UMTS_ RLC and MAC Layer in Detail

8/11/2019 UMTS_ RLC and MAC Layer in Detail

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RADIO INTERFACE

PROTOCOLS


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7.1 Introduction

7.2 Protocol Architecture

7.3 The Medium Access Control Protocol

7.4 The Radio Link Control Protocol7.5 The Packet Data Convergence Protocol

7.6 The Broadcast/Multicast Control Protocol

7.7 Multimedia Broadcast Multicast Service

7.8 The Radio Resource Control Protocol


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7.1 INTRODUCTION

The protocol layers above

physical layer

Data Link Layer (Layer 2)

Network Layer (Layer 3)

In UTRA FDD radio interface,Layer 2 is split into sublayers

in control plane, Layer 2

contains two sub-layers

Medium Access Control

(MAC) protocolRadio Link Control (RLC)

protocol


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in user plane, in addition toMAC and RLC, two additional

service-dependent protocols

Packet Data Convergence

Protocol (PDCP)

Broadcast/Multicast ControlProtocol (BMC)

In UTRA FDD radio interface,

Layer 3 consists of one protocol

Radio Resource Control (RRC),

which belongs to control plane


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7.2 PROTOCOL ARCHITECTURE

Figure 7.1

shows the overall radio interface protocol architecture

contains only the protocols that are visible in UTRAN


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Physical layer

offers services to MAC layervia transport channels

transport channels arecharacterized by

how and with whatcharacteristics data istransferred

MAC layer

offers services to RLC layer bymeans of logical channels

logical channels arecharacterized by

what type of data istransmitted


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RLC layer offers services to higher

layers via service accesspoints (SAPs)

SAPs describe how the RLC

layer handles the datapackets and if, for example,the automatic repeat request(ARQ) function is used


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Automatic Repeat Request (ARQ)

protocol for dealing with data words that are corrupted

by errors whereby the receiving system requests a re-

transmission of the word(s) in error


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on the control planeRLC services are used

by RRC layer forsignaling transport

on the user plane

RLC services are usedby either of the following

the service-specificprotocol layers PDCPor BMC

other higher-layer u-plane functions (e.g.speech codec)


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RLC services

called Signaling Radio

Bearers (SRB) in the

control plane

called Radio Bearers inthe user plane

RLC protocol operates in

three modes

transparent mode

unacknowledged mode

acknowledged mode


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Packet DataConvergence Protocol

(PDCP)

exists only for PS

domain services

main function is header

compression

the services offered by

PDCP are called Radio

Bearers


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Broadcast Multicast Controlprotocol (BMC)

used to convey over the

radio interface messages

originating from Cell

Broadcast Centre Release99, the only

specified broadcasting

service is SMS Cell

Broadcast service, which

is derived from GSM

the service offered by

BMC protocol is also

called a Radio Bearer


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RRC layer offers services to higher

layers via service accesspoints (SAP), which are usedby

the higher layer protocols

in the UE side the Iu RANAP protocol in

the UTRAN side

all higher layer signaling(mobility management, callcontrol, session management,

etc.) is encapsulated intoRRC messages fortransmission over radiointerface

SIGNALING AND TRAFFIC


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SIGNALING AND TRAFFIC

CONNECTIONS BETWEEN MOBILE AND

SGSN


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The control interfaces betweenRRC and all the lower layer

protocols are used by RRC layer

to

configure characteristics of

the lower layer protocol

entities

including parameters for

the physical, transport and

logical channels

command the lower layers to

perform certain types ofmeasurement

report measurement

results and errors to RRC


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7.3 THE MEDIUM ACCESS CONTROL

PROTOCOL

In Medium Access Control (MAC) layer

logical channels are mapped to transport channels

MAC layer

responsible for selecting an appropriate transport format

(TF) for each transport channel depending on theinstantaneous source rate(s) of logical channels

the transport format is selected w.r.t the transport formatcombination set (TFCS) which is defined by theadmission control for each connection


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7.3.1 MAC Layer Architecture

7.3.2 MAC Functions

7.3.3 Logical Channels

7.3.4 Mapping Between Logical Channels andTransport Channels


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7.3.1 MAC LAYER ARCHITECTURE

Figure 7.2 shows the MAC layer logical architecture

MAC layer consists of three logical entities

MAC-b

MAC-c/sh

MAC-d


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MAC-b

handles the broadcast channel (BCH)

one MAC-b entity in each UE

one MAC-b in the UTRAN (located in Node B) for each cell


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MAC-c/sh handles the common channels and shared channels

Paging Channel (PCH)

Forward Link Access Channel (FACH)

Random Access Channel (RACH)

Uplink Common Packet Channel (CPCH)Downlink Shared Channel (DSCH)


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one MAC-c/sh entity in each UE that is using shared

channel(s)

one MAC-c/sh in the UTRAN (located in the controlling

RNC) for each cell

BCCH logical channel can be mapped to either BCH orFACH transport channel


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MAC-d

responsible for handling dedicated channels (DCH) allocated

to a UE in connected mode

one MAC-d entity in UE

one MAC-d entity in UTRAN (in the serving RNC) for eachUE


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7.3.2 MAC FUNCTIONS

Mapping

mapping between logical channels and transport channels

Transport Format selection

selection of appropriate Transport Format (from the

Transport Format Combination Set, TFCS) for each

Transport Channel, depending on the instantaneous source

rate


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Priority handling

priority handling between data flows of one UE

achieved by selecting highbit rate and lowbit rate

transport formats for different data flows

priority handling between UEs by means of dynamicscheduling

a dynamic scheduling function may be applied for

common and shared downlink transport channels FACH

and DSCH


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Identification of UEs on common transport channels

when a common transport channel (RACH, FACH or

CPCH) carries data from dedicated-type logical channels

(DCCH, DTCH), the identification of the UE (Cell Radio

Network Temporary Identity (C-RNTI) or UTRAN RadioNetwork Temporary Identity (U-RNTI)) is included in the

MAC header


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Multiplexing/demultiplexing of higher layer PDUs

into/from transport blocks delivered to/from the

physical layer on common transport channels

MAC handles service multiplexing for common transport

channels (RACH/FACH/CPCH)


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Multiplexing / demultiplexing of higher layer PDUsinto/from transport block sets delivered to/from the

physical layer on dedicated transport channels

MAC allows service multiplexing also for dedicated

transport channels MAC multiplexing is possible only for services with the

same QoS parameters

physical layer multiplexing is possible to multiplex anytype of service, including services with different QoS

parameters


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Traffic volume monitoring

MAC receives RLC PDUs together with statusinformation on the amount of data in the RLCtransmission buffer

MAC compares the amount of data corresponding to atransport channel with the thresholds set by RRC

if the amount of data is too high or too low, MAC sendsa measurement report on traffic volume status to RRC


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RRC can also request MAC to send these measurements

periodically

RRC uses these reports for triggering reconfiguration of

Radio Bearers and/or Transport Channels


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Dynamic Transport Channel type switching

execution of the switching between common and

dedicated transport channels is based on a switching

decision derived by RRC

Ciphering if a radio bearer is using transparent RLC mode, ciphering

is performed in the MAC sub-layer (MAC-d entity)


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Ciphering is a XOR operation (as in GSM and GPRS) wheredata is XORed with a ciphering mask produced by aciphering algorithm

in MAC ciphering, the time-varying input parameter(COUNT-C) for the ciphering algorithm is incremented at

each transmission time interval (TTI), that is, once every 10,20, 40 or 80 ms depending on the transport channelconfiguration

each radio bearer is ciphered separately

the ciphering details are described in 3GPP specification TS

33.102


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Access Service Class (ASC) selection for RACH

transmission

PRACH resources (i.e. access slots and preamble

signatures []for FDD) may be

divided between different Access Service Classes inorder to provide different priorities of RACH usage

the maximum number of ASCs is eight

MAC indicates the ASC associated with a PDU to the

physical layer


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7.3.3 LOGICAL CHANNELS

The data transfer services of the MAC layer are

provided on logical channels

Logical channels are classified into two groups

control channels

used to transfer control plane information

traffic channels

used to transfer user plane information


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Control Channels

Broadcast Control Channel (BCCH)

a downlink channel for broadcasting system control

information

Paging Control Channel (PCCH)

a downlink channel that transfers paging information


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Dedicated Control Channel (DCCH)

a point-to-point bidirectional channel that transmits

dedicated control information between a UE and RNC

this channel is established during RRC connection

establishment procedure


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Common Control Channel (CCCH)

a bidirectional channel for

transmitting control information

between the network and UEs

this logical channel is always

mapped onto RACH/FACHtransport channels

a long UTRAN UE identity is

required (U-RNTI, which includes

SRNC address)

so that the uplink messages can

be routed to the correct servingRNC even if the RNC receiving

the message is not the serving

RNC of this UE


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Traffic Channels Dedicated Traffic Channel (DTCH)

a point-to point channel, dedicated to one UE, for the transferof user information

can exist in both uplink and downlink

Common Traffic Channel (CTCH) a point-to-multipoint downlink channel for transfer of dedicated

user information for all, or a group of specified, UEs

7 3 4 MAPPING BETWEEN LOGICAL


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7.3.4 MAPPING BETWEEN LOGICALCHANNELS AND TRANSPORT

CHANNELS

Figure 7.3 shows the mapping between logical channels

and transport channels

Connections between logical channels and transport

channels

PCCH is connected to PCH [down]

BCCH is connected to BCH [down]and may also be connected

to FACH [down]


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DCCH and DTCH can be connected toRACH [up]and FACH [down]

CPCH [up]and FACH [down]

RACH [up]and DSCH [down]

DCH [up]and DSCH [down]DCH [up] and DCH [down]

CCCH is connected to RACH [down]and FACH [down]

CTCH is connected to FACH [down]


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7.4 THE RADIO LINK CONTROL

PROTOCOL

RLC protocol provides segmentation and

retransmission services for both user and control

data

Each RLC instance is configured by RRC to

operate in one of three modes Transparent mode (Tr)

Unacknowledged Mode (UM)

Acknowledged Mode (AM)


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The service the RLC layer provides

in the control plane

called Signaling Radio Bearer (SRB)

in the user plane

called Radio Bearer (RB)

service provided by PDCP, BMC protocols, or else


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7.4.1 RLC LAYER ARCHITECTURE

Figure 7.5 shows the RLC layer architecture

all three RLC entity types and their connection to RLC-

SAPs and to logical channels (MAC-SAPs) are shown

the transparent and unacknowledged mode RLC entities

are defined to be unidirectional the acknowledged mode entities are described as

bidirectional


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For all RLC modes

CRC (Cyclic Redundancy Check) error detection is

performed on physical layer

the result of CRC check is delivered to RLC, together

with the actual data


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In transparent mode

no protocol overhead is added to higher layer data

erroneous protocol data units (PDUs) can be discarded

or marked erroneous

example transmission can be of the streaming type


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In unacknowledged mode no retransmission protocol is in use and data delivery is

not guaranteed

received erroneous data is either marked or discardeddepending on the configuration

on the sender side, a timer-based discard withoutexplicit signaling function is applied

RLC SDUs which are not transmitted within aspecified time are simply removed from thetransmission buffer


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an RLC entity in unacknowledged mode is defined as

unidirectional

because no association between uplink and downlink

is needed

example of user services using unacknowledged modeRLC

cell broadcast service

Voice over IP (VoIP)


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In acknowledged mode

an automatic repeat request (ARQ) mechanism is used

for error correction

the quality vs. delay performance of RLC can be

controlled by RRC through configuration of the numberof retransmissions provided by RLC

in case RLC is unable to deliver the data correctly (max

number of retransmissions reached or the transmission

time exceeded)

the upper layer is notified and the RLC SDU (ServiceData Unit) is discarded


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RLC can be configured for both in-sequence and out-of-sequence delivery

in-sequence delivery

the order of higher layer PDUs is maintained

out-of-sequence delivery

forwards higher layer PDUs as soon as they arecompletely received

the acknowledged mode is the normal RLC mode forpacket-type services, examples

Internet browsing

email downloading


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7.4.2 RLC FUNCTIONS

Segmentation and reassembly

performs segmentation/reassembly of variable-length

higher layer PDUs into/from smaller RLC Payload Units

(PUs)

one RLC PDU carries one PU the RLC PDU size is set according to the smallest

possible bit rate for the service using RLC entity


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Protocol Data Unit (PDU)

in layered systems, a unit of data that is specified in a

protocol of a given layer and that consists of

protocol-control information of the given layer

possibly user data of that layer


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for variable rate services, several RLC PDUs need to be

transmitted during one transmission time interval when

any bit rate higher than the lowest one is used


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Concatenation if the contents of an RLC SDU do not fill an integral

number of RLC PUs, the first segment of the nextRLC SDU may be put into the RLC PU inconcatenation with the last segment of the previousRLC SDU

SDU1 SDU2

PU1 PU2 PU3 PU4 PU5 PU6


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Padding when concatenation is not applicable and the

remaining data to be transmitted does not fill anentire RLC PDU of given size, the remainder of thedata field is filled with padding bits

Transfer of user data RLC supports acknowledged, unacknowledged and

transparent data transfer

transfer of user data is controlled by QoS setting


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Error correction provides error correction by retransmission in the

acknowledged data transfer mode

In-sequence delivery of higher layer PDUs preserves the order of higher layer PDUs that were

submitted for transfer by RLC using theacknowledged data transfer service

if this function is not used, out-of-sequence deliveryis provided


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Duplicate detection

detects duplicated received RLC PDUs and ensures

that the resultant higher layer PDU is delivered only

once to the upper layer

Flow control allows an RLC receiver to control the rate at which

the peer RLC transmitting entity may send

information


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Sequence number check

guarantees the integrity of reassembled PDUs

provides a means of detecting corrupted RLC SDUs

through checking the sequence number in RLC

PDUs when they are reassembled into an RLC SDU a corrupted RLC SDU is discarded


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Protocol error detection and recovery

detects and recovers from errors in the operation of

RLC protocol

Ciphering

performed in the RLC layer for acknowledged andunacknowledged RLC modes


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the same ciphering algorithm is used as for MAC layerciphering

the only difference being the time-varying inputparameter (COUNT-C) for the algorithm, which forRLC is incremented together with the RLC PDU

numbers for retransmission

the same ciphering COUNT-C is used as for theoriginal transmission; this would not be so if cipheringwere on the MAC layer

ciphering details are described in 3GPP specificationTS 33.102


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Suspend/resume function for data transfer

suspension is needed during the security mode

control procedure so that the same ciphering keys

are always used by the peer entities

suspensions and resumptions are local operationscommanded by RRC via control interface


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7.5 THE PACKET DATA CONVERGENCE

PROTOCOL

PDCP exists only in the user plane andonly for services from PS domain

PDCP contains compression methods

which are needed to get better

spectral efficiency for services

requiring IP packets to betransmitted over the radio

For 3GPP Release 99 standards

a header compression method is

defined, for which several header

compression algorithms can beused


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Example of why header compression is valuable

the size of the combined RTP/UDP/IP headers

at least 40 bytes for IPv4

at least 60 bytes for IPv6

the size of the payload

for example, for IP voice service, can be about 20

bytes or less


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7.5.1 PDCP Layer Architecture

7.5.2 PDCP Functions


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7.5.1 PDCP LAYER ARCHITECTURE

Figure 7.7 shows an example of PDCP layerarchitecture

Multiplexing of Radio Bearers in PDCP layer is

illustrated in Figure 7.7

with two PDCP SAPs (one with dashed lines) providedby one PDCP entity using AM RLC


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Every PDCP entity uses zero, one or severalheader compression algorithm types with a set ofconfigurable parameters

Several PDCP entities may use the same algorithm

types The algorithm types and their parameters

negotiated during RRC Radio Bearer establishment orreconfiguration procedures

indicated to PDCP through PDCP Control Service

Access Point (SAP)


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7.5.2 PDCP FUNCTIONS

Compression of redundant protocol controlinformation (e.g. TCP/IP and RTP/UDP/IP

headers) at the transmitting entity, and

decompression at the receiving entity

the header compression method is specific to theparticular network layer, transport layer or upper layer

protocol combinations, for example TCP/IP and

RTP/UDP/IP

the only compression method mentioned in PDCP

Release99 specification is RFC2507


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Transfer of user data

PDCP receives a PDCP SDU and forwards it to the

appropriate RLC entity and vice versa

Support for lossless SRNS relocation

those PDCP entities which are configured to supportlossless SRNS relocation have PDU sequence

numbers, which, together with unconfirmed PDCP

packets are forwarded to the new SRNC during

relocation

only applicable when PDCP is using acknowledged

mode RLC with in sequence delivery

7 6 THE BROADCAST/MULTICAST


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7.6 THE BROADCAST/MULTICAST

CONTROL PROTOCOL

Broadcast/Multicast Control(BMC) protocol

service-specific Layer 2 protocol

exists only in the user plane

This protocol is designed toadapt broadcast and multicast

services, originating from the

Broadcast domain, on the radio

interface


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In Release99 of the standard, the only serviceutilizing this protocol is SMS Cell Broadcast service

This service is directly taken from GSM

It utilizes UM RLC using CTCH (Common Traffic

Channel) logical channel which is mapped into FACHtransport channel


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7.6.1 BMC Layer Architecture

7.6.2 BMC Functions


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7.6.1 BMC LAYER ARCHITECTURE

The BMC protocol, shown in Figure 7.8, does nothave any special logical architecture


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7.6.2 BMC FUNCTIONS

Storage of Cell Broadcast messages the BMC in RNC stores the Cell Broadcast messages

received over the CBCRNC interface for scheduled

transmission

CBC: Cell Broadcast Centre


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Traffic volume monitoring and radio resourcefor CBS

on the UTRAN side, BMC

calculates the required transmission rate for Cell

Broadcast Service based on the messages

over CBCRNC interface

requests appropriate CTCH/FACH resources

RRC

CTCH: Common Traffic Channel


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Scheduling of BMC messages the BMC receives scheduling information together with

each Cell Broadcast message over the CBCRNCinterface

based on this scheduling information

on the UTRAN side, BMC generates schedule messages

schedules BMC message sequences


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Transmission of BMC messages to UE this function transmits the BMC messages (Scheduling

and Cell Broadcast messages) according to the schedule

Delivery of Cell Broadcast messages to the upper layer

this UE function delivers the received non-corrupted CellBroadcast messages to the upper layer


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Applicability

CBS

has been used for low rate information, like sending cell

location name etc.

MBMS the mostly quoted data rate has been 64 kbps, which

enables more sophisticated content to be distributed


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Depending on the number of users that have joined toreceive the content via the MBMS, the network can

select to use

point-to-point transmission

DCH is used as the transport channel point-to-multipoint transmission

FACH is used as the transport channel in a particular cell

for the MBMS content


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On the physical layer

DCH is mapped to DPDCH (Dedicated Physical Data

channel)

FACH is mapped to SCCPCH (Secondary Common Control

Physical Channel) In the case of point-to-point connection

the logical channel can be DCCH or DTCH with all the

mapping in Release 99 possible


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In the case of point-to-multipoint case, there are two newlogical channels

MBMS point-to-multipoint Control Channel (MCCH), which

carries the related control information

MBMS point-to-multipoint Traffic Channel (MTCH), whichcarries the actual user data


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UTRAN shall decide, based on the number of UEs in aparticular cell

which mode of MBMS operation to use, and if the situationchanges, the network can transfer the UEs between differentstates of MBMS reception (Figure 7.9)


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Figure 7.10 shows an example scenario one cell uses point-to-multipoint while another cell has only

one joined UE which is kept in the point-to-point state


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7 8 THE RADIO RESOURCE CONTROL


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7.8 THE RADIO RESOURCE CONTROL

PROTOCOL

Radio Resource Control (RRC) messages the major part of the control signaling between UE and

UTRAN

carry all parameters required to set up, modify and release

Layer 1 and Layer 2 protocol entities carry in their payload also all higher layer signaling

MM (Mobility Management)

CM (Connection Management)

SM (Session Management)


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The mobility of user equipment in the connected mode iscontrolled by RRC signaling, which are measurements

handovers

cell updates


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7.8.1 RRC Layer Logical Architecture

7.8.2 RRC Service States

7.8.3 RRC Functions

7.8.1 RRC LAYER LOGICAL


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7.8.1 RRC LAYER LOGICAL

ARCHITECTURE

Figure 7.11 shows the RRC layer logical architecture

RRC layer has four functional entities

1. Dedicated Control Function Entity (DCFE)

handles all functions and signaling specific to one UE

in the SRNC there is one DCFE entity for each UEhaving an RRC connection with this RNC


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DCFE uses mostly acknowledged mode RLC (AM-SAP),but some messages are sent using unacknowledged mode

SAP (e.g. RRC Connection Release) or transparent SAP

(e.g. Cell Update)

DCFE can utilize services from all Signaling Radio

Bearers


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2. Paging and Notification control Function Entity (PNFE)

handles paging of idle mode UE(s)

there is at least one PNFE in the RNC for each cell

controlled by this RNC

PNFE uses PCCH logical channel normally viatransparent SAP of RLC

PNFE could utilize also UM-SAP


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In this example architecture the PNFE in RNCwhen receiving a paging message from an Iu interface

needs to check with the DCFE whether or not this UE

already has an RRC connection (signaling connection

with another CN domain)

if it does, the paging message is sent (by the DCFE)

using the existing RRC connection


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3. Broadcast Control Function Entity (BCFE) handles the system information broadcasting

there is at least one BCFE for each cell in the RNC

BCFE uses either BCCH or FACH logical channels,

normally via transparent SAP BFCE could utilize also UM-SAP


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4. Routing Function Entity (RFE) normally drawn outside of the RRC protocol and

logically belonging to the RRC layer, since theinformation required by this entity is part of RRCmessages

its task is the routing of higher layer messages to different MM/CM entities (UE side), or

different core network domains (UTRAN side)


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7.8.2 RRC SERVICE STATES

Two basic operational modes of a UE idle mode

connected mode

Connected mode can be further divided into service

states, which define what kind of physical channels a UEis using


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Figure 7.12 shows the main RRC service states in the connected mode

the transitions between idle mode and connected mode

the possible transitions within the connected mode


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In the idle mode after a UE is switched on, it selects (either automatically or

manually) a PLMN to contact

the UE looks for a suitable cell of the chosen PLMN

chooses that cell to provide available services, and tunes toits control channel

this choosing is known as camping on a cell

after camping on a cell in idle mode

the UE is able to receive system information and cellbroadcast messages


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the UE stays in idle mode until it transmits a request toestablish an RRC connection

in idle mode the UE is identified by identities such as IMSI,

TMSI and P-TMSI (Packet-TMSI)


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In the Cell_DCH state a dedicated physical channel is allocated to the UE

the UE is known by its serving RNC on a cell or active set

level

the UE performs measurements and sends measurementreports according to measurement control information

received from RNC


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In the Cell_FACH state no dedicated physical channel is allocated for the UE, but

RACH and FACH channels are used instead, for transmittingboth signaling messages and small amounts of user plane data

the UE is also capable of listening to the broadcast channel

(BCH) to acquire system information the UE performs cell reselections, and after a reselection

always sends a Cell Update message to the RNC, so that theRNC knows the UE location on a cell level


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for identification, a C-RNTI (Cell-Radio Network TemporaryIdentity) in the MAC PDU header separates UEs from each

other in a cell

when the UE performs cell reselection it uses the U-RNTI

(UTRAN-Radio Network Temporary Identity) when sending

the Cell Update message

so that UTRAN can route the Cell Update message to the

current serving RNC of the UE


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In the Cell_PCH state the UE is still known on a cell level in SRNC, but it can be

reached only via the paging channel (PCH)

in this state the UE battery consumption is less than in the

Cell-FACH state

since the monitoring of the paging channel includes a

discontinuous reception (DRX) functionality

the UE also listens to system information on BCH


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a UE supporting Cell Broadcast Service (CBS) is also capableof receiving BMC (Broadcast/ multicast control protocol)

messages in this state

if the UE performs a cell reselection

it moves autonomously to the Cell-FACH state to execute

the Cell Update procedure

after which it re-enters the Cell-PCH state if no other

activity is triggered during the Cell Update procedure


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The URA_PCH state very similar to the Cell_PCH

except that the UE does not execute Cell Update after eachcell reselection, but instead reads UTRAN Registration Area(URA) identities from the broadcast channel

only if the URA changes does UE inform its location to theSRNC

this is achieved with the URA Update procedure, which issimilar to the Cell Update procedure


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When RRC connection is released or at RRC connectionfailure

the UE leaves the connected mode and returns to idle mode

7.8.2.1 ENHANCED STATE MODEL


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FOR MULTIMODE TERMINALS

Figure 7.13 an overview of the possible state transitions of a multimode

(UTRA FDDGSM/GPRS) terminal

With these terminal types it is possible to perform

inter-system handover between UTRA FDD and GSM inter-system cell reselection from UTRA FDD to GPRS


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7.8.2.2 EXAMPLE STATE TRANSITION


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CASES WITH PACKET DATA

When sending or receiving reasonable amounts of data UE will stay in Cell_DCH state

Once the data runs out and timers have elapsed

UE will be moved away from Cell_DCH state

Moving back to the Cell_DCH state always requires signaling between UE and SRNC

the network sets up the necessary links to Node B


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Use of Cell_DCH or Cell_FACH state is always a trade-off between

terminal power consumption

service delay

signaling load network resource utilization


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Figure 7.14 shows the signaling flow of UE-initiatedRRC state transition

an application has created data to be transmitted to the

network

UE goes to Cell_FACH state sending data on RACH is not sufficient, a DCH needs to be

set up


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once in Cell_FACH state

the UE initiates signaling on the RACH

(1)

after the network has received the

measurement report on RACH (4)and a

radio link has been set up between

Node B and RNC (5)

the reconfiguration message is sent on

FACH to inform of the DCH parameters

to be used (6)


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Figure 7.15 shows the signaling flow of Network-initiated RRC state transition

the network-initiated RRC state change occurs when there is

too much downlink data to be transmitted, and using FACH is

not enough

the network first transmits the paging message in the cell

where the terminal is located (as the terminal location is

known at cell level in Cell_PCH state) (1)


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upon reception of the paging message, the terminal moves toCell_FACH state and initiates signaling on the RACH (2)

now there is no need for any measurement report as transition

is initiated by the network

the response from the terminal in the example case is a

reconfiguration complete message (5), assuming the DCH

parameters have been altered in connection to the state

transition


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7 8 3 RRC FUNCTIONS


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7.8.3 RRC FUNCTIONS

Establishment, maintenance and release of an RRCconnection between UE and UTRAN

Control of Radio Bearers, transport channels and

physical channels

Control of security functions (ciphering and integrityprotection)

Broadcast of system information, related to access

stratum and non-access stratum


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Access stratum the set of protocols and capabilities relevant to radio

technique

Non access stratum

those technique which are independent of radio accessnetwork

capabilities

call and session control (set up, modify and release

the transmission logic resources relevant to the

required service)

mobility control (enable the user to communicate

regardless of his location)


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Paging Initial cell selection and reselection in idle mode

Integrity protection of signaling messages

UE measurement reporting and control of the

reporting

RRC connection mobility functions

Support of SRNS relocation


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Support for downlink outer loop power control in theUE

Open loop power control

Cell broadcast service related functions

Support for UE positioning functions

UMTS_ RLC and MAC Layer in Detail

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