4-3

4.2.2 Overload Indication ............................................................................................................... 4-4

4.3 FACH Congestion Control ............................................................................................................. 4-4

4.3.1 Overview ............................................................................................................................... 4-4

4.3.2 Flow Control Based on Limited Number of UEs in the CELL_FACH State .......................... 4-5

4.3.3 CCCH Flow Control .............................................................................................................. 4-7

4.3.4 DCCH Flow Control .............................................................................................................. 4-8

5 Flow Control over the Iu Interface ........................................................................................ 5-1

5.1 SCCP Flow Control ....................................................................................................................... 5-1

5.1.1 Overview ............................................................................................................................... 5-1

5.1.2 Flow Control Based on Iu Signaling Load ............................................................................ 5-2

5.1.3 Flow Control Based on SCCP Setup Success Rate ............................................................ 5-2

5.1.4 CN SCCP Congestion Control ............................................................................................. 5-3

5.2 Flow Control Triggered by CN RANAP Overload .......................................................................... 5-3

6 Service Flow Control ............................................................................................................... 6-1

7 Load Sharing .............................................................................................................................. 7-1

7.1 Overview ....................................................................................................................................... 7-1

7.2 Load Sharing on the Control Plane ............................................................................................... 7-2

7.2.1 Procedure for Load Sharing on the Control Plane ............................................................... 7-2

7.2.2 Service Request Processing by a CPUS ............................................................................. 7-4

7.3 Load Sharing on the User Plane ................................................................................................... 7-6

7.3.1 Overview ............................................................................................................................... 7-6

7.3.2 Procedure for Load Sharing on the User Plane ................................................................... 7-6

8 Engineering Guidelines ........................................................................................................... 8-1

8.1 Access Control and Domain-Specific Access Control ................................................................... 8-1

8.1.1 Factors That Affect Access control and Domain-Specific Access Control ............................ 8-1

8.1.2 Configuration Principles and Suggestions............................................................................ 8-1

8.1.3 Performance Optimization .................................................................................................... 8-2

8.1.4 Key Parameter Settings........................................................................................................ 8-2

8.2 Queue-based RRC Shaping ......................................................................................................... 8-2

8.2.1 Factors That Affect Queue-based RRC Shaping ................................................................. 8-2


8.3 CAPS Control ................................................................................................................................ 8-2

8.3.1 Factors That Affect CAPS Control ........................................................................................ 8-2

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8.3.3 Performance Optimization .................................................................................................... 8-3

9 Parameters ................................................................................................................................. 9-1

10 Counters ................................................................................................................................. 10-1

11 Glossary .................................................................................................................................. 11-1

12 References ............................................................................................................................. 12-1

13 Appendix: Flow Control Algorithms ................................................................................ 13-1

13.1 Switch Algorithm ........................................................................................................................ 13-1

13.2 Linear Algorithm ........................................................................................................................ 13-1

13.3 Hierarchical Algorithm ............................................................................................................... 13-2

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Flow Control 1 Introduction



1-1

1 Introduction

1.1 Scope

This document concerns the feature WRFD-040100 Flow Control. It describes the functions and principles of RNC flow control, as well as the overload indications.

This document describes flow control for overloaded RNC units, flow control triggered by NodeB/cell overload, flow control over the Iu interface, and flow control on user services. The principles and overload indications are presented for each type of flow control function.

This document describes the principles of flow control. If you need specific overload control measures for mass gathering events, contact Huawei’s professional service teams, who can provide tailored solutions.

1.2 Intended Audience

This document is intended for:

Personnel who have a good understanding of WCDMA principles

Personnel who need to learn about flow control

Personnel who work on Huawei products

1.3 Change History

This section describes the change history of this document. There are two types of changes:

Feature change: refers to a change in the flow control feature of a specific product version.

Editorial change: refers to a change in wording or the addition of the information that was not described in the earlier version.

Document Issues

The document issues are as follows:

04 (2011-09-30)

03 (2010-10-15)

02 (2010-06-20)

01 (2010-03-30)

Draft (2009-12-05)

04 (2011-09-30)

Compared with issue 03 (2010-10-15) of RAN12.0, this issue incorporates the changes described in the following table:

Change Type Change Description Parameter Change

Feature change Added the description about FACH congestion control. For details, see 4.3 "FACH Congestion Control."

For changes in parameters, see related descriptions in the chapters.

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Flow Control 1 Introduction



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Change Type Change Description Parameter Change

Editorial change Optimized the entire document and added the following sections:

3.3.3 "Access Control"

3.3.4 "Paging Control"

3.3.5 "RRC Flow Control"

3.3.6 "Flow Control on Signaling Messages over the Iur Interface"

3.3.7 "CBS Flow Control"

3.3.8 "Cell/URA Update Flow Control"

3.3.9 "Flow Control over the Iur-g Interface"

3.4 "Flow Control Triggered by MPU Overload"

3.5.2 "Flow Control Triggered by INT Overload on the Control Plane"

3.6.2 "Flow Control Triggered by DSP CPU Overload"

4.2 "PCH Congestion Control"

8 "Engineering Guidelines"

For changes in parameters, see related descriptions in the chapters.

03 (2010-10-15)

This is the third commercial release of RAN12.0.

Compared with the 02 (2010-06-20), this issue optimizes the description.

02 (2010-06-20)

This is the second commercial release of RAN12.0.

The CAPS control and RRC shaping and queuing functions are introduced in this issue of RAN12.0. Descriptions of these features are added to section "CAPS Control" and "Queue-based RRC Shaping."

01 (2010-03-30)

This is the first commercial release of RAN12.0.

Compared with the draft (2009-12-05), this issue optimizes the description.

Draft (2009-12-05)

This is the draft of the document for RAN12.0.

Compared with issue 02 (2009-06-30) of RAN11.0, this issue optimizes the description

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Flow Control 2 Overview



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2 Overview

2.1 Definition

Flow control is a protective measure for communications between the RNC and its peer equipment. Flow control provides protection in the following ways:

It restricts incoming traffic to:

− Protect equipment from overload, thereby maintaining system stability.

− Ensure that equipment can properly process services even during heavy traffic.

It restricts outgoing traffic to reduce the load on the peer equipment.

2.2 Overall Picture of Flow Control

During mass gathering events, the amount of services surges, generating a significantly increased traffic volume that exceeds the processing capabilities of the system. As a result, the system becomes overloaded, which may lead to messages being randomly discarded and NE resetting, as well as response failures, call drops, service access failures, and other unexpected events.

Resources in a WCDMA system are limited, so how they are used affects system performance. The resources concerned here are:

Equipment system resources, including CPU resources and memory

Air interface resources, including channels, codes, and power

Transmission resources

Core network processing capabilities

To keep system stability and capabilities at the maximum possible level, Huawei RNCs perform flow control at five points in the system, which are numbered in Figure 2-1.

Figure 2-1 Five points in flow control

Flow control involves discarding originating messages (such as RRC connection requests) that overload the system when system resources are insufficient, refusing to process low-priority services, and rejecting access requests for low-priority services.

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Flow Control 2 Overview



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To address problems caused by limited RNC resources (labeled in Figure 2-1), the RNC performs flow control for RNC units. The software of each RNC board monitors the system resource usage. When necessary, the RNC starts basic flow control functions that suspend non-critical functions, such as recording logs and printing to reduce the system load. Then, based on the system load and the switch status of flow control functions, the RNC may perform other flow control functions to ensure system stability. For details, see chapter 3 "Flow Control for Overloaded RNC Units."

To address problems caused by limited air interface resources (labeled in Figure 2-1), the RNC performs CAPS control, PCH congestion control and FACH congestion control. When the NodeB or cell is overloaded with services, RNC limits the number of RRC connection requests admitted to a cell or NodeB each second. For details, see 4.1 "CAPS Control." When the paging channel is congested, the RNC allows CS-domain paging messages to preempt PS-domain paging messages in order to raise the paging success rate in the CS domain. For details, see section 4.2 "PCH Congestion Control." When the FACH is congested, the RNC restricts message retransmissions on the logical channels, rejects certain PS service requests, and triggers state transitions such as CELL_PCH to CELL_DCH (P2D) and CELL_DCH to idle (D2Idle). This gives priority to access requests for high-priority services such as CS services, keeps the cell update success rate high, and reduces call drops. For details, see section 4.3 "FACH Congestion Control."

The RNC performs admission control, load reshuffling, and overload control on code and power resources. For details about admission control, see the Call Admission Control Feature Parameter Description. For details about load reshuffling and overload control, see the Load Control Feature Parameter Description.

To address problems caused by limited signaling bandwidth over the Iu interface (labeled in Figure 2-1), the RNC works with the core network to perform flow control over the Iu interface. Based on link congestion conditions detected at the local end and congestion indications reported from the peer end, the RNC performs flow control on initial UE messages to reduce the signaling traffic over the Iu interface. This prevents severe congestion on the signaling link between the RNC and the core network and reduces the load on the core network when it is overloaded. For details, see chapter 5 "Flow Control over the Iu Interface."

To address problems caused by limited transmission resources over the Iub interface (labeled in Figure 2-1), the RNC performs NodeB-level Call Attempts Per Second (CAPS) control to restrict the number of RRC connection requests that arrive at the NodeB each second when the Network Control

Protocol (NCP) link is congested. This prevents signaling impacts from single NodeBs and maintains a stable traffic volume within the system. For details, see 4.1 "CAPS Control." In addition, the RNC supports user-plane congestion control over the Iub interface to restrict transmission rates when there is transmission congestion over the Iub interface. This prevents packet loss and makes more efficient use of the bandwidth. For details, see chapter 6 "Service Flow Control."

For access requests, the RNC supports load sharing within one subrack or between subracks on the user plane and control plane. This achieves dynamic sharing of resources, balancing the load among subracks and boards and improving service processing efficiency. For details, see chapter 7 "Load Sharing."

Call%20Admission%20Control.htm


Load%20Control.htm

Load%20Control.htm

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Flow Control 3 Flow Control for Overloaded RNC Units



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3 Flow Control for Overloaded RNC Units

3.1 Principle

3.1.1 Overview

Each RNC board monitors the following in real time to keep track of resource consumption:

CPU usage: The CPU resources of a board determine the processing capabilities of the board. All functions running on the board use CPU resources.

Message block occupancy rate: Message blocks are resources used to send and receive messages within the RNC.

When the CPU usage or message block occupancy rate of a board is high, the board processing capabilities may become insufficient. When this occurs, the board triggers flow control to ensure that basic functions can continue to run properly. Flow control based on message block occupancy rate is independent of flow control based on CPU usage. Related flow control functions will be triggered when either the message block occupancy rate or the CPU usage is excessively high. Generally, it is rare to run out of message blocks.

Figure 3-1 shows the flow control model that each board follows based on CPU usage and message block occupancy rate.

Figure 3-1 Flow control model

The XPUs, interface boards (collectively known as INTs), DPUs, SCUs and GCUs mentioned in this document are board types displayed on the LMT. An XPU comprises MPUs and CPUSs, which have the following functions:

An MPU manages resources on the user plane, control plane, and transport plane, informs MPUs in other subracks about the load on the current subrack, and makes decisions regarding load sharing.

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A CPUS processes services on the control plane.

For the detailed functions of each board, see the BSC6900 UMTS Hardware Description.

3.1.2 CPU Usage Monitoring

The system checks CPU usage in real time. If the CPU usage has reached the threshold for starting a flow control function that is based on the CPU usage and currently enabled, this function is started.

To prevent frequent flow control triggered by CPU usage fluctuations, the system also calculates the average CPU usage during a period of time that has just elapsed, and determines whether to perform flow control based on this CPU usage. The CPU usage values used to calculate the average CPU constitute a filter window, as shown in Figure 3-2.

Figure 3-2 Filter window for calculating the average CPU usage

3.1.3 Message Block Occupancy Rate Monitoring

Once it has allocated message blocks ten times, the system checks the message block occupancy rate. If the message block occupancy rate has reached the threshold for starting a flow control function that is based on the message block occupancy rate and currently enabled, this function is started.

To prevent frequent flow control triggered by message block occupancy rate fluctuations, the system also calculates the average message block occupancy rate. The message block occupancy rate values used to calculate the average message block occupancy rate constitutes a filter window, as shown in Figure 3-3.

Figure 3-3 Filter window for calculate the average message block occupancy rate

3.2 Whole Picture of Flow Control for Overloaded RNC Units

Table 3-1 provides a whole picture of flow control for overloaded RNC units.

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Table 3-1 Whole picture of flow control for overloaded RNC units

Overload Source Flow Control Function

Flow Control Object

Impact on Services

Controlling Command

CPUS High CPU usage or message block occupancy rate

Printing flow control

Printing No SET FCSW

Debugging flow control

Debugging

Performance monitoring flow control

Performance monitoring

Logging flow control

Logging

Resource audit flow control

Resource audit

Paging control Paging messages Yes SET FCSW

AC Users in AC0 to AC9

SET FCSW

RRC flow control RRC connection requests

None

High CPU usage

Queue-based RRC shaping

RRC connection requests

SET UCACALGOSWITCH

High CPU usage or message block occupancy rate

Flow control on signaling messages over the Iur interface

Some signaling messages over the Iur interface

SET FCSW

Flow control over the Iur-g interface

All messages over the Iur-g interface

CBS flow control All broadcast messages delivered by the CBC

Cell/URA update flow control

Some cell/URA update messages

MPU High CPU usage or message block occupancy rate


Printing None SET FCSW


Debugging


Logging

High CPU usage

MPU overload backpressure


Yes SET RRCTRLSWITCH

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Overload Source Flow Control Function

Flow Control Object

Impact on Services

Controlling Command

INT High CPU usage or message block occupancy rate




Debugging


Logging

High CPU usage

Flow control triggered by INT overload on the control plane


Yes SET TNSOFTPARA

Congestion in queues at the ports

Flow control triggered by Iub interface board overload on the user plane

BE service rates

DPU High CPU usage or message block occupancy rate




Debugging


Logging

High DSP CPU usage

Flow control triggered by DSP CPU overload

BE service rates Yes None

SCU High CPU usage or message block occupancy rate




Debugging

Performance monitoring flow control

Performance monitoring


Logging

GCU High CPU usage or message block occupancy rate




Debugging


Logging

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The filter windows for flow control functions configured by the SET FCSW command are configurable. The details are as follows:

For flow control decisions based on CPU usage, the SMWINDOW parameter of the SET FCCPUTHD command is used to configure the filter window.

For flow control decisions based on message block occupancy rate, the SMWINDOW parameter of the SET FCMSGQTHD command is used to configure the filter window.

For flow control functions configured by the SET FCSW command, the system also uses a fast judgment window to prevent the CPU usage and message block occupancy rate from rapidly rising to a high level. The details are as follows:

If all CPU usage values during this fast judgment window are greater than or equal to a critical threshold, all currently enabled flow control functions based on CPU usage are started. The FDWINDOW and CTHD parameters of the SET FCCPUTHD command are used to configure the fast judgment window and critical threshold, respectively. The value of SMWINDOW should be at least twice the value of FDWINDOW.

If the current message block occupancy rate value is greater than or equal to a critical threshold, all currently enabled flow control functions based on message block occupancy rate are started. The size of the fast judgment window for flow control based on the message block occupancy rate is 1. That is, the critical threshold decision does not use the filter mechanism. The CTHD parameter of the SET FCMSGQTHD command is used to configure the critical threshold.

When the FCSW parameter is set to OFF, all flow control functions configured by the SET FCSW command are disabled.

3.3 Flow Control Triggered by CPUS Overload

3.3.1 Overview

The CPUS software monitors the CPU usage and message block occupancy rate of the CPUS in real time. Upon detecting a high CPU usage or message block occupancy rate, the CPUS software starts basic flow control, which is performed on non-critical functions, such as printing and logging. When the CPU usage or message block occupancy rate reaches or exceeds their respective thresholds, the CPUS software starts the following flow control functions if they are enabled:

Access control

RRC flow control

Flow control over the Iur interface

CBS flow control

Cell or URA update flow control

Flow control over the Iur-g interface

In addition, the CPUS software supports queue-based RRC shaping, which helps stabilize the CPU usage.

3.3.2 CPUS Basic Flow Control

Principle

Basic flow control for a CPUS is performed on printing, debugging, performance monitoring, logging, and resource auditing. The CPUS software monitors the CPU usage and message block occupancy rate of

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the CPUS in real time. Based on the monitored data, the CPUS software starts or stops all or some of the basic flow control functions.

When the CPU usage or message block occupancy rate reaches the threshold, the CPUS software starts flow control.

When the CPU usage and message block occupancy rate fall below their respective thresholds, the CPUS software stops flow control.

The SET FCSW command is used to enable the basic flow control functions. By default, all basic flow control functions are enabled.

The SET FCCPUTHD command is used to configure the thresholds for flow control based on CPU usage, and the SET FCMSGQTHD command is used to configure the thresholds for flow control based on message block occupancy rate.

Basic flow control for the CPUS has no impact on services.

Overload Indication

When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for an XPU, check the subrack number and slot number in the alarm.

EVT-22835 Flow Control is reported when a basic flow control function is started. To find out which basic flow control function was started, check the flow control type in the event.

The following counters indicate the CPU usage and message block occupancy rate.

Counter Description

VS.XPU.CPULOAD.MEAN Average CPU usage of the XPU

VS.XPU.MSGLOAD.MEAN Average message block occupancy rate of the XPU

3.3.3 Access Control

Principle

When the network is heavily loaded, an access class (AC) identifies the access priority of specific UEs. ACs are numbered from 0 to 15. If the CPU usage of a CPUS is higher than the preset threshold, the CPUS software restricts the access of UEs of AC0 through AC9. This reduces the impact of traffic on the network.

The RNC starts access control when the CPU usage of the CPUS exceeds the value of ACCTHD configured with the SET FCCPUTHD command or the message block occupancy rate exceeds the value of ACCTHD configured with the SET FCMSGQTHD command.

After the RNC starts access control for the CPUS, all cells under the CPUS are affected. The RNC first starts access control for a random cell. After a period of time defined by AcIntervalOfCell, the RNC starts access control for another random cell. This pattern continues until access control has been started for all cells under the CPUS.

Users of certain ACs cannot access the access-controlled cell for each period of time defined by AcRstrctIntervalLen. The number of ACs affected by access control in each period is 10 times the value of AcRstrctPercent, and the ACs are chosen in turn. Assuming that the value of AcRstrctPercent is 20%, AC0 and AC1 users cannot initiate RRC connections under the cell during the first period of time defined by AcRstrctIntervalLen, and AC2 and AC3 users cannot initiate RRC

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connections under the cell during the second such period. This pattern continues under a cell this way until access control is stopped for this cell, as shown in Figure 3-4.

Figure 3-4 Access control on users under a cell when the value of AcRstrctPercent is 20%

The RNC stops access control when the CPU usage of the CPUS falls below the value of ACRTHD configured with the SET FCCPUTHD command and the message block occupancy rate of the CPUS falls below the value of ACRTHD configured with the SET FCMSGQTHD command.

Whether access control yields noticeable effects depends on the following factors: how the operator defines users. If SIM cards are evenly distributed among ACs before being sold, access control can yield noticeable effects.

To determine whether AC is yielding notable effects, run the DSP UCELLACR command or check the value of the counter VS.RRC.AttConnEstab.Msg. Assuming AcRstrctPercent is set to 20%, access control is considered yielding noticeable effects if the value of this counter is 20% less than its value before access control was enabled.

By default, access control is disabled. To enable it, set the values of ACSW and AcRstrctSwitch to ON. Users making emergency calls are all put into AC10 and are not subject to access control.

The RNC can perform domain-specific access control (DSAC) to differentiate between the CS domain and the PS domain. When one domain is overloaded or unavailable, DSAC keeps the other domain from being negatively affected. This makes the network more resilient in the event of service interruption. For more details about DSAC, see the DSAC Feature Parameter Description.

Overload Indication


Access control uses system information to prevent users in certain ACs from accessing the network. To determine access control effects on the RNC side, compare the values of the counter VS.RRC.AttConnEstab.Msg before and after access control is enabled. This counter indicates the total number of RRC connection requests that the RNC has received from UEs.

DSAC.htm

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3.3.4 Paging Control

Principle

Upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold, the RNC starts paging control to reduce paging traffic and ensure high paging success rates for high-priority services. The PAGESW parameter in the SET FCSW command is used to enable paging control. By default, it is enabled.

When the CPU usage or message block occupancy rate exceeds the threshold, the RNC starts paging control and discards paging messages.

When the CPU usage and message block occupancy rate fall below their respective thresholds, the RNC stops paging control.

Paging control based on CPU usage varies by service. The SET FCCPUTHD command is used to configure paging control thresholds for different services, as described in Table 3-2.

Table 3-2 Thresholds for paging control based on CPU usage

Service Types Threshold for Starting Paging Control

Threshold for Stopping Paging Control

Real-time services CPAGECTHD CPAGERTHD

BE services, supplementary services, and location services

SLPAGECTHD SLPAGERTHD

SMS SMPAGECTHD SMPAGERTHD

To ensure a high paging success rate for high-priority services, such as CS services, the thresholds for starting paging control should be ranked as follows:

CPAGECTHD > SLPAGECTHD > SMPAGECTHD

This way, when paging control is in progress, SMS paging messages are the first to be discarded.

Paging control applies to terminating UEs, and load sharing is not used for paging messages. As a result, paging control for one CPUS affects all paging processes within the same RNC. The thresholds for starting paging control should be higher than the thresholds for starting other flow control functions triggered by CPUS overload.

Paging control based on message block occupancy rate does not vary by service. The necessary thresholds are configured with the SET FCMSGQTHD command.

Overload Indication


The following counters are related to paging control.

Counter Description

VS.Paging.FC.Disc.Num.CPUS

Number of paging messages discarded because of paging control

VS.Paging.FC.Disc.Time.CPU Duration of paging control in a measurement period

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Counter Description

S

3.3.5 RRC Flow Control

Principle

Upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold, the RNC starts rejecting or discarding RRC connection requests to avoid raising the CPU load further. RRC Flow Control is enabled by default. It is started after load sharing fails for RRC connection requests. For more details on load sharing for RRC connection requests, see chapter 7 "Load Sharing."

When the CPU usage or message block occupancy rate of the CPUS exceeds the threshold, the RNC starts RRC flow control and rejects RRC connection requests. When the number of rejected RRC connection requests exceeds the value of SysRrcRejNum configured with the SET UCALLSHOCKCTRL command, the CPUS starts discarding subsequent RRC connection requests messages, without responding with RRC CONNECTION REJECT messages. When the CPU usage and message block occupancy rate fall below their respective thresholds, the RNC stops RRC flow control.

RRC flow control varies by service. The SET SHARETHD command is used to configure the necessary thresholds for the different services, as shown in Table 3-3.

Table 3-3 Thresholds for RRC flow control

Service Type Threshold for Starting RRC Flow Control Based on CPU Usage

Threshold for Stopping RRC Flow Control Based on CPU Usage

Threshold for Starting RRC Flow Control Based on Message Block Occupancy Rate

Threshold for Stopping RRC Flow Control Based on Message Block Occupancy Rate

Inter-RAT cell reselection, IMSI detach procedure, registration, and incoming voice calls

CRRCCONNCCPUTHD

CRRCCONNRCPUTHD

CRRCCONNCMSGTHD

CRRCCONNRMSGTHD

BE services and UE-originated voice calls

LRRCCONNCCPUTHD

LRRCCONNRCPUTHD

LRRCCONNCMSGTHD

LRRCCONNRMSGTHD

SMS SMRRCCONNCCPUTHD

SMRRCCONNRCPUTHD

SMRRCCONNCMSGTHD

SMRRCCONNRMSGTHD

To ensure high-priority services such as CS services are processed first, the thresholds for starting RRC flow control should be ranked as follows:

CRRCCONNCCPUTHD > LRRCCONNCCPUTHD > SMRRCCONNCCPUTHD

This way, when RRC flow control is in progress, RRC connection requests for SMS are the first to be discarded.

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When the CPU usage of the CPUS exceeds 90%, the RNC starts discarding all RRC connection requests except those for emergency calls.

Overload Indication


The following counters indicate the number of RRC connection requests discarded because of RRC flow control.

Counter Description

VS.LowPriRRC.FC.Disc.Num.CPUS Number of discarded RRC connection requests for SMS because of RRC flow control based on CPU usage

VS.NormPriRRC.FC.Disc.Num.CPUS

Number of discarded RRC connection requests for BE services and outgoing voice services because of RRC flow control based on CPU usage

VS.HighPriRRC.FC.Disc.Num.CPUS Number of discarded RRC connection requests for registration and incoming voice services because of RRC flow control based on CPU usage

3.3.6 Flow Control on Signaling Messages over the Iur Interface

Principle

Upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold, the RNC starts flow control to reduce signaling traffic over the Iur interface so that the CPU load does not rise further.

When the CPU usage or message block occupancy rate exceeds the threshold, the RNC starts flow control over the Iur interface and discards signaling messages over the Iur interface.

When the CPU usage and message block occupancy rate fall below their respective thresholds, the RNC stops flow control over the Iur interface.

Flow control on signaling messages over the Iur interface consists of uplink transmission flow control over the Iur interface and downlink transmission flow control over the Iur interface, as described in Table 3-4.

Table 3-4 Flow control over the Iur interface

Flow Control Function Flow Control Objects Switch

Uplink transmission flow control over the Iur interface

UPLINK SIGNALLING TRANSFER INDICATION messages

IURULSW

Downlink transmission flow control over the Iur interface

RADIO LINK SETUP REQUEST messages

PAGING REQUEST messages

COMMON TRANSPORT CHANNEL RESOURCES REQUEST messages

IURDLSW

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Flow control over the Iur interface affects cell updates, handovers, and paging over the Iur interface. In addition, It affects ongoing service procedures because signaling messages are discarded. This may increase call drop rates.

Overload Indication


3.3.7 CBS Flow Control

Principle

In cases where the UTRAN uses an external cell broadcast center (CBC) to provide the cell broadcast service (CBS), the RNC starts CBS flow control upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold. This reduces signaling traffic over the Iu-BC interface and thereby prevents the CPU load from rising further. The CBSSW parameter in the SET FCSW command is used to enable CBS flow control. By default, it is enabled.

When the CPU usage or message block occupancy rate exceeds the threshold, the RNC starts CBS flow control and discards all CBC broadcast messages.

When the CPU usage and message block occupancy rate fall below their respective thresholds, the RNC stops CBS flow control.


CBS flow control affects cell broadcast services.

Overload Indication


The following counters are related to CBS flow control.

Counter Description

VS.CBS.FC.Disc.Num.CPUS Number of broadcast messages discarded because of CBS flow control

VS.CBS.FC.Disc.Time.CPUS Duration of CBS flow control in a measurement period

3.3.8 Cell/URA Update Flow Control

Principle

Upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold, the RNC starts cell/URA update flow control to reduce the number of cell/URA update

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messages so that the CPU load does not rise further. The CELLURASW parameter in the SET FCSW command is used to enable cell/URA update flow control. By default, it is enabled.

When the CPU usage or message block occupancy rate exceeds the threshold, the RNC starts cell/URA update flow control. During cell/URA update flow control, the RNC discards cell or URA update requests originated by a UE in the CELL_PCH or URA_PCH state that involves a P2P transition (CELL_PCH to URA_PCH or URA_PCH to CELL_PCH) or a P2F transition (CELL_PCH or URA_PCH to CELL_FACH).

When the CPU usage and message block occupancy rate fall below the threshold, the RNC stops cell/URA update flow control.


Cell/URA update flow control lowers the cell update success rate and affects uplink data transmission. In addition, UE locations recorded by the RNC may not be accurate because cell update messages are discarded. This may affect paging.

For more details about UE state transitions, see the State Transition Feature Parameter Description.

Overload Indication


The following counters are related to cell/URA update flow control.

Counter Description

VS.CU.FC.Disc.Num.CPUS Number of cell update requests discarded because of cell/URA update flow control

VS.CU.FC.Disc.Time.CPUS Duration of cell/URA update flow control in a measurement period

3.3.9 Flow Control over the Iur-g Interface

Principle

Upon detecting that the CPU usage or message block occupancy rate of a CPUS is higher than the preset threshold, the RNC starts Iur-g flow control to reduce signaling traffic over the Iur-g interface so that the CPU load does not rise further. The IURGSW parameter in the SET FCSW command is used to enable flow control over the Iur-g interface. By default, it is disabled.

When the CPU usage or message block occupancy rate exceeds the threshold, the RNC starts flow control and discards all messages sent over the Iur-g interface.

When the CPU usage and message block occupancy rate fall below their respective thresholds, the RNC stops flow control over the Iur-g interface.


When flow control over the Iur-g interface is started, the RNC is not informed of real-time information about the GSM network load. This may cause the following problems:

State%20Transition.htm

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When the GSM network load is heavy, inter-RAT handovers initiated by the RNC fail.

When the GSM network load is light, the RNC does not initiate inter-RAT handovers, service distribution cannot be performed for UMTS services, and load sharing cannot be achieved between the UMTS and GSM networks.

For more details about load-based handovers, service distribution, and load balancing over the Iur-g interface, see the Common Radio Resource Management Feature Parameter Description.

Overload Indication

When the CPU usage reaches the preset threshold, ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for an XPU, check the subrack number and slot number in the alarm.

3.3.10 Queue-based RRC Shaping

Principle

When new service attempts generate a traffic volume that exceeds the maximum processing capability of the CPU in a CPUS, the CPU usage rises to a high level. When a large number of service setup attempts are made in a short period of time, the CPU usage fluctuates sharply. To address these problems, the RNC adopts a token- and queue-based shaping solution, which performs flow control on RRC connection requests. This solution stabilizes the CPU usage and increase RRC and RAB setup success rates when traffic is heavy.

Tokens are permits to use the CPU resources of the CPUS. When an RRC connection request arrives, it applies for a token. RRC connection processing can proceed only after being granted a token. If the RRC connection request fails to obtain a token, it attempts to enter a specific queue and remains there until a token is available. If the queue is full, the RRC connection request is discarded. Figure 3-5 shows how queue-based RRC shaping works.

Figure 3-5 Queue-based RRC shaping

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By default, queue-based RRC shaping is disabled. To enable it, run the SET UCACALGOSWITCH command with the RsvdPara1 parameter set to RSVDBIT14-1.

When an RRC connection request arrives, if the CPU usage of a CPUS is higher than 90%, the CPUS discards all RRC connection requests that are not from emergency calls. If the CPU usage is not higher than 90%, the CPUS checks whether the CPU load meets the conditions for load sharing. If so, the CPUS forwards the RRC connection request to the MPU for load sharing. If not, RNC performs queue-based RRC shaping. For details about load sharing, see chapter 7 "Load Sharing." Queue-based RRC shaping is as follows:

1. The RRC connection request applies for a token.

− If the request manages to obtain a token, the request is processed and this procedure ends.

− If the request fails to obtain a token and the queue is not full, the request enters the queue. Step 2 starts.

− If the request fails to obtain a token and the queue is full, the request is discarded and this procedure ends.

2. The RRC connection request enters the queue.

3. The RRC connection request leaves the queue.

− The CPUS periodically scans the queues. If the RRC connection request has remained in a queue for longer than half of the value of T300, the CPUS discards the message.

− If a token is available for the request, the request leaves the queue and is processed. Step 4 starts.

The CPUS first processes RRC connection requests from emergency calls and terminated voice calls.

4. The CPUS processes the RRC connection request.

The RNC does not perform flow control on emergency calls, and emergency calls do not enter queues.

Overload Indication


The counter VS.RRC.FC.Disc.Num.RRCQueue.CPUS indicates the number of RRC connection requests discarded because of queue-based RRC shaping.

3.4 Flow Control Triggered by MPU Overload

3.4.1 Basic Flow Control for the MPU

Principle

Basic flow control for an MPU is performed on printing, debugging, and logging. The MPU software monitors the CPU usage and message block occupancy rate of the MPU in real time. Based on the monitored data, the MPU software starts or stops all or some of the basic flow control functions.

When the CPU usage or message block occupancy rate reaches the threshold, the MPU software starts flow control.

When the CPU usage and message block occupancy rate fall below the threshold, the MPU software stops flow control.


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The SET FCSW command is used to enable the basic flow control functions. By default, all basic flow control functions are enabled. Basic flow control for the MPU has no impact on services.

Overload Indication



The following counters indicate the CPU usage and message block occupancy rate.

Counter Description

VS.XPU.CPULOAD.MEAN Average CPU usage of the XPU

VS.XPU.MSGLOAD.MEAN Average message block occupancy rate of the XPU

3.4.2 MPU Overload Backpressure

Principle

Under heavy traffic, the CPU of the MPU may be overloaded and fail to process services properly as a result. The RNC adopts an overload backpressure function. With this function, CPUSs work with MPUs to perform flow control on RRC CONNECTION REQUEST messages to alleviate the impact of heavy traffic on MPUs.

Congestion detection is performed based on the instantaneous CPU usage of the MPU. When the CPU usage of the MPU reaches 80% (this percentage is unconfigurable) or higher, the MPU sends a congestion message to the CPUS bound to it, as shown in Figure 3-6.

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Figure 3-6 Flow control based on MPU overload

Upon receipt of the congestion message from the MPU, the CPUS adjusts the flow control level. The RNC adjusts the number of RRC connection requests that can be admitted on the CPUS each second according to the flow control level change. Flow control for the CPUS is performed on a scale of 30 levels. A higher flow control level means fewer RRC connection requests admitted each second.

The CPUS adjusts the flow control level by using two timers, one with a value of 2.2 seconds, the other with a value of 0.8 seconds.

Upon receiving a congestion message from the MPU, the CPUS increases the flow control level by one and starts the two timers.

If MPU congestion messages are received before the 0.8-second timer expires, the CPUS does not take any actions.

If MPU congestion messages are received after the 0.8-second timer expires but before the 2.2-second timer expires, the CPUS increases the flow control level by one and restarts the two timers. After the 2.2-second timer expires, the CPUS decreases the flow control level by one.

When the RsvdPara1 parameter in the SET URRCTRLSWITCH command is set to RSVDBIT1_BIT19-1, MPU overload backpressure is enabled. By default, it is enabled.

Overload Indication


The counter VS.RRC.FC.Disc.Num.MPU.CPUS indicates the number of RRC connection requests discarded because of MPU overload backpressure.

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3.5 Flow Control Triggered by INT Overload

3.5.1 INT Basic Flow Control

Principle

When an interface board (INT) is heavily loaded, it starts basic flow control. Basic flow control for an INT is performed on printing, debugging, and logging. The INT software monitors the CPU usage and message block occupancy rate of the INT in real time. Based on the monitored data, the INT software starts or stops all or some of the basic flow control functions.

When the CPU usage or message block occupancy rate reaches the threshold, the INT software starts flow control.

When the CPU usage and message block occupancy rate fall below the threshold, the INT software stops flow control.

The SET FCCPUTHD command is used to configure the thresholds for flow control based on CPU usage, and the SET FCMSGQTHD command is used to configure the thresholds for flow control based on message block occupancy rate. Basic flow control for the INT has no impact on services.


Overload Indication

When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for an INT, check the subrack number and slot number in the alarm.


The counter VS.INT.CPULOAD.MEAN indicates the CPU usage.

3.5.2 Flow Control Triggered by INT Overload on the Control Plane

Principle

After a UE initiates an RRC connection request and obtains transmission resources on the MPU, the CPUS sends a session setup request to the interface board. When a large number of service setup requests are made in a short period of time, the interface board needs to process a large number of session setup requests and may be overloaded. The MPU adopts a flow control process based on service priorities and the instantaneous CPU usage of the interface board. This type of flow control improves the RAB setup success rate when the interface board is heavily loaded.

The interface board reports its CPU usage to the MPU each second, as shown in Figure 3-7. Based on the CPU usage of the interface board, the MPU adjusts the maximum number of session setup requests admitted by the interface board. If the number of RRC connection requests already admitted is larger than the maximum number allowed, the RNC only processes RRC connection requests from emergency calls and high-priority services. The switch parameter for this function is SwitchParameter1 in the SET SS7PATCHSWITCH command. When SwitchParameter1 is set to OFF, this function is enabled. It is enabled by default and applies to Iub, Iu, and Iur interface boards. The maximum number of session setup requests allowed determines the signaling processing capability of the interface board. High-priority services involved in this type of flow control refer to incoming and outgoing voice calls, inter-RAT cell reselection, and registration.

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Figure 3-7 Flow control triggered by INT overload

When the CPU usage of the interface board exceeds 90%, the MPU starts discarding RRC connection requests from all UEs.

Overload Indication

When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for an INT, check the subrack number and slot number in the alarm.

3.5.3 Flow Control Triggered by Iub Interface Board Overload on the User Plane

When the amount of user-plane data sent from the DPU to the interface board exceeds the processing capability of the interface board, the interface board throughput decreases and the packet loss rate increases. To address this problem, the RNC adopts backpressure-based downlink congestion control. For more details, see the Transmission Resource Management Feature Parameter Description.

3.6 Flow Control Triggered by DPU Overload

3.6.1 DPU Basic Flow Control

Principle

When a DPU is heavily loaded, it starts basic flow control. Basic flow control for a DPU is performed on printing, debugging, and logging. The DPU software monitors the CPU usage and message block occupancy rate of the DPU in real time. Based on the monitored data, the DPU software starts or stops all or some of the basic flow control functions.

Transmission%20Resource%20Management.htm

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When the CPU usage or message block occupancy rate reaches the threshold, the DPU software starts flow control.

When the CPU usage and message block occupancy rate fall below the threshold, the DPU software stops flow control.

The SET FCCPUTHD command is used to configure the thresholds for flow control based on CPU usage, and the SET FCMSGQTHD command is used to configure the thresholds for flow control based on message block occupancy rate. Basic flow control for the DPU has no impact on services.


Overload Indication

When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for a DPU, check the subrack number and slot number in the alarm.


3.6.2 Flow Control Triggered by DSP CPU Overload

Principle

To ensure admission of CS services and quality of ongoing CS services, the RNC lowers the rates of BE services when the CPU of a DSP is heavily loaded. By default, this type of flow control is enabled.

Each DSP of the DPU periodically monitors its own CPU usage.

When the CPU usage is between SSDSPAVEUSAGEALMTHD and SSDSPMAXUSAGEALMTHD, the RNC lowers the rates of BE services.

When the CPU usage is lower than the threshold SSDSPAVEUSAGEALMTHD, the RNC raises the rates of BE services.

To prevent the DSP from crashing, if the CPU usage is higher than 90% during a monitoring period, the RNC further lowers BE service rates and discards some packets of BE services and AMR services.

When the RNC raises or lowers service rates, the current monitoring period is ended. To prevent frequent changes in service rates, the RNC waits a period of time before starting the next monitoring period. During this period, the RNC does not increase or decrease rates of BE services.

Overload Indication

There are no indications when the CPU of a DSP is overloaded.

3.7 Flow Control Triggered by SCU Overload

3.7.1 Principle

When an SCU is heavily loaded, it starts basic flow control. Basic flow control for an SCU is performed on printing, debugging, performance monitoring, and logging. The SCU software monitors the CPU usage and message block occupancy rate of the SCU in real time. Based on the monitored data, the SCU software starts or stops all or some of the basic flow control functions.

When the CPU usage or message block occupancy rate reaches the threshold, the SCU software starts flow control.

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When the CPU usage and message block occupancy rate fall below the threshold, the SCU software stops flow control.

The SET FCCPUTHD command is used to configure the thresholds for flow control based on CPU usage, and the SET FCMSGQTHD command is used to configure the thresholds for flow control based on message block occupancy rate. Basic flow control for the SCU has no impact on services.


3.7.2 Overload Indication

When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for an SCU, check the subrack number and slot number in the alarm.


The counter VS.SCU.CPULOAD.MEAN indicates the CPU usage.

3.8 Flow Control Triggered by GCU Overload

3.8.1 Principle

When a GCU is heavily loaded, it starts basic flow control. Basic flow control for a GCU is performed on printing, debugging, and logging. The GCU software monitors the CPU usage and message block occupancy rate of the GCU in real time. Based on the monitored data, the GCU software starts or stops all or some of the basic flow control functions.

When the CPU usage or message block occupancy rate reaches the threshold, the GCU software starts flow control.

When the CPU usage and message block occupancy rate fall below the threshold, the GCU software stops flow control.

The SET FCCPUTHD command is used to configure the thresholds for flow control based on CPU usage, and the SET FCMSGQTHD command is used to configure the thresholds for flow control based on message block occupancy rate. Basic flow control for the GCU has no impact on services.



When the CPU usage reaches the preset threshold (configured by the SET CPUTHD command), ALM-20256 CPU Overload is reported. To find out whether the alarm was reported for a GCU, check the subrack number and slot number in the alarm.


The counter VS. GCU.CPULOAD.MEAN indicates the CPU usage.

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Flow Control 4 Flow Control Triggered by NodeB/Cell Overload



4-1

4 Flow Control Triggered by NodeB/Cell Overload

4.1 CAPS Control

4.1.1 Principle

When the number of calls in a cell or NodeB sharply increases, most system resources (mainly radio resources) are consumed processing the enormous amount of RRC connection setup requests. Therefore, the remaining resources are insufficient for processing subsequent RAB assignment requests, resulting in call failures.

To solve this problem, the RNC implements the CAPS control function. This function limits the number of RRC connection requests admitted to a cell or NodeB each second. By preventing the traffic of a single cell or NodeB from surging, CAPS control helps maintain a stable traffic volume on the network. Figure 4-1 shows the procedure for CAPS control.

Figure 4-1 Procedure for CAPS control

By default, CAPS control is disabled.

To enable cell-level CAPS control:

− Set the CallShockCtrlSwitch parameter to SYS_LEVEL-0&NODEB_LEVEL-0&CELL_LEVEL-1; and

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− Set the RsvdPara1 parameter (by running the ADD UCELLALGOSWITCH command) to RSVDBIT4-1.

To enable NodeB-level CAPS control:


− Set the RsvdPara1 parameter (by running the ADD UNODEBALGOPARA command) to RSVDBIT1-1.

To enable both cell-level and NodeB-level CAPS control:


− Set the RsvdPara1 parameter (by running the ADD UCELLALGOSWITCH command) to RSVDBIT4-1. Set the RsvdPara1 parameter (by running the ADD UNODEBALGOPARA command) to RSVDBIT1-1.

The CallShockCtrlSwitch parameter is for the RNC. To enable cell- or NodeB-level CAPS control, you need to set the associated parameter for the cell or NodeB. The SYS_LEVEL field of the CallShockCtrlSwitch parameter is used to enable CPUS-level CAPS control, which is no longer applicable.

After CAPS control is enabled, the RNC periodically checks the total number of RRC connection requests received by a cell or NodeB. When this number exceeds the preset threshold, the RNC triggers the cell- or NodeB-level flow control. The check period is set with the CallShockJudgePeriod parameter. Table 4-1 describes the conditions for triggering the cell- and NodeB-level flow control.

Table 4-1 Conditions for triggering the cell- and NodeB-level flow control

Flow Control Level Triggering Condition

Cell The total number of RRC connection requests received by a cell during a specified period exceeds the value of CellTotalRrcNumThd.

NodeB The total number of RRC connection requests received by a NodeB during a specified period exceeds the value of NBTotalRrcNumThd; or

NCP link congestion over the Iub interface is detected.

Table 4-2 describes the flow control policy for different services.

Table 4-2 Flow control policy

Service Flow Control Policy

PS BE services (interactive service and background service), streaming service, short message service (SMS), and inter-RAT cell change

The RNC rejects the access requests of these services.

AMR service Cell-level flow control:

The number of RRC connection requests admitted for AMR services in a cell each second must not exceed the value of the CellAmrRrcNum parameter. Once the limit is reached, the RNC rejects all subsequent requests.

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Service Flow Control Policy

NodeB-level flow control:

The number of RRC connection requests admitted for AMR services in a NodeB each second must not exceed the value of the NBAmrRrcNum parameter. Once the limit is reached, the RNC rejects all subsequent requests.

Registration and inter-RAT cell reselection

When the RegByFachSwitch parameter is set to ON, the RNC forcibly sets up the RRC connection of registrations on the FACH.

Cell-level flow control:

The number of RRC connection requests for registrations and inter-RAT cell reselections in a cell each second must not exceed the value of the CellHighPriRrcNum parameter. Once the limit is reached, the RNC rejects all subsequent requests.

NodeB-level flow control:

The number of RRC connection requests for registrations and inter-RAT cell reselections in a NodeB each second must not exceed the value of the NBHighPriRrcNum parameter. Once the limit is reached, the RNC rejects all subsequent requests.

Emergency call Flow control is not applied to emergency calls.

To prevent a UE from frequently retransmitting the RRC connection requests, the RNC adds an IE "wait time" to the RRC connection reject message sent to the UE. The UE waits for the length of time specified by RrcConnRejWaitTmr and then retransmits the RRC connection request. In this way, network congestion will not be aggravated. The UE needs to support the processing associated with "wait time."


The counter VS.RRC.FC.Disc.Num.CallShock.CPUS indicates the number of RRC connection requests discarded on the CPUS because of CAPS control.

4.2 PCH Congestion Control

4.2.1 Principle

Because PS services are growing so rapidly, the number of paging messages consuming a large amount of paging resources is also increasing rapidly. As a result, the paging success rate of CS services may be affected. To address this issue, the RNC implements PCH congestion control. With PCH congestion control, CS services are allowed to preempt the paging resources of PS services in the event of PCH congestion, increasing the paging success rate of CS services.

When the number of transmitted paging messages in a transmission time interval (TTI) reaches the maximum (known as PCH congestion), push to talk (PTT) services and conversational services can start preempting the paging resources of other services. If preemption fails, the paging message for a PTT or conversational service is discarded. The rules for PCH congestion control are as follows:

PTT services can preempt the paging resources of other services but its resources cannot be preempted by other services.

Conversational services can preempt the paging resources of non-conversational services.

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The paging messages of other services (except PTT services and conversational services) are discarded.

By default, PCH congestion control is disabled. To enable PCH congestion control and allow the conversational services to preempt the paging resources of non-conversational services, run the SET UDPUCFGDATA command to set PAGINGSWITCH to ON.

If the value of the counter VS.RRC.Paging1.Loss.PCHCong.Cell is not 0, the PCH is congested. If this happens, enable PCH congestion control and do not disable it once it is enabled.


When the PCH is congested, the paging messages are discarded. The counter VS.RRC.Paging1.Loss.PCHCong.Cell indicates the number of discarded paging messages.

When the PCH congestion control function is enabled, CS services can preempt the paging resources of PS services. The counter VS.RRC.Paging1.PCHCong.CSPreemptAtt indicates the number of paging preemptions by CS services in a cell due to PCH congestion.

4.3 FACH Congestion Control

4.3.1 Overview

The Forward Access Channel (FACH) is a downlink common transport channel that carries control messages to a UE during initial access and state transition. The FACH may also carry a small quantity of user-plane data. FACH congestion may block information exchange between UEs and the network, affecting service provisioning. To address this issue, the RNC implements FACH congestion control. FACH congestion may be due to the fact that the number of UEs in the CELL_FACH state is limited, or the fact that the resources of the logical channels (CCCH/DCCH) on the FACH are congested. Table 4-3 describes how flow control is implemented in different scenarios where FACH congestion is the problem.

Table 4-3 FACH flow control

Cause of FACH Congestion

Flow Control Actions

Limited number of UEs in the CELL_FACH state

The P2D transitions is triggered.

The D2Idle transitions of PS BE services is triggered.

CCCH congestion Message retransmission for PS BE services is stopped.

New PS BE services are rejected.

DCCH congestion The P2D transitions of CS services is triggered.

When there is CCCH/DCCH congestion on the FACH, the RNC performs flow control based on the congestion level. The congestion level is determined by comparing the channel buffer size and the preset thresholds, as described in Table 4-4.

Table 4-4 Determination on CCCH/DCCH congestion level

Congestion Level

Determining Condition Parameter for CCCH Parameter for DCCH

Non-congestion Channel buffer size less than the congestion clearance threshold

RsvdPara14 None

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Congestion Level

Determining Condition Parameter for CCCH Parameter for DCCH

Minor congestion Channel buffer size greater than or equal to the congestion threshold

RsvdPara3 None

Major congestion Channel buffer size greater than or equal to the discard threshold

None None

The congestion and congestion clearance thresholds for CCCH are set by using the SET UDPUCFGDATA command. Keep the default values (60 for the congestion threshold and 30 for the congestion clearance threshold). If you need to modify the parameter settings, consult Huawei technical support because the modification affects flow control. The congestion and congestion clearance thresholds for DCCH are not configurable. The default value for the congestion threshold is 60, and the default value for the congestion clearance threshold is 10.

For details about WCDMA channels, see the Radio Bearers Feature Parameter Description. For details about state transitions, see the State Transition Feature Parameter Description.

4.3.2 Flow Control Based on Limited Number of UEs in the CELL_FACH State

Principle

Generally, a state transition from CELL_DCH to CELL_FACH (referred to as a D2F transition) shall occur

if Event 4B is triggered, as indicated by procedure in Figure 4-2. Event 4B is triggered when the traffic volume of the UE is low for some time. If a UE in the CELL_PCH or URA_PCH state needs to transmit data or respond to a paging message, it initiates a cell update message to enter the CELL_FACH state, as shown in procedure in Figure 4-2.

The number of UEs on the FACH (UEs in the CELL_FACH state) is limited in a cell. The two types of state transition previously mentioned may fail if the number of UEs in the CELL_FACH state reaches the limit. As a result, UEs in the CELL_DCH state, having little or no data to transmit, may continuously occupy the dedicated channels and cell resource utilization may decrease as a result. UEs in the CELL_PCH or URA_PCH state may also fail to perform data transmission or respond to paging messages and finally enter the idle state, leading to PS service drops. The maximum number of UEs in the CELL_FACH state is 30.

Radio%20Bearers.htm


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Figure 4-2 UE state transitions

The RNC allows D2Idle transitions (procedure in Figure 4-2) and P2D transitions (procedure in Figure 4-2), when the number of UEs in the CELL_FACH state has reached the upper limit. Table 4-5 describes the triggering conditions for these state transitions.

Table 4-5 Triggering conditions for a D2Idle transition and a P2D transition

UE State State Transition

Triggering Condition Switch

CELL_DCH D2Idle Event 4B triggers a D2F state transition.

The D2F state transition fails two consecutive times because of the limit to the number of UEs in the CELL_FACH state.

The ReservedSwitch0 parameter is set to RESERVED_SWITCH_0_BIT16-1.

CELL_PCH/URA_PCH

P2D The cause of a cell update is "uplink data transmission" or "paging response", triggering a P2F transition.

The P2F transition fails because the number of UEs in the CELL_FACH state has reached the upper limit.

The RsvdPara1 parameter is set to RSVDBIT1_BIT20-1.

The D2Idle transition function is disabled by default, and can be enabled by running the SET UCORRMALGOSWITCH command. After a UE moves to the idle state, the RNC releases the dedicated channel for the UE in order to improve the cell resource utilization.

The P2D transition function is disabled by default, and can be enabled by running the SET URRCTRLSWITCH command. During a P2D transition, the RNC delivers the UE a cell update confirm message on the CCCH, which prevents call drops because the delivery does not use up resources designated for UEs in the CELL_FACH state. The initial access rate of a PS service is 8 kbit/s after the UE has entered the CELL_DCH state.

The rate of PS BE services (non-PTT services) can be limited to 8 kbit/s to prevent excess usage of the DCH resources. This function can be enabled by running the SET UCORRMALGOSWITCH

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command with the ReservedSwitch1 parameter set to RESERVED_SWITCH_1_BIT6-1. This function is enabled by default.

If the number of UEs in the CELL_FACH state reaches the upper limit, cell updates may fail, including those triggered by radio link setup failures. As a result, call drops may occur. To prevent this, you can reserve some UEs in the CELL_FACH state for cell updates. To set the number of reserved users, run the SET UCORRMALGOSWITCH command and modify the ReservedU32Para1 parameter.

If the number of reserved UEs in the CELL_FACH state is 5, the D2F transition shown in Figure 4-2 will not be implemented when the number of UEs in the CELL_FACH state reaches 25. Instead, the D2Idle transition may be triggered. The resources for reserved UEs are for the users who send cell update messages.

If the value of the counter VS.CellFACHUEs (the number of UEs in the CELL_FACH state) is greater than or equal to 25, enable the P2D transition and the D2Idle transition.

For details about UE state transition in normal cases, see the State Transition Feature Parameter Description.

Overload Indication

The counter VS.CellFACHUEs indicates the number of UEs in the CELL_FACH state.

4.3.3 CCCH Flow Control

Principle

The common control channel (CCCH) is a logical channel that transmits control messages, such as RRC messages and cell update confirm messages, between the RNC and UEs. The CCCH processes the received messages in its buffer in sequence. The CCCH processes the following messages:

RRC CONNECTION SETUP

RRC CONNECTION REJECT

RRC CONNECTION RELEASE

CELL/URA UPDATE CONFIRM (used during a P2D transition for cell update)

The CCCH may be congested in either of the following situations:

UEs with PS services frequently send RRC connection requests.

A large number of UE registrations (including 2G/3G cell reselections) occur within a short period.

CCCH congestion may become severer in either of the following situations:

The RNC repeatedly sends a UE the RRC connection setup message within the time specified by T381, aiming to increase the success rate of the UE receiving the RRC connection setup message.

A UE repeatedly sends the RRC connection request to the RNC if the UE does not receive the RRC connection setup message within T300. This is because the RRC connection setup message sent by the RNC the first time may have been discarded if the CCCH is congested.

To guarantee the success rate of RRC connection setup in case of CCCH congestion, the RNC implements CCCH flow control.

The RNC performs CCCH flow control differentiating the RRC connection requests according to the CCCH congestion level. The CCCH congestion level is determined by comparing the CCCH buffer size and the preset thresholds, as described in Table 4-4. Figure 4-3 shows CCCH flow control.



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Figure 4-3 CCCH flow control

In the event of minor CCCH congestion, the RNC performs flow control as follows:

For PS BE service requests, the RNC discards the retransmitted RRC connection requests after T300 expires. This means that the RNC only handles the RRC connection request transmitted for the first time. In addition, the RNC stops T381.

In the event of major CCCH congestion, the RNC performs flow control as follows:

The RNC discards RRC connection requests for new PS BE services.

CCCH flow control stops once the CCCH is no longer congested.

CCCH flow control is disabled by default. To enable it, run the MOD UCELLALGOSWITCH command and set the RsvdPara1 parameter to RSVDBIT5-1. Enable CCCH flow control in mass gathering events, in which case the traffic volume surges. Keep CCCH flow control enabled to increase the success rate of RRC connection setup when the CCCH is congested.

If CCCH congestion and Uu-interface resource (code/power/CE) congestion are detected, the RNC adds an IE "wait time" to the RRC connection reject message sent to the UE. The UE waits for the length of time specified by this IE and then retransmits an RRC connection request. When the FACH is congested, the RNC automatically sets the RrcConnRejWaitTmr parameter to 15.

Overload Indication

None

4.3.4 DCCH Flow Control

Principle

The dedicated control channel (DCCH) is a logical channel that transmits dedicated control messages, such as reconfiguration messages and cell update confirm messages, between a UE and the RNC. The DCCH processes the received messages in its buffer in sequence. The DCCH processes the following messages:

RADIO BEARER RECONFIGURATION (F2D/F2P transitions)

CELL/URA UPDATE CONFIRM (P2F cell updates)

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DOWNLINK DIRECT TRANSFER/SECURITY MODE COMMAND

The DCCH may be congested if:

UEs in the CELL_PCH state frequently initiate the PS service access requests, triggering the frequent transitions from P2F to F2D to D2F to F2P.

UEs in the CELL_PCH state frequently receive the paging messages from the CN, triggering the frequent transitions from P2F to F2D to D2F to F2P.

When a UE in unacknowledged mode (UM) initiates a F2D/F2P/P2F transition, the RNC periodically retransmits the radio bearer reconfiguration messages on the DCCH, resulting in severer DCCH congestion.

When there is minor or major congestion on the DCCH, the RNC enables P2D transitions for CS service to guarantee the CS service access. The function of P2D transition for CS service access is disabled by default. To enable it, run the SET URRCTRLSWITCH command with the RsvdPara1 parameter set to RSVDBIT1_BIT20-1.

DCCH flow control stops once the DCCH is no longer congested. The DCCH congestion level is determined by comparing the DCCH buffer size and the preset thresholds, as described in Table 4-4.

If the value of the counter VS.FACH.DCCH.CONG.TIME is not 0, the DCCH is congested. If this happens, enable DCCH congestion control and do not disable it once it is enabled.

Figure 4-4 shows the UE state transition when DCCH flow control is enabled.

Figure 4-4 UE state transition when DCCH flow control is enabled

For details about UE state transition in normal cases, see the State Transition Feature Parameter Description.

Overload Indication

The counter VS.FACH.DCCH.CONG.TIME indicates the duration of DCCH congestion.



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Flow Control 5 Flow Control over the Iu Interface



5-1

5 Flow Control over the Iu Interface

5.1 SCCP Flow Control

5.1.1 Overview

In cases where the bandwidth configured for signaling links over the Iu interface is insufficient or some signaling links over the Iu interface are faulty, signaling link congestion will occur when there are a large number of calls, location updates, or group short messages. Signaling link congestion must be quickly alleviated. Otherwise, it will lead to extended delays or even timeouts in signaling exchanges between UEs and the core network. Severe congestion may cause services to break down. To address these problems, the RNC supports Signaling Connection Control Part (SCCP) flow control, which prevents severe congestion on the signaling link between the RNC and the core network. By default, SCCP flow control is enabled.

The RNC uses a scale of 13 levels (0 to 12) to perform SCCP flow control based on service type. When the flow control level changes, the RNC adjusts the signaling traffic over the Iu interface. The higher the flow control level, the more initial UE messages will be discarded. At Level 0, flow control is not performed. The RNC performs SCCP flow control on short message services, paging, location updates and registrations. Of these, short message service has the lowest priority, and location updates and registrations have the highest priority. At a particular flow control level, the RNC proportionally discards the initial UE messages of these services. The proportion is based on service priorities and is not configurable. Of all the messages discarded during flow control, initial UE messages for lower-priority services account for the largest proportions. Assuming that 30 initial UE messages are to be discarded and the proportion of SMS messages discarded to paging messages discarded to location updates discarded is 3:2:1, the numbers of initial UE messages for different services to be discarded are calculated as follows:

SMS: 30 x 3/(3 + 2 + 1) = 15

Paging: 30 x 2/(3 + 2 + 1) = 10

Location registrations: 30 x 1/(3 + 2 + 1) = 5

SCCP flow control includes:

Flow control based on Iu signaling load

Flow control based on the SCCP setup success rate

CN SCCP congestion control

These three flow control functions have their own flow control levels, and the RNC performs SCCP flow control according to the highest among them. Table 5-1 provides details about SCCP flow control.

Table 5-1 SCCP flow control

Flow Control Method Switch Criteria for Adjusting Flow Control Levels

Flow control based on Iu signaling load

IUFCSW The SCCP receives an unsolicited SCCP-SSC message from the core network.

The SCTP link (in the case of IP transmission) or the SAAL/MTP3 link (in the case of ATM transmission) becomes congested.

Flow control based on the SCCP setup success rate

None The ratio of the sum of CC and CREF to CR changes.

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5-2

Flow Control Method Switch Criteria for Adjusting Flow Control Levels

CN SCCP congestion control

None The RNC receives a CN CREF congestion indication after sending a CR.

5.1.2 Flow Control Based on Iu Signaling Load

Principle

When the CN SCCP is congested, the RNC receives an SCCP Subsystem-Congested (SCCP-SSC) message from the CN. This message carries the CN SCCP congestion level. The RNC maps the CN SCCP congestion level to an RNC SCCP flow control level.

In addition, the RNC monitors the load on the SCTP, SAAL, or MTP3 link in real time and adjusts the flow control level based on the congestion status.

Overload Indication

When a signaling link over the Iu interface is congested, the following alarms and counters are reported:

Transmission Mode over the Iu Interface

Alarms Counters

IP transmission ALM-21542 SCTP Link Congestion VS.SCTP.CONGESTION.INTERVAL

OS.M3UA.Lnk.Cong.Dur

ATM transmission ALM-21501 MTP3 Signaling Link Congestion

ALM-21502 MTP3 DSP Congestion

ALM-21532 SAAL Link Congestion

OS.MTP3.Lnk.Cong.Dur

OS.MTP3.Lnk.ConG

VS.SAAL.LnkErr.BufferLoss

The following counters indicate the number of initial UE messages discarded because of flow control over the Iu interface.

Counter Description

VS.IU.FlowCtrl.DiscInitDT.CS

Number of initial UE messages in the CS domain that are discarded because of flow control over the Iu interface

VS.IU.FlowCtrl.Disc.InitDT.PS

Number of initial UE messages in the PS domain that are discarded because of flow control over the Iu interface

5.1.3 Flow Control Based on SCCP Setup Success Rate

Principle

In each flow control period, the RNC SCCP checks the number of connection requests (CRs) sent to the CN and the total number of Connection Confirm (CC) and Connection Refused (CREF) messages received from the CN. Each period is 5 seconds long.

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Based on the changes in the ratio of the number of CCs plus the number of CREFs to the number of CRs, the RNC SCCP adjusts the flow control level to ensure that the number of messages received by the CN does not exceed its capabilities.

The flow control level is adjusted based on the following criteria:

When (CC+CREF)/CR shows an increasing trend in a flow control period:

− Flow control is lowered by one level if it is weaker than the previous period.

− Flow control is raised by one level if it is stronger than the previous period.

If (CC+CREF)/CR shows a decreasing trend in a flow control period:

− Flow control is raised by one level if it is weaker than the previous period.

− Flow control is lowered by one level if it is stronger than the previous period.

If the number of CRs sent to the CN from the RNC increases, flow control weakens. If the number of CRs sent from the RNC decreases, flow control strengthens.

Overload Indication

There are no indications when the CN is overloaded by CRs sent from the RNC.

5.1.4 CN SCCP Congestion Control

Principle

When the CN SCCP is congested, the RNC receives a CREF message carrying a congestion indication after sending a CR. The RNC SCCP periodically checks whether it has received CREF messages carrying congestion indications. When it does, it raises the flow control level by one. Otherwise, the RNC lowers the flow control level by one.

Overload Indication

The following counters indicate the number of initial UE messages discarded because of CN SCCP congestion control.

Counter Description

VS.IU.FlowCtrl.DiscInitDT.CS Number of initial UE messages in the CS domain that are discarded because of flow control over the Iu interface

VS.IU.FlowCtrl.Disc.InitDT.PS Number of initial UE messages in the PS domain that are discarded because of flow control over the Iu interface

5.2 Flow Control Triggered by CN RANAP Overload

Principle

When the CN RANAP is overloaded (CPU overload, for example), it sends a RANAP OVERLOAD message to the RNC. Upon receipt of this message, the RNC adjusts the traffic level to the CN over the Iu interface in order to decrease the load on the CN. The IUCTHD parameter in the SET FCSW command is used to configure the percentage of the total traffic the RNC is restricted from sending to the CN. The default value of this parameter is 70, which means the RNC can only send 30% of the total traffic to the CN.

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Flow control triggered by CN RANAP overload is performed on a scale of 21 levels (0 to 20). The lower the level, the more initial UE messages are discarded. The RNC uses two timers when adjusting the flow control level: IntrTmr and IgorTmr, as shown in Figure 5-1.

Figure 5-1 Adjusting the flow control level

1. When IgorTmr was not started and the RNC receives an overload message from the CN, the RNC lowers the flow control level by one and starts IntrTmr and IgorTmr, as shown in Figure 5-1.

The CN tells the RNC how many levels to lower the flow control according to the information element Number of Steps in the RANAP OVERLOAD message.

2. If the RNC receives more overload messages from the CN before IgorTmr expires, the RNC does not adjust the flow control level again.

3. If the RNC receives an overload message from the CN when IgorTmr has expired but IntrTmr has not, the RNC lowers the flow control level by one unless the flow control level is already 0.

4. If the RNC has not received an overload message from the CN by the time IntrTmr expires, the RNC raises the flow control level by one. If the flow control level is below 20, the RNC restarts IntrTmr. The RNC repeats these operations until the flow control level reaches level 20. If the RNC receives an overload message from the CN while IntrTmr is running, the procedure returns to step 1.

By default, this type of flow control is enabled.

Overload Indication

When the CN is overloaded, ALM-22301 UMTS CN Overload is reported.

The following counters indicate the number of initial UE messages discarded because of flow control over the Iu interface.

Counter Description

VS.IU.FlowCtrl.DiscInitDT.CS Number of initial UE messages in the CS domain that are discarded because of flow control over the Iu interface

VS.IU.FlowCtrl.Disc.InitDT.PS Number of initial UE messages in the PS domain that are discarded because of flow control over the Iu interface

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Flow Control 6 Service Flow Control



6-1

6 Service Flow Control The RNC and NodeB adopt congestion control algorithms on the user plane over the Iub interface to perform flow control on BE services. This restricts user transmission rates, prevents congestion and packet loss, and optimizes bandwidth utilization over the Iub interface. For more details, see the Transmission Resource Management Feature Parameter Description.


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Flow Control 7 Load Sharing



7-1

7 Load Sharing

7.1 Overview

Load sharing is performed on both the control plane and the user plane. CPUSs, DSPs, and other boards can be bound to an MPU to form a logical subrack. The subracks mentioned in this chapter are all logical subracks.

Each CPUS controls some NodeBs and their cells. The CPUS performs signaling processing for service requests from the UEs under these cells, and the UEs are admitted to the CPUS.

The MPU in each subrack keeps a record of the user-plane load on the current subrack and shares this information with the MPUs in other subracks. When a service request arrives and the controlling CPUS is heavily loaded, the CPUS forwards the request to the MPU in the current subrack. The MPU selects the CPUS with the lightest load for signaling processing. The selected CPUS may be in the current subrack or another subrack. Figure 7-1 shows how load sharing works between two subracks.

Figure 7-1 Load sharing between two subracks

When a UE attempts to access the network and user-plane resources need to be allocated to the UE, the controlling CPUS sends a resource request to the MPU in the current subrack. The MPU attempts to allocate the user-plane resources of the current subrack to the UE. If this attempt fails, the MPU forwards the resource request to the MPU in the subrack with the lightest load.

Figure 7-2 shows resource management on the user plane.

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Figure 7-2 Resource management on the user plane

If the CPU usage of a CPUS is 90% or higher, the CPUS discards all service requests except those for emergency calls. Load sharing does not work for the CPUS.

When the CPU usage of an MPU is 95% or higher, the MPU discards the following requests to avoid resetting:

Resource requests from each UE, for example, requests for DSP resources and transmission resources

Load sharing requests

When this occurs, load sharing does not work.

7.2 Load Sharing on the Control Plane

7.2.1 Procedure for Load Sharing on the Control Plane

When a CPUS receives a service request, the controlling CPUS determines whether to perform load sharing. If so, the CPUS follows the procedure described in Figure 7-3.

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Figure 7-3 Load sharing on the control plane

Details are as follows:

Step 1 The CPUS receives a service request.

Step 2 Based on the current load, the CPUS determines whether to perform load sharing. For more details, see section 7.2.2 "Service Request Processing by a CPUS."

− If load sharing is to be performed, Step 3 starts.

− If load sharing is not to be performed, the CPUS processes the request, and the procedure ends.

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Step 3 The CPUS forwards the request to the MPU in the current subrack.

Step 4 Upon receipt of the load sharing request from the CPUS, the MPU checks the control-plane load on all subracks in the RNC.

If the control-plane load on the current subrack minus CtrlPlnSharingOutOffset is higher than the control-plane load on any other subrack, load sharing is performed between subracks.

The MPU forwards the request to the MPU in the subrack with the lightest load on the control plane, which is known as the target MPU. Following the criteria described in Table 7-1, the target MPU searches for all CPUSs that can take up the request.

− If the target MPU can find such CPUSs, it selects a CPUS with the lightest CPU load to process the request.

− If the target MPU cannot find such a CPUS, load sharing is performed within the current subrack.

If the control-plane load on the current subrack minus CtrlPlnSharingOutOffset is lower than or equal to the control-plane load on any other subrack, load sharing is performed within the current subrack. Following the criteria described in Table 7-1, the MPU in the current subrack attempts to find CPUSs that can take up the request from within the current subrack.

− If the target MPU can find such CPUSs, it selects a CPUS with the lightest CPU load to process the request.

− If the MPU cannot find such a CPUS, service access is rejected.

The control-plane load on a subrack is the average CPU usage of the CPUSs managed by the MPU.

Load sharing is yielding noticeable effects if the load is balanced across the CPUs of the CPUSs. To check the CPU load of the CPUSs, run the DSP CPUUSAGE command. If the load is not balanced, consult Huawei engineers to adjust the thresholds for load sharing or adjust the configuration of XPUs in the subracks.

7.2.2 Service Request Processing by a CPUS

Generally, CPUSs are not heavily loaded. When a user initiates a service request, the controlling CPUS processes it. If the controlling CPUS is heavily loaded, load sharing is performed and the request is forwarded to a lightly loaded CPUS. Service requests cannot be forwarded to an overloaded CPUS. The CPUS load is indicated by the CPU load (CPU usage) and CAPS. The RNC considers a CPUS overloaded when any of the following conditions is met:

The CPU load is low and the CAPS is high.

The CPU load is high and the CAPS is low.

The CPU load is greater than or equal to the CPU overload threshold, which cannot be configured.

Based on the CPUS load, the RNC defines three CPUS states, as shown in Figure 7-4.

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Figure 7-4 CPUS load and states

The state of a CPUS determines how it processes service requests, as described in Table 7-1.

Table 7-1 Service request processing by CPUS state

CPUS State Definition Processing

State I The CPUS is lightly loaded. The CPUS load is considered light when both the following are true:

CPU load ≤ CtrlPlnSharingOutThd

CAPS ≤ MaxCAPSLowLoad

The CPUS directly processes new and forwarded requests.

State II The CPUS is heavily loaded. The CPUS load is considered heavy when both the following are true:

CtrlPlnSharingOutThd < CPU load < CPU overload threshold

CAPS ≤ MaxCAPSMidLoad

The CPUS forwards all new requests to the MPU for load sharing.

The MPUs can forward requests to the CPUS.

State III The CPUS is overloaded. The CPUS is considered overloaded when any of the following is true:

CPU overload threshold < CPU load

CPU load <= CtrlPlnSharingOutThd, and MaxCAPSLowLoad < CAPS

CtrlPlnSharingOutThd < CPU load < CPU overload threshold, and MaxCAPSMidLoad < CAPS

The CPUS forwards all new requests to the MPU for load sharing.

The MPUs cannot forward requests to the CPUS.

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7.3 Load Sharing on the User Plane

7.3.1 Overview

The RNC measures the following aspects of the DSP processing capability:

GBR capability of the DSP (DSP resources used for service access procedures are measured as GBRs for each service)

Processing capability of the DSP CPU

Accordingly, the RNC measures the user-plane load of a subrack with the following:

Total GBRs consumed by admitted services on the DSPs (GBR consumption)

Average CPU usage of all DSP CPUs in a subrack (CPU load)

The remaining GBRs of a subrack refer to the total DSP GBR capabilities of the subrack minus GBR consumption in the subrack. The remaining CPU processing capability of a subrack is the average CPU processing capability of all DSPs in the subrack minus the CPU load.

7.3.2 Procedure for Load Sharing on the User Plane

When user-plane resources need to be allocated to a new user, the MPU in the current subrack determines whether to allocate resources in the current subrack or forward the resource request to another subrack based on the GBR consumption and CPU load. Figure 7-5 shows the procedure for load sharing on the user plane.

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Figure 7-5 Load sharing on the user plane

Step 1 The MPU receives a resource allocation request from the CPUS.

Step 2 The MPU uses the user-plane load on the current subrack to determine whether to perform load sharing.

− If GBR consumption in the current subrack is equal to or lower than UserPlnSharingOutThd and the CPU load on the current subrack is less than or equal to UserPlnCpuSharingOutThd, the MPU in the current subrack attempts to allocate user-plane resources to the user in the current subrack. Substep 1 starts.

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− Otherwise, the MPU forwards the request to the MPU in the subrack with the lightest load, known as the target subrack. The MPU of this subrack will determine whether load sharing can be performed. Step 3 starts.

1. The MPU in the current subrack determines whether resources can be allocated.

If... Then...

The MPU finds in the current subrack the DSP with the lowest GBR consumption that also has a CPU load below DSPRestrainCpuThd

The MPU selects this DSP as the target DSP, and substep 2 starts.

The MPU cannot find such a DSP The RNC rejects the service access.

2. The target DSP allocates user-plane resources to the user.

Step 3 The target MPU determines whether load sharing can be performed.

1. If either of the following conditions is met, substep 2 starts:

− GBR consumption in the current subrack > UserPlnSharingOutThd, and remaining GBRs in the current subrack x (1 + UserPlnSharingOutOffset) < remaining GBRs in the target subrack

− CPU load in the current subrack > UserPlnCpuSharingOutThd, and the remaining CPU processing capability in the current subrack x (1 + UserPlnCpuSharingOutOffset) < remaining CPU processing capability in the target subrack.

If neither of these conditions is met, load sharing fails, and the MPU in the current subrack selects a DSP from the current subrack for resource allocation.

2. The MPU in the target subrack determines whether resources can be allocated.

If... Then...

The MPU in the target subrack finds in the target subrack a DSP whose GBR consumption is the lowest and whose CPU load is lower than DSPRestrainCpuThd

This DSP is selected as the target DSP, and substep 3 starts.

The MPU in the target subrack cannot find such a DSP The RNC rejects the service access.

3. The target DSP allocates user-plane resources to the user.

The SET UUSERPLNSHAREPARA command configures thresholds for load sharing on the user plane.

Load sharing is considered yielding noticeable effects if the load is balanced across the CPUs of the MPUs. To check the CPU load on an MPU, run the DSP CPUUSAGE command. If the load is not balanced, consult Huawei engineers to adjust the thresholds for load sharing or adjust the configuration of DPUs in the subracks.

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Flow Control 8 Engineering Guidelines



8-1

8 Engineering Guidelines

8.1 Access Control and Domain-Specific Access Control

8.1.1 Factors That Affect Access control and Domain-Specific Access Control

Whether access control or DSAC yields noticeable effects depends on the following factors:

How the operator defines users

If SIM cards are evenly distributed among ACs before being sold, access control or DSAC can yield noticeable effects. If SIM cards are unevenly or incorrectly distributed among ACs, do not enable access control or DSAC because it may fail to yield noticeable effects.

UE compliance

DSAC is applicable only to UEs that comply with 3GPP Release 6 or later. Access control is applicable to all UEs.

After access control or DSAC is enabled, run the DSP UCELLACR or DSP UCELLDSAC command, respectively, to check the running status. To find out whether access control is creating noticeable effects, check the value of the counter VS.RRC.AttConnEstab.Msg. Assuming AcRstrctPercent is set to 20%, access control is yielding noticeable effects if the value of this counter is 20% less than its value before access control was enabled.

8.1.2 Configuration Principles and Suggestions

Enable DSAC PS ahead of mass gatherings and disable it afterwards.

Enable access control or DSAC PS according to the values of the related counters.

− Check the RRC setup success rate of the cell. If the value of this KPI is significantly lower than it was on the same day last week, check the value of VS.RRC.FailConnEstab.NoReply.

− RRC setup success rate = RRC.SuccConnEstab.sum/VS.RRC.AttConnEstab.Sum

− If VS.RRC.FailConnEstab.NoReply is significantly higher than it was on the same day last week, check the value of VS.MeanRTWP.

− If VS.MeanRTWP is significantly higher than it was on the same day last week, check the value of VS.RRC.AttConnEstab.Sum.

− If VS.RRC.AttConnEstab.Sum is significantly higher than it was the same day last week, the low RRC setup success rate has been caused by heavy traffic. In this case, enable DSAC PS to alleviate the traffic impact.

− If the RRC setup success rate is still low, enable access control.

To enable DSAC PS, set PsRestriction to TRUE and AcRestriction to the number of ACs on which DSAC is performed.

To enable access control, set AcRstrctSwitch to ON and AcRstrctPercent to the number of ACs on which access control is performed.

After access control or DSAC PS is enabled, observe the value of VS.RRC.AttConnEstab.Sum, which indicates the number of RRC setup attempts. If the value of this counter keeps decreasing, the network is not subject to traffic impacts anymore and you can disable access control and DSAC PS.

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8.1.3 Performance Optimization

If access control or DSAC fails to yield the expected effects, change the number of ACs on which access control or DSAC is performed. It is recommended that this value be adjusted in steps of 10%.

8.1.4 Key Parameter Settings

Increasing the number of ACs on which access control or DSAC is performed decreases the number of RRC setup requests and increases the RRC setup success rate. Decreasing the number of ACs on which access control or DSAC is performed increases the number of RRC setup requests and decreases the RRC setup success rate.

8.2 Queue-based RRC Shaping

8.2.1 Factors That Affect Queue-based RRC Shaping

During mass gatherings, CPU usage soars and fluctuates with changes in traffic volume. When CPU usage exceeds the critical threshold (90%), the RRC and RAB setup success rates decrease. In this case, enable queue-based RRC shaping, which stabilizes the influx of RRC connection requests into the system. This stabilizes the CPU usage and increases RRC and RAC setup success rates.

Once queue-based RRC shaping is enabled, the load-sharing threshold and the parameters for other flow control functions that affect the CPU usage (such as CAPS control) need to be adjusted.


Enable queue-based RRC shaping ahead of mass gatherings. At the same time, increase the values of the parameters for flow control functions that affect the CPU usage. Contact Huawei technical support to determine a detailed plan.

8.3 CAPS Control

8.3.1 Factors That Affect CAPS Control

The effect of CAPS control depends on the accuracy of the estimation of the allowed number of RRC connection requests in the cell. If the allowed number of RRC connection requests is too large, CAPS control cannot yield noticeable effects. If the allowed number of RRC connection requests is too small, resources may not be fully utilized. The SET UCALLSHOCKCTRL command configures the allowed number of RRC connection requests per second in a cell. Contact Huawei technical support to adjust this number.


Check the value of VS.RRC.AttConnEstab.Sum. If the value is significantly higher than it was on the same day last week and the service setup success rate is low, it is recommended that CAPS control be enabled.

CS service setup success rate = (VS.RAB.SuccEstabCS.Conv + VS.RAB.SuccEstabCS.Str)/(VS.RAB.AttEstabCS.Conv + VS.RAB.AttEstabCS.Str)

PS service setup success rate = (VS.RAB.SuccEstabPS.Conv + VS.RAB.SuccEstabPS.Str + VS.RAB.SuccEstabPS.Int + VS.RAB.SuccEstabPS.Bkg)/(VS.RAB.AttEstabPS.Conv + VS.RAB.AttEstabPS.Str + VS.RAB.AttEstabPS.Int + VS.RAB.AttEstabPS.Bkg)

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8-3

8.3.3 Performance Optimization

Check the service setup success rate of the cell. If the service-setup success rate is low, run the SET UCALLSHOCKCTRL command to reduce the allowed number of RRC connection requests per second in the cell. The minimum number is 2. If the service-setup success rate is high, run the SET UCALLSHOCKCTRL command.

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Flow Control 9 Parameters



9-1

9 Parameters

Table 9-1 Parameter description

Parameter ID NE MML Command Description

SMWINDOW BSC6900 SET FCMSGQTHD(Optional) Meaning: Number of message block occupancy rate samples involved in the calculation of the average CPU usage in the sliding window GUI Value Range: 2~2000 Actual Value Range: 2~2000 Unit: None Default Value: 10

CTHD BSC6900 SET FCMSGQTHD(Optional) Meaning: Critical threshold of packet queue usage. When the packet queue usage reaches or exceeds the threshold, all active flow control functions are implemented. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 95

ACCTHD BSC6900 SET FCMSGQTHD(Optional) Meaning: Access packet recovery threshold. When the average packet queue usage of sliding windows is lower than the threshold, AC flow control is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 70

ACRTHD BSC6900 SET FCMSGQTHD(Optional) Meaning: Access packet recovery threshold. When the average packet queue usage of sliding windows is lower than the threshold, AC flow control is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 70

PAGESW BSC6900 SET FCSW(Optional) Meaning: Whether to control paging flow GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

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RsvdPara14 BSC6900 SET UDPUCFGDATA(Optional)

Meaning: This parameter is saved for the coming usage. GUI Value Range: 0~4294967295 Actual Value Range: 0~4294967295 Unit: None Default Value: 0



SMWINDOW BSC6900 SET FCCPUTHD(Optional) Meaning: Number of CPU usage samples involved in the calculation of the average CPU usage in the sliding window GUI Value Range: 2~2000 Actual Value Range: 2~2000 Unit: None Default Value: 10

FDWINDOW BSC6900 SET FCCPUTHD(Optional) Meaning: Number of CPU usage sampling times for fast judgment. The value of this parameter must be of half size of "Filter window" or smaller. GUI Value Range: 1~1000 Actual Value Range: 1~1000 Unit: None Default Value: 4

CTHD BSC6900 SET FCCPUTHD(Optional) Meaning: Critical threshold of CPU usage. When the CPU usage in "Fast judgement window" reaches or exceeds the threshold, all active flow control functions are implemented. Otherwise, the corresponding flow control mechanism is used. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 95

FCSW BSC6900 SET FCSW(Mandatory) Meaning: Flow control switch. Other switches are valid only when "Flow control switch" is "ON". GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None

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Default Value: ON

ACCTHD BSC6900 SET FCCPUTHD(Optional) Meaning: Access flow control threshold. When the average CPU usage of sliding windows exceeds the threshold, AC flow control is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 80

AcIntervalOfCell

BSC6900 SET UACALGO(Mandatory) Meaning: Interval of automatic access classes restriction between cells. When a subsystem of an RNC performs access classes restriction on cells managed by this subsystem, it selects the first cell at random. After waiting for the time specified in this parameter, the subsystem selects the second cell and the first cell is still with access classes restriction. The process lasts until all the cells are going through access classes restriction. For detailed information of this parameter, refer to 3GPP TS 22.011. GUI Value Range: 1~36000 Actual Value Range: 10~360000, step:10 Unit: ms Default Value: 50

AcRstrctIntervalLen

BSC6900 SET UACALGO(Mandatory) Meaning: Interval of access classes restriction. When a cell performs access classes restriction, it selects some access classes and after the restriction on these access classes lasts for the time specified in this parameter, the access classes restriction is released and the cell selects other access classes for restriction. GUI Value Range: 6~3600 Actual Value Range: 6~3600 Unit: s Default Value: 10

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AcRstrctPercent

BSC6900 SET UACALGO(Mandatory) Meaning: Access restriction ratio. When a cell performs access classes restriction, you can select some access classes from AC0 to AC9 based on the ratio specified in this parameter and perform access classes restriction on the selected access classes. After access classes restriction goes on for AcRstrctIntervalLen, the original access classes restriction is released and other access classes of the local cell are selected for access classes restriction based on the ratio specified in this parameter. GUI Value Range: 1~10 Actual Value Range: 0.1~1, step:0.1 Unit: % Default Value: 2

ACRTHD BSC6900 SET FCCPUTHD(Optional) Meaning: Access flow control recovery threshold. When the average CPU usage of sliding windows is lower than the threshold, AC flow control is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 70

ACSW BSC6900 SET FCSW(Optional) Meaning: Whether to control AC flow GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

AcRstrctSwitch

BSC6900 SET UACALGO(Optional) Meaning: OFF indicates that the AC algorithm is automatically disabled. ON indicates that the AC algorithm is automatically enabled. GUI Value Range: OFF, ON Actual Value Range: OFF, ON Unit: None Default Value: OFF

PAGESW BSC6900 SET FCSW(Optional) Meaning: Whether to control paging flow GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

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CPAGECTHD BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging flow control over real-time services. BE services uses the same paging flow control thresholds as SS and LCS to ensure the paging success rate of real-time services. When the average CPU usage within several sliding windows reaches or exceeds "Call page restore threshold", the linear paging flow control on real-time services is started. When the average CPU usage within several sliding windows reaches or exceeds "Call page control threshold", the 100% paging flow control on real-time services is started. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 90

SLPAGECTHD

BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging flow control over best effort (BE) services, supplementary services (SS), and the location service (LCS). BE services uses the same paging flow control thresholds as SS and LCS to ensure the paging success rate of real-time services. When the average CPU usage within several sliding windows reaches or exceeds "SS and LCS page restore threshold", the linear paging flow control on BE services, SS, and LCS is started. When the average CPU usage within several sliding windows reaches or exceeds "SS and LCS page control threshold", the 100% paging flow control on BE services, SS, and LCS is started. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 80

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SMPAGECTHD

BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging flow control over the short message service (SMS). When the average CPU usage within several sliding windows reaches or exceeds "SMS page restore threshold", the linear paging flow control on SMS is started. When the average CPU usage within several sliding windows reaches or exceeds the "SMS page control threshold", the 100% paging flow control on SMS is started. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 70

CPAGERTHD BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging control over real-time services. BE services uses the same paging flow control thresholds as SS and LCS to ensure the paging success rate of real-time services. When the average CPU usage within several sliding windows reaches or exceeds "Call page restore threshold", the linear paging flow control on real-time services is started. When the average CPU usage within several sliding windows is lower than "Call page restore threshold", paging control over real-time services is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 75

SLPAGERTHD

BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging flow control over best effort (BE) services, supplementary services (SS), and location service (LCS). BE services uses the same paging flow control thresholds as SS and LCS to ensure the paging success rate of real-time services. When the average CPU usage within several sliding windows reaches or exceeds "SS and LCS page restore threshold", the linear paging flow control on BE services, SS, and LCS is started. When the average CPU usage within several sliding windows is lower than the "SS and LCS page restore threshold", paging flow control over BE services, SS, and LCS is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100

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9-7


Unit: % Default Value: 70

SMPAGERTHD

BSC6900 SET FCCPUTHD(Optional) Meaning: CPU usage threshold for paging flow control over the short message service (SMS). When the average CPU usage within several sliding windows reaches or exceeds "SMS page restore threshold", the linear paging flow control on SMS is started. When the average CPU usage within several sliding windows is lower than "SMS page restore threshold", the flow control on SMS is stopped. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 60

SysRrcRejNum

BSC6900 SET UCALLSHOCKCTRL(Optional)

Meaning: The parameter specifies the maximum number of RRC Connection Reject messages per second from SPU subsystem to UE. When the SPU subsystem is in flow control state, the system will respond RRC Connection Reject message to UE. If the number of RRC Connection Reject messages exceeds the value of the parameter, RNC will discard the RRC connection request. GUI Value Range: 1~500 Actual Value Range: 1~500 Unit: None Default Value: 100

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CRRCCONNCCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for stopping load sharing on call service RRC connection setup requests. When the CPU usage of an XPU subsystem reaches this threshold or CtrlPlnSharingOutThd, whichever is smaller, later call service RRC connection setup requests will be carried by other XPU subsystems. CtrlPlnSharingOutThd is set by using the command "SET UCTRLPLNSHAREPARA". If the CPU usage of all candidate XPU subsystems exceeds this threshold, flow control on call service RRC connection setup requests is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 85

CRRCCONNRCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for recoverying load sharing on call service RRC connection setup requests. If the CPU usage of an XPU subsystem is lower than this threshold, this XPU subsystem is the candidate subsystem for the load sharing on call service RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 75

CRRCCONNCMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for stopping load sharing on call service RRC connection setup requests. When the packet usage of an XPU subsystem reaches this threshold, later call service packets will be carried by other XPU subsystems. If the packet usage of all candidate XPU subsystems exceeds this threshold, flow control on call service RRC connection setup request packets is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 75

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CRRCCONNRMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for recoverying load sharing on call service RRC connection setup requests. When the packet usage of an XPU subsystem is lower than this threshold, this XPU subsystem is a candidate subsystem for load sharing on call service RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 65

LRRCCONNCCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for stopping load sharing on location service RRC connection setup requests. When the CPU usage of an XPU subsystem reaches this threshold or CtrlPlnSharingOutThd, whichever is smaller, later location service RRC connection setup requests will be carried by other XPU subsystems. CtrlPlnSharingOutThd is set by using the command "SET UCTRLPLNSHAREPARA". If the CPU usage of all candidate XPU subsystems exceeds this threshold, flow control on location service RRC connection setup requests is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 90

LRRCCONNRCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for recoverying load sharing on location service RRC connection setup requests. If the CPU usage of an XPU subsystem is lower than this threshold, this XPU subsystem is the candidate subsystem for load sharing on location service RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 80

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LRRCCONNCMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for stopping load sharing on location service RRC connection setup requests. When the packet usage of an XPU subsystem reaches this threshold, later call service packets will be carried by other XPU subsystems. If the packet usage of all candidate XPU subsystems exceeds this threshold, flow control on location service RRC connection setup request packets is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 75

LRRCCONNRMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for recoverying load sharing on location service RRC connection setup requests. When the packet usage of an XPU subsystem is lower than this threshold, this XPU subsystem is a candidate subsystem for load sharing on location service RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 65

SMRRCCONNCCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for stopping load sharing on SMS RRC connection setup requests. When the CPU usage of an XPU subsystem reaches this threshold or CtrlPlnSharingOutThd, whichever is smaller, later SMS RRC connection setup requests will be carried by other XPU subsystems. CtrlPlnSharingOutThd is set by using the command "SET UCTRLPLNSHAREPARA". If the CPU usage of all candidate XPU subsystems exceeds this threshold, flow control on SMS RRC connection setup requests is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 70

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SMRRCCONNRCPUTHD

BSC6900 SET SHARETHD(Optional) Meaning: CPU usage threshold for recoverying load sharing on SMS RRC connection setup requests. If the CPU usage of an XPU subsystem is lower than this threshold, this XPU subsystem is a candidate subsystem for the load sharing on SMS RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 60

SMRRCCONNCMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for stopping load sharing on SMS RRC connection setup requests. When the packet usage of an XPU subsystem reaches this threshold, later SMS packets will be carried by other XPU subsystems. If the packet usage of all candidate XPU subsystems exceeds this threshold, flow control on SMS RRC connection setup request packets is triggered. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 75

SMRRCCONNRMSGTHD

BSC6900 SET SHARETHD(Optional) Meaning: Packet usage threshold for recoverying load sharing on SMS RRC connection setup requests. When the packet usage of an XPU subsystem is lower than this threshold, this XPU subsystem is a candidate subsystem for load sharing on SMS RRC connection setup requests. GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 65

IURULSW BSC6900 SET FCSW(Optional) Meaning: Whether to control the traffic on the Iur uplink GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

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IURDLSW BSC6900 SET FCSW(Optional) Meaning: Whether to control the traffic on the Iur downlink GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

CBSSW BSC6900 SET FCSW(Optional) Meaning: Whether to control CBS flow GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

CELLURASW BSC6900 SET FCSW(Optional) Meaning: Whether to control cell updates GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

IURGSW BSC6900 SET FCSW(Optional) Meaning: Whether to control traffic on the Iur-g interface GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

RSVDPARA1 BSC6900 SET TRANSPATCHPARA(Optional)

Meaning: Parameter 1 reserved for future use. GUI Value Range: OFF(OFF), ON(ON) Actual Value Range: OFF, ON Unit: None Default Value: None

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RsvdPara1 BSC6900 SET UCACALGOSWITCH(Optional)

Meaning: Reserved Parameter1. GUI Value Range: RSVDBIT1(Reserved Switch 1), RSVDBIT2(Reserved Switch 2), RSVDBIT3(Reserved Switch 3), RSVDBIT4(Reserved Switch 4), RSVDBIT5(Reserved Switch 5), RSVDBIT6(Reserved Switch 6), RSVDBIT7(Reserved Switch 7), RSVDBIT8(Reserved Switch 8), RSVDBIT9(Reserved Switch 9), RSVDBIT10(Reserved Switch 10), RSVDBIT11(Reserved Switch 11), RSVDBIT12(Reserved Switch 12), RSVDBIT13(Reserved Switch 13), RSVDBIT14(Reserved Switch 14), RSVDBIT15(Reserved Switch 15), RSVDBIT16(Reserved Switch 16) Actual Value Range: RSVDBIT1, RSVDBIT2, RSVDBIT3, RSVDBIT4, RSVDBIT5, RSVDBIT6, RSVDBIT7, RSVDBIT8, RSVDBIT9, RSVDBIT10, RSVDBIT11, RSVDBIT12, RSVDBIT13, RSVDBIT14, RSVDBIT15, RSVDBIT16 Unit: None Default Value: None

RsvdPara1 BSC6900 ADD UCNNODE(Optional) MOD UCNNODE(Optional)

Meaning: Reserved parameter 1. GUI Value Range: RSVDBIT1_BIT1, RSVDBIT1_BIT2, RSVDBIT1_BIT3, RSVDBIT1_BIT4, RSVDBIT1_BIT5, RSVDBIT1_BIT6, RSVDBIT1_BIT7, RSVDBIT1_BIT8, RSVDBIT1_BIT9, RSVDBIT1_BIT10, RSVDBIT1_BIT11, RSVDBIT1_BIT12, RSVDBIT1_BIT13, RSVDBIT1_BIT14, RSVDBIT1_BIT15, RSVDBIT1_BIT16, RSVDBIT1_BIT17, RSVDBIT1_BIT18, RSVDBIT1_BIT19, RSVDBIT1_BIT20, RSVDBIT1_BIT21, RSVDBIT1_BIT22, RSVDBIT1_BIT23, RSVDBIT1_BIT24, RSVDBIT1_BIT25, RSVDBIT1_BIT26, RSVDBIT1_BIT27, RSVDBIT1_BIT28, RSVDBIT1_BIT29, RSVDBIT1_BIT30, RSVDBIT1_BIT31, RSVDBIT1_BIT32 Actual Value Range: Each bit can be set ON or OFF Unit: None Default Value: None

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RsvdPara1 BSC6900 ADD UNRNC(Optional) MOD UNRNC(Optional)

Meaning: Reserved parameter 1. GUI Value Range: RSVDBIT1_BIT1, RSVDBIT1_BIT2, RSVDBIT1_BIT3, RSVDBIT1_BIT4, RSVDBIT1_BIT5, RSVDBIT1_BIT6, RSVDBIT1_BIT7, RSVDBIT1_BIT8, RSVDBIT1_BIT9, RSVDBIT1_BIT10, RSVDBIT1_BIT11, RSVDBIT1_BIT12, RSVDBIT1_BIT13, RSVDBIT1_BIT14, RSVDBIT1_BIT15, RSVDBIT1_BIT16, RSVDBIT1_BIT17, RSVDBIT1_BIT18, RSVDBIT1_BIT19, RSVDBIT1_BIT20, RSVDBIT1_BIT21, RSVDBIT1_BIT22, RSVDBIT1_BIT23, RSVDBIT1_BIT24, RSVDBIT1_BIT25, RSVDBIT1_BIT26, RSVDBIT1_BIT27, RSVDBIT1_BIT28, RSVDBIT1_BIT29, RSVDBIT1_BIT30, RSVDBIT1_BIT31, RSVDBIT1_BIT32 Actual Value Range: This parameter is set to 0 or 1 according to the related domains. Unit: None Default Value: None

T300 BSC6900 SET UIDLEMODETIMER(Optional)

Meaning: T300 is started when UE sends the RRC CONNECTION REQUEST message. It is stopped when UE receives the RRC CONNECTION SETUP message. RRC CONNECTION REQUEST will be resent upon the expiry of the timer if V300 is lower than or equal to N300, else enter idle mode. GUI Value Range: D100, D200, D400, D600, D800, D1000, D1200, D1400, D1600, D1800, D2000, D3000, D4000, D6000, D8000 Actual Value Range: 100, 200, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 3000, 4000, 6000, 8000 Unit: ms Default Value: D2000

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SwitchParameter1

BSC6900 SET SS7PATCHSWITCH(Optional)

Meaning: Set patch switch parameter1 GUI Value Range: OFF(OFF), ON(ON) Actual Value Range: OFF, ON Unit: None Default Value: OFF

SSDSPAVEUSAGEALMTHD

BSC6900 SET CPUTHD(Optional) Meaning: DSP usage alarm clearance threshold. When the DSP usage is lower than the threshold, the DSP usage alarm is cleared. "DSP occupancy alarm clearance threshold" must be smaller than "DSP occupancy alarm threshold". GUI Value Range: 20~99 Actual Value Range: 20~99 Unit: % Default Value: 80

SSDSPMAXUSAGEALMTHD

BSC6900 SET CPUTHD(Optional) Meaning: DSP usage alarm threshold. When the DSP usage exceeds the threshold, a DSP usage alarm is reported. "DSP occupancy alarm clearance threshold" must be smaller than "DSP occupancy alarm threshold". GUI Value Range: 30~100 Actual Value Range: 30~100 Unit: % Default Value: 85

RrcConnRejWaitTmr

BSC6900 SET USTATETIMER(Optional) Meaning: Wait time in RRC connection reject message, the time period the UE has to wait before repeating the rejected procedure of RRC connection GUI Value Range: 0~15 Actual Value Range: 0~15 Unit: s Default Value: 4

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CallShockCtrlSwitch


Meaning: The parameter specifies whether to perform Call Attempt Per Second (CAPS) control for the number of RRC connection establishments at SPU subsystem level, NodeB level, or cell level. SYS_LEVEL indicates that the RNC will perform flow control for the RRC connection requests at SPU subsystem level. NODEB_LEVEL indicates that the RNC will perform flow control for the RRC connection requests at NodeB level. CELL_LEVEL indicates that the RNC will perform flow control for the RRC connection requests at cell level. GUI Value Range: SYS_LEVEL(SYS_LEVEL), NODEB_LEVEL(NODEB_LEVEL), CELL_LEVEL(CELL_LEVEL) Actual Value Range: SYS_LEVEL, NODEB_LEVEL, CELL_LEVEL Unit: None Default Value: None

CallShockJudgePeriod


Meaning: The parameter specifies the period of entering flow control at SPU subsystem level, NodeB level, or cell level. In the period, if the number of RRC connection requests that the SPU subsystem, NodeB, or cell receives exceed relative trigger threshold (the threshold can be set by "SysTotalRrcNumThd", "NBTotalRrcNumThd", or "CellTotalRrcNumThd"), RNC will perform flow control for the RRC establishment request. GUI Value Range: 1~5 Actual Value Range: 1~5 Unit: s Default Value: 3

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CellTotalRrcNumThd


Meaning: The parameter specifies the threshold of entering flow control for RRC connection requests at cell level. During the call shock judgment period (CallShockJudgePeriod), when the number of RRC connection requests exceed the value of the parameter, RNC will perform flow control. The flow control strategies for RRC connection requests are as follows: If the originating interactive call, originating background call, or originating streaming call causes the RRC connection requests, RNC will perform flow control directly. If the number of admitted RRC connection requests for registration and inter-RAT cell reselection exceeds the value of "CellHighPriRrcNum", RNC will perform flow control. If the number of admitted RRC connection requests for AMR exceeds the value of "CellAmrRrcNum", RNC will perform flow control. If other services cause RRC connection requests, RNC will not perform flow control. GUI Value Range: 1~100 Actual Value Range: 1~100 Unit: None Default Value: 45

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NBTotalRrcNumThd


Meaning: The parameter specifies the threshold of entering flow control for RRC connection requests at NodeB level. During the call shock judgment period (CallShockJudgePeriod), when the number of RRC connection requests exceed the value of the parameter, RNC will perform flow control. The flow control strategies for RRC connection requests are as follows: If the originating interactive call, originating background call, or originating streaming call causes the RRC connection requests, RNC will perform flow control directly. If the number of admitted RRC connection requests for registration and inter-RAT cell reselection exceeds the value of "NBHighPriRrcNum", RNC will perform flow control. If the number of admitted RRC connection requests for AMR exceeds the value of "NBAmrRrcNum", RNC will perform flow control. If other services cause RRC connection requests, RNC will not perform flow control. GUI Value Range: 1~200 Actual Value Range: 1~200 Unit: None Default Value: 60

CellAmrRrcNum


Meaning: The parameter specifies the number of RRC connection requests per second for originating conversational call at cell level. GUI Value Range: 1~100 Actual Value Range: 1~100 Unit: None Default Value: 15

NBAmrRrcNum


Meaning: The parameter specifies the number of RRC connection requests per second for originating conversational call at NodeB level. GUI Value Range: 1~200 Actual Value Range: 1~200 Unit: None Default Value: 20

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RegByFachSwitch


Meaning: The parameter specifies whether to set up RRC connection for registration on the FACH instead of on the DCH in the call shock. When ON is selected, RNC will perform flow control at cell level or NodeB level, the RRC connection for registration is set up on the FACH instead of on the DCH. When OFF is selected, the channel setup strategy of RRC connection request for registration can be set by running the SET URRCESTCAUSE command. GUI Value Range: OFF, ON Actual Value Range: OFF, ON Unit: None Default Value: ON

CellHighPriRrcNum


Meaning: The parameter specifies the number of RRC connection requests per second for registration and inter-RAT cell reselection at cell level. GUI Value Range: 1~100 Actual Value Range: 1~100 Unit: None Default Value: 15

NBHighPriRrcNum


Meaning: The parameter specifies the number of RRC connection requests per second for registration and inter-RAT cell reselection at NodeB level. GUI Value Range: 1~200 Actual Value Range: 1~200 Unit: None Default Value: 20

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ReservedSwitch0

BSC6900 SET UCORRMALGOSWITCH(Optional)

Meaning: CORRM algorithm reserved switch 0. The switch is reserved for further change request use. GUI Value Range: RESERVED_SWITCH_0_BIT1, RESERVED_SWITCH_0_BIT2, RESERVED_SWITCH_0_BIT3, RESERVED_SWITCH_0_BIT4, RESERVED_SWITCH_0_BIT5, RESERVED_SWITCH_0_BIT6, RESERVED_SWITCH_0_BIT7, RESERVED_SWITCH_0_BIT8, RESERVED_SWITCH_0_BIT9, RESERVED_SWITCH_0_BIT10, RESERVED_SWITCH_0_BIT11, RESERVED_SWITCH_0_BIT12, RESERVED_SWITCH_0_BIT13, RESERVED_SWITCH_0_BIT14, RESERVED_SWITCH_0_BIT15, RESERVED_SWITCH_0_BIT16, RESERVED_SWITCH_0_BIT17, RESERVED_SWITCH_0_BIT18, RESERVED_SWITCH_0_BIT19, RESERVED_SWITCH_0_BIT20, RESERVED_SWITCH_0_BIT21, RESERVED_SWITCH_0_BIT22, RESERVED_SWITCH_0_BIT23, RESERVED_SWITCH_0_BIT24, RESERVED_SWITCH_0_BIT25, RESERVED_SWITCH_0_BIT26, RESERVED_SWITCH_0_BIT27, RESERVED_SWITCH_0_BIT28, RESERVED_SWITCH_0_BIT29, RESERVED_SWITCH_0_BIT30, RESERVED_SWITCH_0_BIT31, RESERVED_SWITCH_0_BIT32 Actual Value Range: RESERVED_SWITCH_0_BIT1, RESERVED_SWITCH_0_BIT2, RESERVED_SWITCH_0_BIT3, RESERVED_SWITCH_0_BIT4, RESERVED_SWITCH_0_BIT5, RESERVED_SWITCH_0_BIT6, RESERVED_SWITCH_0_BIT7, RESERVED_SWITCH_0_BIT8, RESERVED_SWITCH_0_BIT9, RESERVED_SWITCH_0_BIT10, RESERVED_SWITCH_0_BIT11, RESERVED_SWITCH_0_BIT12, RESERVED_SWITCH_0_BIT13, RESERVED_SWITCH_0_BIT14, RESERVED_SWITCH_0_BIT15,

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RESERVED_SWITCH_0_BIT16, RESERVED_SWITCH_0_BIT17, RESERVED_SWITCH_0_BIT18, RESERVED_SWITCH_0_BIT19, RESERVED_SWITCH_0_BIT20, RESERVED_SWITCH_0_BIT21, RESERVED_SWITCH_0_BIT22, RESERVED_SWITCH_0_BIT23, RESERVED_SWITCH_0_BIT24, RESERVED_SWITCH_0_BIT25, RESERVED_SWITCH_0_BIT26, RESERVED_SWITCH_0_BIT27, RESERVED_SWITCH_0_BIT28, RESERVED_SWITCH_0_BIT29, RESERVED_SWITCH_0_BIT30, RESERVED_SWITCH_0_BIT31, RESERVED_SWITCH_0_BIT32 Unit: None Default Value: None

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ReservedSwitch1


Meaning: CORRM algorithm reserved switch 1. The switch is reserved for further change request use. GUI Value Range: RESERVED_SWITCH_1_BIT1, RESERVED_SWITCH_1_BIT2, RESERVED_SWITCH_1_BIT3, RESERVED_SWITCH_1_BIT4, RESERVED_SWITCH_1_BIT5, RESERVED_SWITCH_1_BIT6, RESERVED_SWITCH_1_BIT7, RESERVED_SWITCH_1_BIT8, RESERVED_SWITCH_1_BIT9, RESERVED_SWITCH_1_BIT10, RESERVED_SWITCH_1_BIT11, RESERVED_SWITCH_1_BIT12, RESERVED_SWITCH_1_BIT13, RESERVED_SWITCH_1_BIT14, RESERVED_SWITCH_1_BIT15, RESERVED_SWITCH_1_BIT16, RESERVED_SWITCH_1_BIT17, RESERVED_SWITCH_1_BIT18, RESERVED_SWITCH_1_BIT19, RESERVED_SWITCH_1_BIT20, RESERVED_SWITCH_1_BIT21, RESERVED_SWITCH_1_BIT22, RESERVED_SWITCH_1_BIT23, RESERVED_SWITCH_1_BIT24, RESERVED_SWITCH_1_BIT25, RESERVED_SWITCH_1_BIT26, RESERVED_SWITCH_1_BIT27, RESERVED_SWITCH_1_BIT28, RESERVED_SWITCH_1_BIT29, RESERVED_SWITCH_1_BIT30, RESERVED_SWITCH_1_BIT31, RESERVED_SWITCH_1_BIT32 Actual Value Range: RESERVED_SWITCH_1_BIT1, RESERVED_SWITCH_1_BIT2, RESERVED_SWITCH_1_BIT3, RESERVED_SWITCH_1_BIT4, RESERVED_SWITCH_1_BIT5, RESERVED_SWITCH_1_BIT6, RESERVED_SWITCH_1_BIT7, RESERVED_SWITCH_1_BIT8, RESERVED_SWITCH_1_BIT9, RESERVED_SWITCH_1_BIT10, RESERVED_SWITCH_1_BIT11, RESERVED_SWITCH_1_BIT12, RESERVED_SWITCH_1_BIT13, RESERVED_SWITCH_1_BIT14, RESERVED_SWITCH_1_BIT15,

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9-23


RESERVED_SWITCH_1_BIT16, RESERVED_SWITCH_1_BIT17, RESERVED_SWITCH_1_BIT18, RESERVED_SWITCH_1_BIT19, RESERVED_SWITCH_1_BIT20, RESERVED_SWITCH_1_BIT21, RESERVED_SWITCH_1_BIT22, RESERVED_SWITCH_1_BIT23, RESERVED_SWITCH_1_BIT24, RESERVED_SWITCH_1_BIT25, RESERVED_SWITCH_1_BIT26, RESERVED_SWITCH_1_BIT27, RESERVED_SWITCH_1_BIT28, RESERVED_SWITCH_1_BIT29, RESERVED_SWITCH_1_BIT30, RESERVED_SWITCH_1_BIT31, RESERVED_SWITCH_1_BIT32 Unit: None Default Value: None

ReservedU32Para1


Meaning: CORRM algorithm reserved U32 para 1. The para of 32 bits is reserved for further change request use. GUI Value Range: 0~4294967295 Actual Value Range: 0~4294967295 Unit: None Default Value: 4294967295

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9-24


T381 BSC6900 SET UCONNMODETIMER(Optional)

Meaning: T381 is started after the RNC send message "RRC CONNECTION SETUP"(or "CELL UPDATE CONFIRM"). If T381 expire and RNC does not receive "RRC CONNECTION SETUP COMPLETE"(or the response of "ELL UPDATE CONFIRM") and V381 is smaller than N381, RNC resend "RRC CONNECTION SETUP"(or "CELL UPDATE CONFIRM") and restart timer T381 and increase V381. If RNC receive "RRC CONNECTION SETUP COMPLETE"(or the response of "CELL UPDATE CONFIRM"), T381 will be stopped. Default value is 600ms. GUI Value Range: D0, D100, D200, D300, D400, D500, D600, D700, D800, D900, D1000, D1200, D1500, D2000 Actual Value Range: 0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1500, 2000 Unit: ms Default Value: D600

IUFCSW BSC6900 SET FCSW(Optional) Meaning: Whether to control signaling traffic on the IU interface GUI Value Range: ON, OFF Actual Value Range: ON, OFF Unit: None Default Value: ON

IntrTmr BSC6900 SET UIUTIMERANDNUM(Optional)

Meaning: CN flow control timer (long). If the OVERLOAD message is not received in this period, the traffic volume will be increased by a degree. GUI Value Range: 15000~120000 Actual Value Range: 15000~120000 Unit: ms Default Value: 60000

IgorTmr BSC6900 SET UIUTIMERANDNUM(Optional)

Meaning: CN flow control timer (short). The OVERLOAD message received repeatedly in this period will be discarded. GUI Value Range: 5000~30000 Actual Value Range: 5000~30000 Unit: ms Default Value: 20000

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9-25


IUCTHD BSC6900 SET FCSW(Optional) Meaning: Maximum traffic rate for restriction in the case of congestion on the IU interface. This parameter is valid only when "Board Class" is "XPU". GUI Value Range: 0~100 Actual Value Range: 0~100 Unit: None Default Value: 70

CtrlPlnSharingOutOffset

BSC6900 SET UCTRLPLNSHAREPARA(Optional)

Meaning: The sharing offset should be added to the target subrack or subsystem. This parameter is used for preferable selection of the homing subrack and homing subsystem during call forwarding. GUI Value Range: 1~10 Actual Value Range: 0.01~0.1, step:0.01 Unit: % Default Value: 5

CtrlPlnSharingOutThd


Meaning: Forwarding threshold of control plane load sharing. When the CPU usage is between the sharing threshold and overload threshold, and call number in each second reaches "Sharing out capability middle load", new arrival call attempts will be shared out to other SPU subsystem. GUI Value Range: 0~100 Actual Value Range: 0~1, step:0.01 Unit: % Default Value: 50

MaxCAPSLowLoad


Meaning: Maximum numbers of incoming calls in one second when the load is lower than the forwarding threshold. When the CPU usage is lower than the sharing out threshold and overload threshold, and call numbers in each second reach the threshold, new arrival call attempts will be shared out to other SPU subsystem and none will be shared in this SPU subsystem. GUI Value Range: 0~255 Actual Value Range: 0~255 Unit: None Default Value: 150

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9-26


MaxCAPSMidLoad


Meaning: Maximum numbers of incoming calls in one second when the load exceeds the forwarding threshold. When the CPU usage is between the sharing out threshold and overload threshold, and call number in one second reaches the threshold, new arrival call attempts will be shared out to other SPU subsystem and none will be shared in this SPU subsystem. GUI Value Range: 0~255 Actual Value Range: 0~255 Unit: None Default Value: 100

UserPlnSharingOutThd

BSC6900 SET UUSERPLNSHAREPARA(Optional)

Meaning: Percentage of User Plane Sharing Out threshold.The range of this threshold is changed from {50~100} to {0~100} to facilitate load balancing between subracks. Because when this threshold is lower than 50, load sharing is easier to be triggered between subracks. GUI Value Range: 0~100 Actual Value Range: 0~100 Unit: None Default Value: 90

UserPlnCpuSharingOutThd


Meaning: The parameter is added to trigger the load sharing when the DSP CPU usage exceeds this threshold, thus achieving load balance between subracks. GUI Value Range: 0~100 Actual Value Range: {0~100} Unit: % Default Value: 100

UserPlnCpuSharingOutOffset


Meaning: The parameter is added to avoid ping-pong handovers during the load sharing triggered by DSP CPU usage. GUI Value Range: 5~20 Actual Value Range: 5~20 Unit: % Default Value: 5

DSPRestrainCpuThd


Meaning: The parameter is added to stop CPUS from assigning users to a DSP whose CPU usage has exceeded this threshold. GUI Value Range: 0~100 Actual Value Range: 0~100 Unit: %

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9-27


Default Value: 0

PsRestriction BSC6900 ADD UCELLDSACMANUALPARA(Mandatory) MOD UCELLDSACMANUALPARA(Optional)

Meaning: Specifies whether to impose the access restriction on the PS domain. GUI Value Range: FALSE, TRUE Actual Value Range: FALSE, TRUE Unit: None Default Value: None

FRTRJT NodeB SET CONGCTRLPARA Meaning: Control Plane Congestion First Reject Threshold GUI Value Range: 80~90 Actual Value Range: 80~90 Unit: % Default Value: 90

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Flow Control 10 Counters



10-1

10 Counters

For details, see the BSC6900 UMTS Performance Counter Reference.

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Flow Control 11 Glossary



11-1

11 Glossary For terms that appear in this document, see Glossary.

Glossary.htm

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Flow Control 12 References



12-1

12 References

[1] Load Control Feature Parameter Description

[2] Call Admission Control Feature Parameter Description

[3] DSAC Feature Parameter Description

[4] Common Radio Resource Management Feature Parameter Description

[5] Transmission Resource Management Feature Parameter Description

[6] Radio Bearers Feature Parameter Description

[7] State Transition Feature Parameter Description

Load%20Control.htm


DSAC.htm

Common%20Radio%20Resource%20Management.htm


Radio%20Bearers.htm


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Flow Control 13 Appendix: Flow Control Algorithms



13-1

13 Appendix: Flow Control Algorithms

The RNC uses three flow control algorithms for overloaded RNC units: the switch algorithm, linear algorithm, and hierarchical algorithm. Different algorithms are used for different services. These algorithms cannot be set on the LMT.

13.1 Switch Algorithm

The principles of the switch algorithm are as follows:

When the resource usage, such as the CPU usage or message block usage, exceeds the control threshold of a flow control item, flow control is performed.

When the resource usage is lower than the restoration threshold, flow control is not performed.

Figure 13-1 Switch algorithm

The following flow control functions use the switch algorithm: printing flow control, debugging flow control, performance monitoring flow control, logging flow control, resource audit flow control, access control, paging control, RRC flow control based on the CPU usage and message block, Iur flow control, CBS flow control, cell/URA update flow control, Iur-g flow control, and MR flow control.

13.2 Linear Algorithm

The principles of the linear algorithm are as follows:

When the resource usage is higher than the control threshold of a flow control item, flow control is performed.

When the resource usage is lower than the restore threshold of a flow control item, flow control is not performed.

When the resource usage is between the restoration threshold and the control threshold of a flow control item, the flow control level changes linearly with the resource usage.

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13-2

Figure 13-2 Linear algorithm

The flow control level of the linear algorithm, that is, the probability (P) of performing flow control, is calculated as follows:

P = (resource usage – restoration threshold) x 100% / (control threshold – restoration threshold)

Flow Control triggered by DSP CPU overload uses the liner algorithm.

13.3 Hierarchical Algorithm

The principles of the hierarchical algorithm are as follows:

When the resource usage is higher than the control threshold of a flow control item, flow control is performed.

When the resource usage is lower than the restoration threshold of a flow control item, flow control is not performed.

When resource usage is between the restoration threshold and the control threshold of a flow control item, the flow control level changes hierarchically with the resource usage.

Figure 13-3 Hierarchical algorithm

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13-3

The flow control level of the hierarchical algorithm is calculated as follows:

Flow control level = [(resource usage – restoration threshold) x total number of flow control grades for the flow control item / (control threshold – restoration threshold)]

The [ ] symbol indicates an integer value.

The total flow control grades for each flow control item are specified in the system software and cannot be set on the LMT. They vary according to the flow control items.

MPU overload backpressure uses the hierarchical algorithm.

131554606-Flow-Control

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