02_MTP

Switching Core Network Signalling Message Transfer Part Training Document M14/U4

© Nokia Siemens Networks

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Contents


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Contents

1 Objectives ...............................................................................................5

2 Introduction ............................................................................................6

3 Signalling Network.................................................................................8 3.1 Addressing Signalling Points....................................................................8

4 MTP layers ............................................................................................10 4.1 MTP Layer 1: Signalling Data Link .........................................................10 4.2 MTP Layer 2: Signalling Link..................................................................10 4.2.1 Signal Units ............................................................................................11 4.2.2 Error Correction......................................................................................15 4.2.3 Signalling Link Failure Detection............................................................16 4.2.4 Level 2 Procedures ................................................................................16 4.3 MTP Layer 3: Signalling Network ...........................................................19 4.3.1 MTP3 Message Structure.......................................................................19 4.3.2 Signalling Message Handling.................................................................23 4.3.3 Signalling Network Management............................................................26 4.3.4 Signalling Traffic Management Procedures ...........................................30 4.3.5 Signalling Route Management Procedures............................................32 4.3.6 Signalling Link Management Procedures...............................................38

5 MTP Alarms ..........................................................................................40

6 MTP Parameters Handling...................................................................42 6.1 Level 3 Parameters ................................................................................43 6.2 CCS7 Signalling Network-Specific Parameters......................................48 6.3 Signalling Link Specific Parameters .......................................................53 6.4 Signalling Route Set Specific Parameters..............................................63

Summary of changes


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Summary of changes

Objectives


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1 Objectives On completion of this module, you should be able to:

• Describe the functionality of MTP layer

• Explain MTP message structure

• Explain the MTP procedures

• Output and interpret analysing results

• List MTP parameter in DX200 NE

Introduction


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2 Introduction The CCS#7 Structure divides the signalling functions into “Message Transfer Parts” and the “User Parts” for different users and applications.

The user part communicates with a corresponding user part in the adjoining network element.

The MTP serves as a common transport system that provides reliable transmission of the signalling messages between the communicating user parts, regardless of the unreliability of the physical transmission media. MTP is covered under ITU-T specifications Q.701 –707. The functions of the MTP are divided into three levels:

• Level 3 Signalling network functions

• Level 2 Signalling link functions

• Level 1 Signalling data link functions

The signalling data link function (level 1) defines the physical, electrical and functional characteristics of a signalling data link and the means to access it. The level 1 function provides a bearer for a signalling link.

The signalling link function (level 2) defines the functions considering message transfer between two adjacent network elements through a signalling link. It defines the message structure, framing, error detection and correction, alignment procedure, and so on.

The signalling network function (level 3) can be divided into two parts: message handling, which includes message routing and distribution to the respective user part, and network management, which provides all the necessary procedures for using the signalling network in an optimal way.

Introduction


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MTP2

MTP3

Layer 4(User Part) ISUP TUP SCCP Other User Parts

Signalling

MTP2

MTP1

Signalling LinkFunction

Signalling Data LinkFunction

Signalling MessageHandling

Signalling NetworkManagement

Control signals Signalling message flow

Figure 1. MTP Layers

Signalling Network


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3 Signalling Network A signalling network comprises of signalling points. A distinction is made between 2 categories:

• Signalling end points (SEP)

• Signalling transfer points (STP)

The signalling end points are the sources (origination points) and destinations (destination points) of the signalling traffic. In communications network both these points are usually switching centers.

On the basis of the destination address, the signalling transfer points forward received signalling messages to another signalling transfer point or, where applicable, to a signalling end point. No processing of the message content takes places in a signalling transfer point. A signalling transfer point may be integrated in a signalling point (e.g. a switching cent) or may be a separate node in the signalling network.

3.1 Addressing Signalling Points

All signalling points are identified by a signalling point code (SPC) which is defined by a corresponding numbering scheme and can therefore be addressed specifically in a signalling message.

The signalling point code is a 14 bit value (ITU-T SS7 standard) and can be allocated into subfield, for example, 3-8-3 bit for international use (see ITU-T Q.708).

Since the signalling point code with 14 bits (0…16383) is insufficient to address all signalling points worldwide, it is always used together with the network indicator. The network indicator has four values: NA0, NA1, IN0, and IN1.

Signalling Network


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SEP

STP

Signalling link

Signalling link

SEP

SEP SEP

Signallingend point

Signallingend point

Signallingend point

Signallingend point

Signalling transfer point

DPC = XSignalling link

DPC = X

Figure 2. Components of a signalling network, SEP and STP

Signalling Point Codes •National use

Length: 14 bits (ITU-T SS7 standard), 16 bits (Japan SS7 standard), or 24 bits (China or ANSI SS7 standard) Format: can be allocated into subfields

•International use (ITU-T Q.708)3bit-8bit-3bit meaning: Zone-Area-Signalling point

Network Indicator•NA0 National network 0•NA1 National network 1•IN0 International network 0•IN1 International network 1

Figure 3. SPC and network indicator

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4 MTP layers 4.1 MTP Layer 1: Signalling Data Link

Signalling data link level (level 1) defines the physical, electrical and functional characteristics and the physical interface (E1 or T1) towards the transmission media.

In digital systems normally 64 kbps or 56 kbps channels are used, that is, a timeslot of PCM30 or PCM24 respectively. The choice of the timeslot may be any timeslot except TS “0”. These are governed by the G.703 and G.704 specifications. This channel is called a link.

Level 1 function is specified in Recommendation Q.702.

4.2 MTP Layer 2: Signalling Link

Signalling link level (level 2) defines the functions and procedures for and relating to the transfer of signalling messages over one individual signalling data link. The level 2 functions, together with a level 1 signalling data link as a bearer, provide a signalling link for reliable transfer of signalling messages between two directly connected signalling points.

Signalling messages delivered by superior hierarchical levels are transferred over the signalling link in variable length signal units. The signal units include transfer control information for proper operation of the signalling link in addition to the signalling information.

The signalling link functions comprise:

1. delimitation of signal unit by means of flags

2. flag imitation prevention by bit stuffing

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3. error detection by means of check bits included in each signal units

4. error correction by retransmission and signal unit sequence control by means of explicit sequence numbers in each signal unit and explicit continuous acknowledgements

5. signalling link failure detection by means of signal unit error rate monitoring and signalling link recovery by means of special procedures

Level 2 functions are specified in Recommendation Q.703.

User Part

Level 1

Flag Detection and Bit-stuffing

Flag Detection and Bit-stuffing

ControllerController

Retransmission Buffer


Message Length Check

Message Length Check

Checksum Generation and

Comparison

Checksum Generation and

Comparison

Sequence Number Check

Sequence Number Check

Received BufferReceived Buffer

Flag Generation and Bit-stuffing

Flag Generation and Bit-stuffing

Checksum Generation

Checksum Generation

Sequence Number Generation

Sequence Number Generation

Transmit BufferTransmit Buffer

Level 1

FSN BSN

BIB

Figure 4. MTP Layer 2 functions

4.2.1 Signal Units

The message transfer part transports messages in signal units of variable length towards destination. A signal unit is formed by the function of level 2. In addition to the message it also contains control information for the message exchange.

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There are three different types of signal units:

1. Message signal units (MSU)

2. Link status signal units (LSSU)

3. Fill-in signal units (FISU)

Types of signal units are differentiated by means of the length indicator contained in all signal units. Message signal units are used for the transport of the user part messages. Link status signal units contain information about state of the signalling link. Fill-in signal units contain no additional information. It is used when there is no message to be sent on the link. Own side has no messages to send, but the remote end expects acknowledgements for the message signal units that it has sent.

Message signal units are retransmitted in case of error; link status signal unit and fill-in signal unit are not. The basic formats of the signal units are shown in Figure 5.

4.2.1.1 Function and Codes of The Signal Unit Fields

Flag (F) The signal units are of varying length. The opening flag indicates the start of a signal unit. The opening flag of one signal unit is normally the closing flag of the preceding signal unit. The bit pattern for the flag is “0111 1110” or 7Eh. The flag is also used for alignment of the signalling link at the far-end.

Bit stuffing for “Flag imitation prevention” is done by inserting a “0” after 5 consecutive “1” in a message data stream. At the receiving end a “0” is deleted after five consecutive ones in the received data stream.

Backward sequence number (BSN) It is the sequence number of a signal unit being acknowledged.

Backward indicator bit (BIB) With this bit, faulty signal units are requested to be retransmitted for error correction.

Forward sequence number (FSN) It is the sequence number of the signal unit in which it is carried. FSN and BSN are numbers in binary code from a cyclic sequence ranging from 0 to 127.

Forward indicator bit (FIB) It indicates whether a signal unit is being sent for the first time or whether it is being retransmitted.

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F CK SIF SIO LIFIB

FSNBIB

BSN F

8 16 8n, n>2 8 2 6 1 7 1 7 8 [bit]

MSU First bittransmitted

length indicator >2 and ≤63

F CK SF LIFIB

FSNBIB

BSN F

8 16 8 or 16 2 6 1 7 1 7 8 [bit]

LSSU First bittransmitted

length indicator = 1 or 2

F CK LIFIB

FSNBIB

BSN F

8 16 2 6 1 7 1 7 8 [bit]

FISU First bittransmitted

length indicator = 0F FlagBSN Backward Sequence NumberBIB Backward Indicator BitFSN Forward Sequence NumberFIB Forward Indicator Bit

LI Length IndicatorSIO Service Information OctetSIF Signalling Information FieldCK Check BitsSF Status Field

Figure 5. Signal unit formats

Length indicator (LI) The length indicator is used to indicate the number of octets following the length indicator octet and preceding the check bits. Length indicator is a number in binary code in the range of 0-63. It differentiates between the three types of signal units as follows:

Length indicator = 0: Fill-in signal unit

Length indicator = 1 or 2: Link status signal unit

Length indicator > 2: Message signal unit

In the case that the signalling information field (SIF) is spanning 62 octets or more, the length indicator is set to 63.

Service information octet (SIO) The service information octet only exists in message signal units. It contains the service indicator and the subservice field.

Signalling information field (SIF) The signalling information field only exists in message signal units. It contains the actual user message.

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Check bits (CK) CRC16 checksum is inserted in each signal unit for error detection. A checksum is calculated for the data between the flags and inserted in the signalling unit. At the remote end the checksum is recalculated, if the calculated and received checksums do not match, a negative acknowledgement is conveyed by setting BSN to the received FSN and inverting the previously transmitted BIB. This BIB will remain in the new state till a new error occurs.

Status field (SF) The status field only exists in link status signal units. It contains status indications of the signalling link. Only three bits are used to represent signal status. The possible state and corresponding messages are stated below. Their coding is shown in Figure 6.

• Status indication “O” (SIO) Link out of alignment

• Status indication “N” (SIN) Normal alignment

• Status indication “E” (SIE) Emergency alignment

• Status indication “OS” (SIOS) Link out of service

• Status indication “PO” (SIPO) Processor outage

• Status indication “B” (SIB) Busy

• Bit 000 Status indication “O” (SIO) Link out of alignment• Bit 001 Status indication “N” (SIN) Normal alignment• Bit 010 Status indication “E” (SIE) Emergency alignment• Bit 011 Status indication “OS” (SIOS) Link out of service• Bit 100 Status indication “PO” (SIPO) Processor outage• Bit 101 Status indication “B” (SIB) Busy

F CK SF LIFIB

FSNBIB

BSN F

8 16 8 or 16 2 6 1 7 1 7 8 [bit]

LSSU First bittransmitted

X 0 0 0X X X X

D C B A

Figure 6. Link status indications in LSSU

,

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4.2.2 Error Correction

Error correction is through retransmission. Two techniques of error correction are provided, the basic method and the preventive cyclic retransmission method. Both error correction techniques apply only to MSU but not to LSSU and FISU.

Basic error correction is implemented by a negative acknowledgement through BIB and retransmission after inverting FIB. All signalling units are repeated from that sequence number. Positively acknowledged signalling units are deleted from the retransmission buffer.


Signalling TerminalSignalling Terminal

MSU

Negative Acknowledgement

Retransmission

Figure 7. Basic error correction method

The preventive cyclic retransmission method is implemented on long distance lines, with transmission time greater than 15ms. Negative acknowledgement is not awaited., instead all unacknowledged and new signalling units are kept in the retransmission buffer and transmitted periodically. The remote end simply waits for the retransmission to correct the error.

Send only positive acknowledgement of

MSU

Retransmission Buffer: Delete a positive

acknowledgement else cyclically transmit buffer

Signalling TerminalSignalling Terminal

Figure 8. Preventive cyclic retransmission method

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4.2.3 Signalling Link Failure Detection

Signalling link failure detection is provided by means of Signal Unit Error Rate Monitoring (SUERM). This is a statistical method of ensuring the permitted error rate on a link. SUERM is a counter, which increments on a detection of error. If 256 signalling units are received error free it decrements by one. This is called the leaky bucket principle. If the SUERM counter reached the pre-set threshold (generally 64), then link is declared faulty and change procedure to a working link takes place. Initial alignment procedure is carried out to recover the faulty link.

+1 for every SU in error

-1 for 256 correctly received SUs

Alarm level

Figure 9. Signal Unit Error Rate Monitoring (SUERM)

4.2.4 Level 2 Procedures

Signalling link recovery is provided by means of special procedures, which are initial alignment procedure, processor outage procedure, and congestion control.

4.2.4.1 Initial Alignment Procedure

The initial alignment procedure is used for link activation and restoration either through MML commands or through SUERM.

5 different states are distinguished:

Link out of service Internally an activate signal changes the link to an idle state.

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Link idle On the idle link an SIO message is sent. On receiving an SIO as acknowledgement the link becomes aligned on both the local and remote end.

Link aligned SIO continues to be exchanged. At this point any one side may decide to send either SIN or SIE and results in proving state. SIE is generally sent. If the entire linkset is out of service, an SIE is sent to recover each link one by one.

Link proving SIN or SIE is sent in response to received SIN or SIE. This initiates either of the two types of proving:

• Normal proving

When SIN was the LSSU, 216 octets are exchanged via the signalling link within 8.2 sec. allowing only 4 signal units to be faulty.

• Emergency proving

If SIE was the LSSU exchanged, 212 octets are exchanged via the signalling link within a time of 0.5 sec with only one SU allowed to be faulty.

In either of the two proving procedures Alignment Error Rate Monitoring (AERM) is used. The AERM counter is set to zero to mark the beginning of an alignment period. Every SU in fault increments the counter by one. If threshold (four or one) is reached before the exchange of pre-requisite octets, start a new alignment period. If five periods fail, the link is marked faulty.

In service After successful execution of the proving period the link becomes active.

A signalling link test message (MSU) is sent on the link, containing the DPC, OPC, SLC, and a test pattern. It is acknowledged from the other side by Signalling Link Test Acknowledgement message (SLTA) with the same bit-pattern. If the test pattern is received correctly, the Link State is marked as available executing and the link can be used for signalling.

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Activate linkSIO

SIO

SIN/SIE

SIN/SIE

FISU

FISU

FISU

FISU

MSU (SLTM)

MSU (SLTA)

Link Idle

Link out of service

Link Aligned

Link Proving

Link In Service

Figure 10. Initial alignment procedure

Out of service Idle

Aligned

In service

Proving

SIOLink activation

SIN/SIE

Figure 11. Process flow between different states

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4.2.4.2 Processor Outage

A processor outage may occur if:

• Signalling messages cannot be transferred to functional level 3 and / or 4 at either network elements

• Else if the state of the link was changed through MML to “Blocked”.

In either of the cases, an LSSU (SIPO) is transmitted and received MSUs are discarded. FISU are exchanged continuously.

4.2.4.3 Congestion Control

In case there is congestion on the receiving side of the signalling connection, an LSSU (SIB) is sent every 200msec, until congestion ceases. MSU and FISU continue to be transmitted as usual. The BSN and BIB values do not change, but show the last acknowledged MSU.

If congestion persists beyond 10 seconds, the link is declared faulty and an LSSU (SIOS) is sent.

4.3 MTP Layer 3: Signalling Network

The signalling network functions (MTP3) can be divided into two parts, namely:

• Signaling message handling, and

• Signaling network management

The purpose of the signaling message handling functions is to ensure that the signaling messages originated by a particular user part at a signaling point (originating point) are delivered to the same user part at the destination point indicated by the sending user part.

The signalling message handling functions are based on the label contained in the messages which explicitly identifies the destination and originating points. The label part used for signalling message handling by the message transfer part is called routing label.

4.3.1 MTP3 Message Structure

The MTP3 message structure is shown on the Figure 12. Basically it consists of 3 main parts: the service information octet (SIO), routing label and user information field.

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The destination of a signal unit is specified in a routing label. The routing label is a component of every user message and is transported in the signalling information filed (SIF). The routing label consists of destination point code (DPC), originating point code (OPC), and signalling link selection (SLS) field.

The service information octet (SIO) contains additional address information. Using the service indicator (SI), the destination message transfer part identifies the user part for which message is intended. The subservice field (SSF) contains the network indicator which enables a message to be identified, for example, as being for national or international traffic.

Link status signal units (LSSU) and fill-in signal units require no routing label as they are only exchanged between level2 of adjacent message transfer parts.

[bit]

SLS OPC DPC

User Information Routing Label SIO

SubserviceField (SSF)

ServiceIndicator (SI)

Signalling Information Field (SIF)

4 14 14 4 4

First bittransmitted

OPC Originating Point CodeDPC Destination Point CodeSLS Signalling Link Selection

0000 (0H): SNM0001 (1H): SNT0011 (3H): SCCP0100 (4H): TUP0101 (5H): ISUP1101 (DH): BICC

00XX (0H) : IN001XX (4H) : IN110XX (8H) : NA011XX (CH) : NA1

Figure 12. MTP3 message structure and coding

The command group NP – SERVICE INFORMATION DATA HANDLING is used to create, modify, delete, and interrogate the signalling service information data of own signalling point.

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Execution of ZNPI command gives the following printout:

Execution printout

Abbreviations used in execution printout

Figure 13. NPI – Interrogate services

Explanation of SIO parameters Signalling network NA0 national network 0

NA1 national network 1

IN0 international network 0

IN1 international network 1

Service indicator index — a hexadecimal 0 - F

The service indicator index indicates the user part within the signalling network.

Service indicator name 1 - 5 ASCII characters

Service existing for STP messages

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The parameter may receive the following values:

Y it is desired that service exists for STP messages

N service does not exist for STP messages

Service existing for user part of own signalling point The parameter may receive the following values:

Y it is desired that service exists for the user part of own signalling point

N service does not exist for the user part of own signalling point

Primary process family — a hexadecimal 1 - FFFF

The number of the primary process family, which handles incoming signalling messages of the user part of one's own signalling point. The parameter is obligatory if service is created for the incoming signalling messages of the user part of one's own signalling point but the parameter cannot be given if no service is created for incoming signalling messages of the user part of one's own signalling point.

Secondary process family — a hexadecimal 1 - FFFF

The number of the secondary process family which handles the incoming signalling messages of the user part of one's own signalling point. The parameter is not obligatory, and it cannot be given if no service is created for the incoming signalling messages of the user part of one's own signalling point

ADDITIONAL INFORMATION One of the services at the minimum

• service for STP messages

• service for the user part in own signalling point

must be created.

If no service is created for incoming messages in one's own signalling point, the parameters PRIMARY PROCESS FAMILY and SECONDARY PROCESS FAMILY cannot be given.

If service is created for incoming messages in the user part of own signalling point, the parameter PRIMARY PROCESS FAMILY must be given.

If SERVICE INDICATOR INDEX = 0 and service is created for incoming messages in the user part of one's own signalling point, the default of PRIMARY PROCESS FAMILY is the process family indicator of

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CCNETM and the default of SECONDARY PROCESS FAMILY is the process family indicator of CCDESM.

If SERVICE INDICATOR INDEX = 1 and service is created for incoming messages in the user part of one's own signalling point, the default of PRIMARY PROCESS FAMILY is the process family indicator of CCNETM. PRIMARY PROCESS FAMILY and SECONDARY PROCESS FAMILY cannot have the same value (family process indicator).

4.3.2 Signalling Message Handling

Signalling message handling is responsible for the routing of messages to the appropriate link, and distribution of the received messages within own exchange. This can be divided into three sub functions:

• Message discrimination

• Message distribution

• Message Routing

These functions and interactions between them are shown below.

Message discrimination

Message distribution

Message routing

DPC = own SPC

MTP2

MTP3

User Part

DPC ≠ own SPC

ISUP TUP SCCP Network Management

Signalling message handling

Figure 14. Block diagram of signalling message handling function

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The discrimination function evaluates the destination point code (DPC) of the MSU. If the DPC of the received message is equal to own SPC the message is sent to the distribution function. Otherwise it is sent to the routing function.

The distribution function checks the service information octet (SIO) to find out the suitable user part.

The routing function finds the suitable signalling link for sending the signal unit to another network element. The routing is based on DPC, SIO, and the SLS carried in the message. The SLS in turn defines load sharing, and thus link selection.

4.3.2.1 Load sharing within a Link Set

Load sharing within a link set is based on use of SLS bits (4 bits after OPC in routing label). For example in ISUP messages SLS bits are copied from 4 least significant bits of CIC (circuit identification code). All 4 bits of SLS are used for load sharing regardless of link set size. Load sharing is performed between all available signalling links in a link set.

Link priority has no meaning. In case of a link failure, traffic of the link set is evenly distributed among all remaining available links. The following table describes the relation between SLS-bits and links.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 - - - - - - - - - -- -- -- -- -- -- --

0000 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0001 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 0010 1 1 3 3 3 3 3 3 3 3 3 3 3 3 3 3 0011 1 2 1 4 4 4 4 4 4 4 4 4 4 4 4 4 0100 1 1 2 1 5 5 5 5 5 5 5 5 5 5 5 5 0101 1 2 3 2 1 6 6 6 6 6 6 6 6 6 6 6 0110 1 1 1 3 2 1 7 7 7 7 7 7 7 7 7 7 0111 1 2 2 4 3 2 1 8 8 8 8 8 8 8 8 8 1000 1 1 3 1 4 3 2 1 9 9 9 9 9 9 9 9 1001 1 2 1 2 5 4 3 2 1 10 10 10 10 10 10 10 1010 1 1 2 3 1 5 4 3 2 1 11 11 11 11 11 11 1011 1 2 3 4 2 6 5 4 3 2 1 12 12 12 12 12 1100 1 1 1 1 3 1 6 5 4 3 2 1 13 13 13 13 1101 1 2 2 2 4 2 7 6 5 4 3 2 1 14 14 14 1110 1 1 3 3 5 3 1 7 6 5 4 3 2 1 15 15 1111 1 2 1 4 1 4 2 8 7 6 5 4 3 2 1 16

SLS

LINK

Figure 15. Load sharing within a link set

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4.3.2.2 Load Sharing between Link Sets in a Route Set

For link sets in a route set the value 7 indicates the highest priority route and 0 the lowest priority route.

Load sharing between link sets is independent from load sharing within a link set. Link set size has no effect on the load sharing between link sets. So link set sizes should be equal if load sharing is used. In the DX 200 implementation, 8 link sets can belong to a route set (8 routes). Route priorities are significant because traffic is shared on the routes with same priority. If only one route has highest priority (usually the direct route), no load sharing occurs. Priority is also used in forced rerouting to determine the alternative route. Load sharing between link sets also uses all 4 bits of a SLS. If route priorities are the same and load sharing is allowed load sharing is as follows:

1 2 3 4 5 6 7 8 - - - - - - - - 0000 1 1 1 1 1 1 1 1 0001 1 1 1 1 1 1 1 1 0010 1 1 1 1 1 1 1 2 0011 1 1 1 1 1 2 2 2 0100 1 1 1 2 2 2 2 3 0101 1 1 1 2 2 2 2 3 0110 1 1 2 2 2 3 3 4 0111 1 1 2 2 3 3 3 4 1000 1 2 2 3 3 3 4 5 1001 1 2 2 3 3 4 4 5 1010 1 2 2 3 4 4 5 6 1011 1 2 3 3 4 4 5 6 1100 1 2 3 4 4 5 6 7 1101 1 2 3 4 5 5 6 7 1110 1 2 3 4 5 6 7 8 1111 1 2 3 4 5 6 7 8

LINK SET

SLS

Figure 16. Load sharing between link sets

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4.3.3 Signalling Network Management

The signalling network management functions provide the actions and procedures required to maintain signalling service, and to restore normal signalling conditions in the event of disruption in the signalling network, either in signalling links or at signalling points. The disruption may be in the form of complete loss of a signalling link or a signalling point, or in reduced accessibility due to congestion.

There are 2 categories of signalling network management messages as indicated in the service information octet in MSU:

1. Signalling network management (SNM)

2. Signalling network testing and maintenance (SNT)

Signalling network management (SNM) messages The SNM messages contain a heading code, after the label. It comprises of two parts H0 and H1, 4 bits each, which identify the message. The message structure is shown on the Figure 17.

F CK SIF SIO LIFIB

FSNBIB

BSN F

4 4 4 14 14 4 4 [bit]

MSU First bittransmitted

User Information H1 H0 SLS OPC DPC SSF SI0000

SSF Subservice FieldH0 Heading code indicating which message group the message belong toH1 Heading code indicating the message within the group in question

Figure 17. SNM message structure and coding

The SNM messages are coded as 0000 in the Service indicator subfield in SIO. H0 and H1 indicate the type of message being sent. Figure 18 illustrates the heading code allocation of SNM messages.

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CNPCNSCSSDLC1000DLM

H1

UPU1010UFC

TRA0111TRM

LRTLLTLFULIDLUALIALUNLIN0110MIM

RSRRST0101RSM

TFATFRTFP0100TFM

TFCRCT0011FCM

ECAECO0010ECM

CBACBDCOACOO0001CHM

0000

10000111011001010100001100100001

H0GROUP

Figure 18. Heading code allocation of SNM messages

The SNM messages are listed in Table 1 and 2.

Signalling network testing and maintenance (SNT) messages There are only two SNT messages:

SLTM Signalling Link Test Message

SLTA Signalling Link test Acknowledgement

The additional information carried by these two messages is a test pattern. The SNT messages are coded as 0001 in the Service indicator subfield in SIO

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Table 1. SNM messages related to signalling traffic management

Group H0 Group H1 PDU

ECM ECA Emergency changeover acknowledgement

ECM ECO Emergency changeover order

CHM COA Changeover acknowledgement

CHM COO Changeover order

CHM CBD Changeback declaration

CHM CBA Changeback acknowledgement

MIM LFU Link force uninhibit

MIM LIN Link inhibit

MIM LUN Link uninhibit

MIM LIA Link inhibited acknowledgement

MIM LUA Link uninhibited acknowledgement

MIM LID Link inhibit denied

MIM LLT Link local inhibit test

MIM LRT Link remote inhibit test

TRM TRA Traffic restart allowed

UFC UPU User part unavailable

Table 2. SNM messages related to signalling route management

Group H0 Group H1 PDU

RSM RST Signalling Route Set Test for prohibited destination

RSM RSR Signalling Route Set Test for restricted destination

FCM RCT Signalling Route Set Congestion Test

TFM TFA Transfer allowed

TFM TFC Transfer controlled

TFM TFP Transfer prohibited

TFM TFR Transfer restricted

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The signalling network management is divided into 3 functions:

1. Signalling traffic management function

The signalling traffic management is responsible for the availability of a signalling link or a signalling route by using the following procedures:

− changeover

− changeback

− forced rerouting

− controlled rerouting

− MTP restart

− management inhibiting

− signalling traffic flow control

2. Signalling link management function

The signalling link management function controls the signalling links and is responsible for the state changes by using the following procedures:

− signalling link activation

− signalling link restoration

− signalling link deactivation

− signalling link set activation

3. Signalling route management function

The signalling route management is responsible for the availability of a destination by using the following procedures:

− transfer-prohibited procedure, indicating the unavailability of a destination

− transfer-allowed procedure, indicating the availability of a destination

− transfer-controlled procedure, indicating the overload situation of a destination

− signalling-route-set-test procedure, testing the state of a signalling route set.

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4.3.4 Signalling Traffic Management Procedures

4.3.4.1 Changeover Procedure

In case of a signalling link failure the traffic from failed link is diverted to all other remaining links in a link set, avoiding at the same time loss of messages, duplication or wrong order. When a signalling link fails the load sharing table is calculated again.

Changeover order signal (COO) is sent to the remote end via one of available signalling links inside the signalling link set. It indicates the SLC of the faulty link.

The new link may be on the same link set or on an alternate route.

Procedure:

• When a signalling link is detected as faulty (state change to SIOS) load sharing table of signalling LINKSET is recalculated.

• The signalling traffic on the faulty link is stopped; new signalling messages for this link are buffered in the delay buffers of alternative signalling links x, y...

• A changeover message (COO) is sent to the remote end. This changeover message contains the Signalling Link Code (SLC) of the faulty link and the sequence number of the last successfully RECEIVED (not transmitted) SU.

• The remote end proceeds in the same way.

• The reception of a changeover message is acknowledged by sending a changeover acknowledge message (COA).

• Related to the FSN included in the received changeover message the messages, which did not arrive at the remote end, will be sent via the alternative link (= retrieval procedure).

• After the retrieval the contents of delay buffers are released and the traffic continues normally on all remaining available links.

4.3.4.2 Changeback Procedure

The objective of the changeback procedure is to ensure that the transfer of the signalling from the alternative signalling links to a signalling link that has become available again is successful, while avoiding at the same time loss, duplication or miss sequencing of messages.

Procedure:

• Automatically the traffic is returned to the now available signalling link.

• The signalling link selection table is updated and the new information is distributed to all CCSUs.

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• A changeback message (CBD) is sent to the remote end and acknowledged with a (CBA) message.

A BSLC = X

SLC = Y

1) On link Y, COO (SLC = X, BSN = FSN of last correct received MSU)

2) COA (BSN = FSN of last correctly received MSU)

0) Faulty link

3) Change Signalling Link Selection (SLS) table in CCSU

Figure 19. Change over to a parallel link

A BSLC = X

SLC = Y

3) CBD

4) CBA

0) Recovered link

2) Update signalling link selection table in all CCSUs

1) Traffic to signalling link with SLC = X

Figure 20. Changeback to a recovered link

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4.3.4.3 Emergency Changeover Procedure

An emergency changeover takes place when the signalling terminal becomes faulty. It is not possible to obtain the last FSN of the last correctly received SU.

Procedure:

• The signalling point initiates an emergency changeover through ECO message. (It does not contain any sequence number).

• The remote end, if it has the FSN of the last received message, it may acknowledge through COA, else through ECA.

• In cases of receiving either ECO or ECA, the retransmission buffer is not updated. Instead only new messages are transmitted. Hence some messages may be lost.

4.3.5 Signalling Route Management Procedures

4.3.5.1 Transfer-Prohibited Procedure

The transfer-prohibited procedure is performed at a signalling point acting as a signalling transfer point (STP) for messages relating to a given destination, when it has to notify one or more adjacent signalling points that they must no longer route the concerned messages via that signalling transfer point.

The transfer-prohibited procedure makes use of the transfer-prohibited (TFP) message which contains routing label, transfer-prohibited signal and destination for which traffic transfer is no longer possible.

TFP messages are always addressed to an adjacent signalling point.

Procedure followed on loss of a destination:

• In case of unavailability of a signalling route set (e.g. the route between B and D is not longer available and neither B nor D have any alternative route to reach the destination), B and D send a Transfer Prohibited message including the DPC of the network element, which is no longer reachable to the adjacent signalling points.

• B sends the DPC of D.

• D sends the DPC of B.

• The reception of a transfer prohibited message (TFP) causes a Forced Rerouting.

Additional remark:

The transfer prohibited message is not sent to the BSC.

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2) TFP (DPC=D)

2) TFP (DPC=D) 2) TFP (DPC=B)

1)

SP A

SP B

SP C

SP E

SP D

Figure 21. Transfer-prohibited procedure

4.3.5.2 Forced Rerouting Procedure

On reception of a transfer prohibited message the forced rerouting procedure is activated.

Procedure:

• Alternative route to the destination, which was named in the received TFP, is searched and the traffic is re-routed via the new route.

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1) TFP (DPC=D)

1) TFP (DPC=D)

1)

SP A

SP B

SP C

SP E

SP D

1) TFP (DPC=B)

2) FRR: Signalling traffic to D via C

2) FRR: Signalling traffic to D via E

2) FRR: Signalling trafficto B via C

Figure 22. Forced rerouting procedure

4.3.5.3 Signalling-Route-Set-Test procedure

The signalling-route-set-test procedure is used at a signalling point to test whether or not signalling traffic towards a certain destination may be routed via an adjacent signalling transfer point.

The procedure makes use of the signalling-route-set-test message, and the transfer-allowed and the transfer-prohibited procedures.

The signalling-route-set-test message contains:

• The label, indicating the destination and originating points

• The signalling-route-set-test signal

• The destination, the accessibility of which to be tested

• The current route status of the destination being tested

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Procedure to check availability of the route:

• On reception of a TFP message initiates the signalling route set procedure.

• C and E periodically send an RST message to B and D respectively. This message contains the same DPC as the received TFP message.

• A and C send RST to B with DPC of D.

• E sends RST to D with DPC of B.

• The reception of a RST message causes B respectively D to check the availability of the route.

• In case the signalling point of the message is still unavailable there is no reply.

• In case the signalling point of the message is available again, a Transfer Allowed message is sent back.

RST (DPC=D)

RST (DPC=D) RST (DPC=B)

1)

SP A

SP B

SP C

SP E

SP D

Figure 23. Signalling-route-set-test procedure

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4.3.5.4 Transfer-Allowed Procedure

The transfer-allowed procedure is performed at a signalling point, acting as signalling transfer point for messages relating to a given destination, when it has to notify one or more adjacent signalling points that they may start to route to it.

The transfer-allowed procedure makes use of the transfer-allowed message which contains:

• The label, indicating the destination and originating points

• The transfer-allowed signal

• The destination for which transfer is now possible

Transfer-allowed messages are always addressed to an adjacent signalling point.

Procedure:

• If the route set becomes available again, B and D send a transfer allowed message with the DPC of the network element, which is available again to the adjacent signalling points.

• B sends the DPC of D

• D sends the DPC of B

The reception of a TFA message may cause in a controlled rerouting

2) TFA (DPC=D)

2) TFA (DPC=D) 2) TFA (DPC=B)

1)

SP A

SP B

SP C

SP E

SP D

Figure 24. Transfer-allowed procedure

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4.3.5.5 Controlled Rerouting Procedure

The controlled rerouting procedure may be performed when a previous unavailable route becomes available again.

It has to be distinguished between 3 different cases:

• In the case the route that becomes available again has a higher priority than the route actually used, the controlled rerouting procedure is performed.

• In the case the route that becomes available again has the same priority as the route actually used and load sharing is allowed, the traffic is spread over both routes.

• In the case the route that becomes available again has the same priority as the route actually used and load sharing is denied, the traffic is still sent over the actually used route.

4.3.5.6 Congestion on Link

If even one link is congested on a route, a link is said to be congested. A transfer-controlled procedure is initiated by passing a transfer-controlled (TFC) message to the final destinations. This message may start from an OPC or from a STP. It is sent in every 8th message to the DPC. The TFC message results in informing level four to slow down the signalling messages to the mentioned destination.

4.3.5.7 User Part Availability Control

If the message transfer part is unable to distribute a received message to a local user because that user is unavailable, the message transfer part sends a user part unavailable (UPU) message to the message transfer part at the originating signalling point.

When the originating signalling point’s MTP receives a UPU message, it send an indication to the local user designated in the message. The user should then take appropriate action in order to stop generation of normal signalling information for the unavailable user part.

The UPU message contains

• The label, indicating the destination and originating point

• The user part unavailable signal

• The identity of the unavailable user part

• The cause of the unavailability

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A B1) MSU (DPC = B)

3) UPU

2) Unable to deliver message, subsystem faulty

UPU User part unavailable message

Unavailabilitycause

User partId

2

00 Destination H10001

H00100 Routing Label

14 4 4 324 4

Figure 25. User part availability control

4.3.6 Signalling Link Management Procedures

The possible states defined for a link are available, unavailable, and inhibited. If the link state is either available of inhibited, MTP level 3 traffic continues to pass. The state of a link may change due to:

• Link errors

• Processor outage

• Transmission failure

• Operational activity

The signalling link management takes care of:

• Link management

• Processor outage

• Administrative inhibit procedure

• Signalling link test procedure

4.3.6.1 Link Management Signalling link management is required for:

• Link activation, by using the initial alignment procedure

• Link restoration, by using the same initial alignment procedure, but initiated by the system

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• Link deactivation

• Emergency restart, an initial alignment for links of linkset that has no link available

4.3.6.2 Processor Outage

On failure of the signalling terminal processor:

• A SIPO LSSU is transmitted to the remote end

• This initiates a link changeover procedure

• If the processor fault is removed, a changeback procedure is initiated

• The traffic may then be rerouting through this link

4.3.6.3 Administrative Inhibit Procedure

This is done to administratively block a link and not allow it to come up, so as to make some changes, without loss of signalling. The steps involved are:

• Checks database to find out if a destination may become unavailable as a result

• An LSSU (LIN) message is sent to the remote end. The remote end has a choice to reject the process.

• The remote end sends an LSSU (LIA) as an acknowledgement to inhibit the link. If LIA is not received within a time limit, LIN may be resent. If still no answer is received the process may be aborted.

• The database is updated with link state as inhibited.

To uninhibit the link: The signalling point that inhibited it may uninhibit by LUN message. A remote destination point may force uninhibit by sending an LFU message. If the link has not been inhibited through the remote signalling point, it may recover the link by performing a changeback procedure.

4.3.6.4 Signalling Link Test Procedure

The link testing procedure may be carried out to

• Activate or restore a signalling link

• Continuously, with a period of 30 seconds.

The procedure is initiated by one end sending an LSSU (SLTM) message with a test pattern. The test is said to be successful if, an LSSU (SLTA) is received within 10 seconds and has the same test pattern. If two consecutive tests fail, the link is declared faulty.

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5 MTP Alarms There are some DX 200 alarms related to the MTP level signalling network management: 1038 UPU message received The exchange has received a User Part Unavailable message (UPU). This message informs the sending end of a signalling message that the user part of the destination address is not available. Depending on the unavailable user part (TUP and ISUP) the telephone traffic and signalling traffic fail. In the case of SCCP, used services fail. 1072 Signalling link out of service A signalling link has failed and changed state from IN SERVICE to OUT OF SERVICE, or its initial alignment attempt has failed. If this signalling link is the only one in the signalling link set, the system sets also alarm 2070, LINK SET UNAVAILABLE. If there is an alternative signalling link available in the link set, the system performs a changeover. In this case the signal transmission capacity is also decreased. 1548 MTP confusion message received An MTP confusion message has been received in the exchange. The signalling point indicated by the originating point code given in the 3rd supplementary information field has not identified the signalling network management message. The heading code of the signalling network management message is given in the 6th supplementary information field. 2064 Route set unavailable The signalling point cannot be reached because none of the signalling routes of the signalling route set can be used. Signalling traffic to the signalling point concerned is totally blocked. This might cause a situation where CCS calls to the signalling point concerned fail or where, in the

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worst case, all outgoing calls, for example, fail (the signalling point that cannot be reached is HLR) or all calls of a certain type fail (the signalling point that cannot be reached is for example SCP or SMSC). 2069 Signalling link test failed The signalling link test has failed. Lockout of the signalling link on level 2 has succeeded, but testing the signalling link on level 3 has failed and the signalling link is not brought into use. The system restarts the signalling link and the signalling link test is repeated. 2070 Link set unavailable All signalling links in the signalling link set are unavailable. There is no direct connection to the partner exchange to which this link set is connected. If there is an alternative connection between the exchanges, traffic is routed to that connection. If the alarm 2064 ROUTE SET UNAVAILABLE is also on, there is no connection to the partner exchange or another exchange reached through this signalling link set. There is something wrong with the data transmission connections of the links of this link set, and/or links have been blocked. The exchange automatically attempts to re-establish the connection by attempting to restart the links that are in state UA-INS. The alarm 1072 SIGNALLING LINK OUT OF SERVICE is given for each link that is in state UA-INS. 2072 Failure in signalling link activation or restoration The activation or restoration of a signalling link fails. If there are other available signalling links in the signalling link set, signalling traffic is transmitted through them. Signalling transmission capacity is, however, decreased. The alarm 1072 SIGNALLING LINK OUT OF SERVICE has also been issued about this signalling link.

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6 MTP Parameters Handling It is possible to change the functions of signalling network elements by using various parameters. The parameters can be divided into the following groups:

• MTP

− Level 3 parameters

− CCS7 signalling network specific parameters

− Signalling route set specific parameters

− Signalling link specific parameters

Table 3 shows parameter sets, the effected parts, and MML commands.

Table 3. Parameter sets

Parameter set Effected parts MML commands

MTP level 3 parameters Message Transfer Part of the signalling system

NMI

Signalling network parameters

Whole signalling network NMO

Signalling link parameter sets

Signalling links NOI

Signalling route set parameter sets

Signalling routes NNI

You can modify the functions of the MTP in the Common Channel Signalling (CCS) system to a certain extent by modifying the related parameter values. The parameter values are stored in the parameter files, as listed in Table 4.



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Table 4. Parameter values

Name of parameter file Content

L3PARA Level 3 parameters

RSPARA Signalling route set parameters

SLNPAR Signalling link parameters

SNWPAR Signalling network parameters

6.1 Level 3 Parameters

The level 3 parameters define the functions of the whole MTP. Some of the parameter values are related to monitoring the functions, while others define various limits. In addition, a parameter can have different values depending on the system and release level.

You can handle the level 3 parameters by using the commands NMI and NMM. The command NMI displays the used parameter values grouped by the parameter sets. The command NMM is used to modify the used parameters.

The first parameter in the command defines the parameter set (A-F):

• A - CSS7 general parameters

• B – overload control parameters

• C - timing parameters of own signalling point

• D - parameters for testing/SIO parameters

• E – internal routing parameters

• F - parameters for CSS7 statistics

With the second parameter in the command we define which parameter we want to modify and give the new value, lists the parameter groups, parameters and their indexes, parameter names and their meanings, the possible values of each parameter and the value range, as well as the recommended value, if that exists.



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Table 5. Layer 3 parameters

Parameter Parameter name/meaning

Value

A CSS7 COMMON PARAMETERS

A0-A9 DISTRIB_MTP_UNIT_TYPE_0 - 9 Defines those unit types on an exchange where you can create signalling links. Note: Usually, the parameter values need not be changed in the MSC, HLR, BSC or fixed network exchanges, because unit types CCSU, BCSU and BSU have been installed.

B OVERLOAD CONTROL PARAMETERS

B0 MAX_NB_OF_NOTICES The largest amount of incoming messages allowed to enter a centralised unit during a message-monitoring period (100 ms). Purpose of the parameter is to control overload within the exchange. The parameter value should not be changed.

10...30

C TIMER PARAMETERS FOR OWN SIGNALLING POINT

C0 LINK_TEST_PERIOD 1500...45000 (10 ms)

The sending period for signalling link test messages. The period applies to a group of 10signalling links. This means that when an exchange has 30 links, the test message goes to each link in every third sending period.

4000 (40 sec.)

C1 Q704_T18_LINK_AVAIL_WAIT

1000... 6000 (10 ms)

The time used controlling the availability of the links when a signalling transfer point is restarted. The value depends on the implementation and on the network.

2000

C2 Q704_T19_TRA_WAIT 200... 1000 (10 ms)



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Value

The timer controlling the reception of all TRA messages while the signalling transfer point is being restarted, when the restarting is made as defined in the CCITT Blue Book. The timer is defined by parameter P7 when the system follows the White Book.

400

C3 Q704_T20_TRAF_RESTARTING_TIME

200... 1000 (10 ms)

The timer controlling the sending of all TRA messages when the signalling transfer point is being restarted.

400

C4 T111_T26 1000... 2000 (10 ms)

Defines the timer for resending of TRW messages when the signalling transfer point is being restarted, the timer is defined in the ANSI standards.

1500

C5 Q714_T_GUARD 600... 9600 (100 ms)

Defines the monitoring time used for the signalling connections when the signalling transfer point is being restarted.

6000

C6 T111_T27 300... 500 (10 ms)

After commencing the restart procedure of a signalling point, all the signalling links of the exchange keep sending the processor outage state indicator to the partner exchanges for a given time (defined in this parameter). This is to make sure that all adjacent signalling points recognise that this point cannot be reached any more.

D PARAMETERS FOR TESTING

D0 L2_TEST_MSG_SIO 0 ... FF

The service information octet used by the CCS System Test Message Generator (MSGGEN) reads the data only when it starts up. After changing the parameter values, the MSGGEN has to be restarted before new values can be included in the contents of the test messages.

8F (NA0 network user part F)



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Value

D1 TEST_MSG_LENGTH 0...272

The length of the SIF part in the MSGGEN messages of the CCS System Test Message Generator. This parameter effects only those messages whose length can be modified. Value for this parameter can be changed while the MSGGEN is running, and the MSGGEN needs not be restarted.

smaller than 272

E INTERNAL ROUTING PARAMETERS

E0 INT_ST7_ROUTE ´

Defines the number of the internal routes that include the PCM time slots used by the signalling link terminals between the unit and the switching network.

E1 EXT_ST7_ROUTE

Defines the number of the external routes that include the external PCM timeslots used by the signalling link terminals.

E2 INT_ST7_ROUTE_NAME

Defines the name of the internal route that includes the PCM timeslots used by the signalling link terminals between the unit and the switching network.

E3 EXT_ST7_ROUTE_NAME

Defines the name of the external route that includes the external PCM timeslots used by the signalling link terminals.

E4 INTERNAL_ROUTING_FOR_SL

Defines whether the system tries to update the signalling link related PCM/TSL data into the



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Value

routing data of the CM3PRO. Used only on test exchanges that have no group switch (GSW).

F CSS7 STATISTICS PARAMETERS

F0 SUCC_UNIT_COLL_COUNT_5

2... 10

Defines the number of MTP decentralised units from which the statistics counters are collected during a 5-minute monitoring period.

4

F1 SUCC_UNIT_COLL_COUNT_30

2... 20

Defines the number of MTP decentralised units from which the statistics counters are collected one by one during a 30-minute monitoring period.

10

F2 SL_LOG_TYPE CYCLIC

Type of signalling link event log, which can be either NORMAL or CYCLIC. When the event log is stored in the normal buffer, the buffer can be emptied with command OLE.

CYCLIC

F3 SP_LOG_TYPE CYCLIC

Type of the signalling point event log, which can be either NORMAL or CYCLIC. When the event log is stored in the normal buffer, the buffer can be emptied with command ONE.

CYCLIC

F4 SL_LOG_MAX_COUNT 16... 32

The maximum amount of changes in the state of a signalling link that can be stored in the buffer.

16

F5 SP_LOG_MAX_COUNT 16... 32

The maximum amount of changes in the state of a

16



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Value

signalling point that can be stored in the buffer.

F6 USER_NOTICE_ACT ACTIVE, PASSIVE

Controls the notices for the users statistics output.

F7 SCCP_LOG_TYPE CYCLIC

Type of the SCCP event log buffer. ZOTE to clear the buffer.

F8 TC_LOG_TYPE CYCLIC

Type of the TC event log buffer. ZOTE to clear the buffer

6.2 CCS7 Signalling Network-Specific Parameters

These parameters apply to the whole signalling network. All parameters that are used specifically in the CSS7 signalling network are listed in this section. There are also short descriptions on their meanings. Parameter values vary depending on the system used and the release level.

The CSS7 signalling network-specific parameters are managed by using the commands NMO and NMC. The command NMO outputs the used parameter values in each parameter set. The command NMC is used to modify the used parameters.

The first parameter in the command defines the parameter set (J-M) of the parameter that you want to modify:

• J - network-specific parameters

• K - parameters for controlling international congestion

• L - parameters for controlling national congestion

• M - SLS parameters

The second parameter in the command defines the parameter you want to modify and its new value. Table 6 lists the parameter groups, parameters and their indexes, parameter names and their meanings, all possible values, and quality of parameter value and the recommended value, if any.



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Table 6. CCS7 signalling network-specific parameters


Value

J NETWORK SPECIFIC PARAMETERS

J0 CONGESTION_METHOD NO, INT, NAT, NATP

Three congestion methods exist: international method (INT), national method without prioritisation of signalling messages (NAT) and national method with prioritisation of messages (NATP).

INT method: The congestion criteria is the filling degree (1 limit) of the sending buffer whose limit values are defined in the Signalling Link Parameter File (SLNPAR). The congestion level directly follows the occupancy of the buffer. Timers T29 and T30 are used to control traffic restriction according to definitions made with parameters K0-K5.

NAT method: The congestion criteria is the filling degree (1 limit) of the sending buffer whose limit values are defined in the Signalling Link Parameter File (SLNPAR). Timers Tx and Ty determine the congestion level. The congestion level can have values 1-3, and traffic is restricted as required by the prevailing congestion level and as defined in parameters L1-L3.

NATP method: The congestion criteria is the occupancy (3 limits) of the sending buffer whose limit values are defined in the Signalling Link Parameter File (SLNPAR). The



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Value

congestion level determines how the messages are handled (for example, on congestion level 3, only messages with priority 3 or higher are routed forwards).

K INTERNATIONAL CONGESTION CONTROL METHOD PARAMETERS

K0 NB_OF_UP_LEVELS 1 ... 5

The amount of restriction levels for the originating traffic concerning the INT method.

K1 RESTRICT_PR_OF_UP_L1

0 ... 40 %

The restriction percentage for the originating traffic on restriction level 1. Timers T29 and T30 determine the restriction level. The default value is 40%.


20 ... 60 %



40 ... 80 %



60 ... 90 %


K5 RESTRICT_PR_OF_UP_L 80 ...100 %



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Value

5


K6 Q764_T29 30 ... 60

When the first congestion indication is received by the ISDN User Part (ISUP), the traffic load into the affected destination point code is reduced by one step. At the same time timers T29 and T30 are started. During T29 all received congestion indications for the same destination point code are ignored in order to not reduce traffic too rapidly. Reception of a congestion indication after the expiry of T29, but still during T30, will decrease the traffic load by one more step and restart T29 and T30. This step-by-step reduction of the ISUP signalling traffic is continued until maximum reduction is obtained by arriving at the last step. If T30 expires (for example, no congestion indications are no more received during the T30 period) traffic will be increased step-by-step and T30 will be restarted unless full traffic load has been resumed.

50

K7 Q764_T30 500 ... 1000

See K6. 600

L NATIONAL CONGESTION CONTROL METHOD PARAMETERS

L0 PREDETERMINED_CONG_LEVEL

1 ... 3

Defines the default value for the congestion level that



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Value

is reached when the buffer occupancy limit is exceeded for the first time, or when the congestion level is coded as 0 in a received TFC message.

L1 RESTRICT_PR_OF_MTP_L1

0 ... 50 %

The restriction percentage for originating traffic on congestion level 1.


20 ... 80 %



50 ...100 %


L4 Q704_TX 5 ... 200

The timer raises the congestion level when the filling limit of the transmit buffer has been exceeded. The smaller the parameter value is, the faster the congestion level is raised. (If the signalling link congestion status is set to s and the buffer occupancy continues to be above the set congestion threshold during Tx, the signalling link congestion status is updated by the new value s + 1.)

200 ms

L5 Q704_TY 5 ... 200

The timer lowers the congestion level when congestion has been on but then the filling degree of the sending buffer is decreased and goes below the set limit. The smaller the Ty is, the faster the congestion level decreases. (If the signalling



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Value

link congestion status is set to s and the buffer occupancy continues to be below the abatement threshold during Ty, the signalling link congestion status is updated by the new value s - 1.)

M SLS BITS

M0 LINK_SLS_BIT_MASK

Defines which SLS bits are used in load sharing within the link set.

ITU: 00001111 ANSI:

11111110

M1 ROUTE_SLS_BIT_MASK

Defines which SLS bits are used in load sharing between the routes.

ITU: 00001111 ANSI:

00000001

M2 SLS_LENGTH 4,5,8

Defines the length of SLS within the signalling network. In ITU networks, the SLS is 4 bits, while in ANSI networks it is 5 or 8 bits. ITU: 4 ANSI: 5 or 8.

6.3 Signalling Link Specific Parameters

The parameters in the signalling link specific parameter set define how the signalling links function. All signalling link-specific parameters are listed in this section. There are also short descriptions on their purposes. Parameter values vary depending on system and release level.

The signalling link -specific parameters are managed by using the commands in the command group NO. The commands can be used to modify existing parameter sets or to create new ones. Before you start modifying an existing parameter set, check that all signalling links using this parameter set have been deactivated. The new values become effective when the links are activated again. To create a new parameter set, you can replicate (copy and rename) an old parameter set and modify its values.



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The command NOI outputs the values of parameters belonging to the defined sets, and the command NOM can be used to modify the parameter values in an existing parameter set.

In the command, the name and number of the parameter set are defined. In addition, the identifier of the parameter group is defined according to the parameter that you want to change:

• A - miscellaneous parameters on MTP level 2

• B - control parameters for the error ratio on MTP level 2 (as defined by ITU)

• C - timer parameters for MTP level 2 (as defined by ITU)

• D - miscellaneous parameters on MTP level 3

• E - signalling congestion control parameters

• F - timer parameters for MTP level 3

The second parameter in the command defines which parameter from the parameter set you want to modify, and gives the new value. Table 7 lists the parameter groups, parameters and their indexes, parameter names and their meanings, all possible values, quality of the value and the recommended value, if any

Table 7. Signalling link specific parameters


Value

A MISCELLANEOUS MTP LEVEL 2 PARAMETERS

A0 LI_CODING STANDARD, BTNR

Controlling the LI coding. BTNR is a specific method in BTNR Spec. (UK).

STANDARD

A1 BIT_D_CODING_IN_LSSU STANDARD, BTNR

Controlling the D bit coding in the LSSUs. BTNR is a specific method in BTNR Spec. (UK).

STANDARD

A2 BIT_D_CHECK_IN_LSSU YES, NO

Controlling the D bit checking in the received LSSUs. (1H Bit D checked from the received LSSU).

YES

A3 L2_ERROR_CORRECTIO BASIC, PCR



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Value

N

Controlling the error rate monitoring in the transmission direction. PCR is for preventive cyclic retransmission for satellite links.

BASIC

A4 SN_RANGE 40…4095

Maximum value for backward sequence number and forward sequence number of signalling unit.

127

A5 JT_Q703_K 40…127

Defines the number of transmitted MSU messages without positive acknowledgement. This parameter is relevant only in Japanese signalling network.

40

B MTP LEVEL 2 ERROR RATE MONITORING PARAMETERS

B0 SUERM_T 8 ... 512

Controlling the error rate of the message unit: SUERM_T, SUERM_D and SUERM_N (see CCITT Q703 10.2).

64

B1 SUERM_D 16 ... 1024


256

B2 SUERM_N 8 ... 24


16

B3 AERM_TIN 1 ... 16

Controlling the error rate of the alignment AERM_TIN,

4



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Value

(see CCITT Q703 10.3).

B4 AERM_TIE 1 ... 8

Controlling the error rate of the alignment AERM_TIE (see CCITT Q703 10.3).

1

B5 AERM_M 1 ... 16

Controlling the error rate of the alignment AERM_M (see CCITT Q703 10.3).

5

B6 AERM_N 8 ... 24

Controlling the error rate of the alignment AERM_N (see CCITT Q703 10.3).

16

B7 PCR_N1 (preventive cyclic retransmission)

1 ... 127

PCR_N1, number of MSUs that can be resent.

127

B8 PCR_N2 300 ... 6000

PCR_N2, number of MSUs that can be resent.

800

B9 EIM_TE 8 ... 793544

Error interval monitor parameter (see ITU-T Q703 A.10.2)

99193

B10 EIM_UE 1 ... 198384


24798

B11 EIM_DE 1 ... 11328


1416

B12 JT_Q703_TE 20 ... 30 (1 ms)

Defines the normalized time for error rate monitoring. This parameter is relevant only in Japanese signalling network.

24

C MTP LEVEL 2 TIMER



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Value

PARAMETERS

C0 Q703_T1 130 ... 500 (0.1s)

Q703_T1, Alignment Completed timer.

400

C1 Q703_T2 50 ... 1500 (0.1s)

Q703_T2, No Alignement timer.

100

C2 Q703_T3 10 ... 116 (0.1s)

Q703_T3, Alignment timer. 10

C3 Q703_T4 23 ... 95 (0.1s)

Q703_T4, Length of Test Period timer.

82

C4 Q703_T5 8 ... 30 (0.1s)

Q703_T5, SIB Transmission timer.

10

C5 Q703_T6 30 ... 72 (0.1s)

Q703_T6, Remote End Congestion timer.

50

C6 Q703_T7 5 ... 20 (0.1s)

Q703_T7, Delayed Acknowledgement timer.

10

C7 Q703_T8 8 ... 12 (0,01 s)

Error interval monitor timer 10

C8 JT_Q703_TF 20 ... 30 (1 ms

Defines interval for sending FISU when there is no MSUs transmitted. This parameter is relevant only in Japanese signalling network.

24

C9 JT_Q703_TO 20 ... 30 (1 ms)

Defines interval for transmitting SIO and SIE messages used for initial set-up and during verification. This parameter is relevant only in Japanese signalling network.

24



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Value

C10 JT_Q703_TS 10 ... 30 (1 ms)

Defines interval of SIOS to be transmitted during suspension. This parameter is relevant only in Japanese signalling network.

24

D MISCELLANEOUS MTP LEVEL 3 PARAMETERS

D0 PERIODIC_LINK_TEST_DENIED

YES, NO

Controlling the transmission of signalling link test messages.

NO

D1 MAX_LENGTH_OF_SIF 272

Maximum length of the SIF field in the MSU message.

272

D2 INHIBIT_ATTEMPT_LIMIT 1 ... 5

Limit for repeated attempts to inhibit a link.

3

D3 INHIBIT_TEST_DENIED YES, NO

Controlling the inhibition of a test procedure.

NO

D4 ECO_SENDING_ALLOWED

YES, NO

Defines the control of Emergency Changeover procedure.

ITU-T: YES ANSI: YES

JAPAN: NO (NTT), YES (TTC

D5 INHIBITION DENIED YES, NO

NO

D6 SIN DENIED YES, NO

NO

D7 SIPO DENIED YES, NO

NO

D8 LINK SUSPEND DENIED YES, NO

YES

D9 FALSE CONG DENIED YES, NO

YES



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Value

D10 LINK SRT DENIED YES, NO

YES

E SIGNALLING CONGESTION CONTROL PARAMETERS

E0 CONG_FILTERING_TIME 10 ... 100 (0.01s)

Defines the time after which continuing congestion on a signalling link is reported to level 3. This feature keeps the signalling traffic control procedures from starting during very short-time peak loads. 30 (0.3s).

1

E1 BUFF_FILTERING_TIME 50 ... 300 (0.01s)

Defines the time after which continuing congestion on a signalling link is reported to level 3 while signalling message buffering is active. This feature keeps the signalling traffic control procedures from starting in special situations such as changeovers, changeback, and controlled rerouting. 150 (1,5s).

1

E2 CONG_ONSET_THRESHOLD1

2 ... 1000

Reports the occupancy of the transmission buffer that is interpreted as level 1 congestion. Congestion can be set for threshold values 0-127; if the value is 128-255, signalling link congestion is never on. The limit for congestion onset (messages) is 49.

49

E3 CONG_ABATE_THRESHOLD1

1 ... 800

Reports the occupancy of the transmission buffer that is interpreted as ending for level 1 congestion (that has been on). It is advisable to

2



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Value

set the release level of congestion lower than the activation level to avoid vibrations. The limit for congestion reset (messages) is 2.

E4 CONG_DISC_THRESHOLD1

0 ... 2500, NOT IN USE

Reports the occupancy of the transmission buffer that enables the signalling terminal software to set the signalling message. This sets the destroy status in the transmission mailbox. When the CCSEND program block notices that the destroy status is set, it destroys the signalling messages addressed to the mentioned signalling terminal. The threshold values for the destroy status are selected from the range 0-127; if the value is 128-255, the status is not set. However, when the transmission buffer fills up, signalling messages have to be destroyed. The status value must therefore be higher than the limit for signalling link congestion in order to avoid unnecessary message destruction. The limit for message discarding (messages) is NOT IN USE.


2 ... 1000, NOT IN USE

CONG_ONSET_THRESHOLD2,CONG_ABATE_THRESHOLD2,CONG_DISC_THRESHOLD2,CONG_ONSET_THRESHOLD3,CONG_ABATE_THRESHOLD3 and CONG_DISC_THRESHOLD3 are similar to the above-mentioned parameters when the congestion control method that is used has several levels. The



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Value

parameter values on level 2 must be higher than the corresponding values on level 1, and values on level 3 must be higher than those on level 2 in order to get the congestion method to work properly. When the congestion method uses only one level, set the parameter values on levels 2 and 3 as 255 = 0FFH. See parameters E2, E3.

E4 & E6 CONG_ABATE_THRESHOLD2

1 ... 800, NOT IN USE See parameters E5 and E3

E7 CONG_DISC_THRESHOLD2




E9 CONG_ABATE_THRESHOLD3


E10 ONG_DISC_THRESHOLD3


E11 T111_T31_ONSET_THRESHOLD

1, 2, 3, NOT IN USE

Congestion threshold for starting timer T111_T31.

0

E12 T111_T31_RESET_THRESHOLD

1, 2, 3, NOT IN USE

Congestion threshold for resetting timer T111_T31.

0

E13 SL_LOAD_THRESHOLD 100 ... 900

Allows maximum value for signalling link load in Merlangs without notification.

200

F MTP LEVEL 3 TIMING PARAMETERS

F0 Q704_T1 5 ... 12 (0.1s)

Delay to avoid message mis-sequencing on changeover.

8

F1 Q704_T2 7 ... 20 (0.1s)

Waiting for changeover 14



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Value

acknowledgement.

F2 Q704_T3 7 ... 12 (0.1s)

Time controlled diversion-delay to avoid mis-sequencing on changeback.

8

F3 Q704_T4 5 ... 12 (0.1s)

Waiting for changeback acknowledgement (first attempt).

8

F4 Q704_T5 5 ... 12 (0.1s)

Waiting for changeback acknowledgement (second attempt).

8

F5 Q704_T12 8 ... 12 (0.1s)

Waiting for un-inhibition acknowledgement.

10

F6 Q704_T13 6 ... 15 (0.1s)

Waiting for force un-inhibition acknowledgement.

10

F7 Q704_T14 8 ... 30 (0.1s)

Waiting for inhibition acknowledgement.

20

F8 Q704_T17 8 ... 60 (0.1s)

Delay to avoid oscillation of initial alignment failure and link restart.

10

F9 Q704_T22 180 ... 600 (1s)

Local inhibit test timer. 180

F10 Q704_T23 180 ... 600 (1s)

Remote inhibit test timer. 180

F11 Q707_T1 8 ... 120 (0.1s)

Waiting for signalling link test message acknowledgement.

80

F12 T111_T19 120 ... 600 (1s)

Time supervision for setting an alarm about a signalling link that refuses to start up, as defined in ANSI

120



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Value

standards.

F13 T111_T20 90 ... 120 (1s)

Control for local inhibition testing as defined in ANSI standards.

120

F14 T111_T21 90 ... 120 (1s)

Control for remote end inhibition testing as defined in ANSI standards.

120

F15 T111_T31 10 ... 120 (1s)

False link congestion detection timer.

10

F16 T111_T32 5 ... 120 (1s)

Link oscillation timer - Procedure A.

5

F17 JT_Q704_TS 0 ...600 (1 s)

Defines the time for transmitting SIOS on a periodical basis during suspension. This parameter is relevant only in Japanese signalling network.

30

F18 JT_Q707_T10 0..600 (0.1s)

This parameter is relevant only in Japanese signalling network.

100

F19 ALIGN_RESPONSE_WAIT 40

6.4 Signalling Route Set Specific Parameters

The parameters included in the parameter set of the signalling route set are used to handle the functions of the whole Message Transfer Part (MTP). This section introduces all parameters that are specific to each signalling route set and describes their purposes briefly. The parameter values vary depending on the used system and release level.

The signalling route set-specific parameters are managed using the commands in the command group NN. You can use the commands to



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create new parameter sets or to modify the values of individual parameters included in the parameter sets. When you have modified the values of existing parameters, the new values become effective immediately. To create a new parameter set, you can replicate (copy and rename) an old parameter set and modify its values so that they suit the present needs.

The command NNI outputs the values of the parameters in the selected parameter sets. The command NNM is used to modify the parameter values in an existing parameter set.

In the command, the name and number of the parameter set are defined. In addition, the identifier of the parameter group is defined according to the parameter that you want to change:

• A – Common timers for all destinations

• B – Signalling point restart timers

• C – Adjacent signalling point parameters

• D – Common parameters of all signalling points

Table 8. Signalling route set specific parameters (* -parameter valid locally only)


Value

A COMMON TIMERS OF ALL DESTINATIONS

A0 Q704_T6 5 ... 20 (0.1s)

Delay to avoid message mis-sequencing on controlled rerouting. The parameter sets the time that is waited during controlled rerouting before traffic is activated to the destination point via a new or alternative transfer point.

8

A1 Q704_T8 5 ... 20 (0.1s)

Time supervision for inhibition of the Transfer Prohibited messages. The Transfer Prohibited messages generated by the reply system are not sent to the destination point, if other—similar—messages have been sent there during the time

10



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Value

specified by the parameter.

A2 Q704_T10 10 ... 120 (1s)

Time supervision for repetition of test messages in the signalling route set. Test messages related to another signalling point are sent at intervals defined by the time parameter.

31

A3 Q704_T11 30 ... 90 (1s)

Transfer restricted time supervision. This parameter sets the time for how long a signalling link set, that uses another signalling point as the transfer point, has to be faulty before it is set in a long-term failure state. When this state is set for a signalling link set, transfer restricted messages are sent to the adjoining signalling points. The messages concern all route sets where one of the primary routes has been using the failed link set and where the traffic is now directed to secondary routes.

60

A4 Q704_T15 20 ... 30 (0.1s)

Signalling point Z receives another transfer-controlled message related to the same destination within T15 after the reception of the last transfer-controlled message related to destination X.

If the value of the congestion status carried in the new transfer controlled message is higher than the current value of the congestion status of the signalling route set towards destination X, then the current value is updated to the higher one.

25



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Value

If T15 expires after the last update of the signalling route set toward destination X in a transfer-controlled message related to the same destination, the signalling-route-set-congestion-test procedure is invoked.

A5 Q704_T16 14 ... 20 (0.1s)

If a Transfer Controlled message related to the concerned destination is received within T16 after sending a signalling-route-set-congestion-test message, the signalling point updates the congestion status of the signalling route set.

If T16 expires after sending a signalling-route-set-congestion-test message without a Transfer Controlled message related to the concerned destination having been received, the signalling point changes the congestion status associated with the signalling route set.

15

A6 T111_T18 2 ... 20 (1s)

A signalling point starts the MTP restart procedure when its first link is in service at level 2. Restarting the MTP: - if it has the transfer function, it starts timer T18;

3

A7 JT_Q707_T10 100

B SIGNALLING POINT RESTART TIMERS

B0 * Q704_T21/T111_T25 20.70 (1s)

Q704_T21: The waiting period before traffic is restarted via an adjacent signalling point. Traffic on the routes using the

Blue Book 31

White Book 64



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Value

adjacent signalling point is started only when the time defined in this parameter has past after the restart of the adjacent point (or when the point has sent the Traffic Restart Allowed message). T111_T25: Waiting for the Traffic Restart Active message.

ANSI 64

B1 T111_T28 3..35 (1s)

Signalling point X starts timer T28 either when the first signalling link goes into state In Service on level 2, or when the first signalling link becomes available on level 3.

This parameter is used only in networks built according to the ANSI standards.

30

B2 Q704_T19_WHITE/T111_T29

60 ..80 (1s)

Supervision timer during the MTP restart to avoid possible ping-pong (back and forward) of TFP, TFR and TRA messages.

68

B3 * T111_T30 20 ... 40 (1s)

If the receiving point has the transfer function, it starts timer T30 and then sends a Traffic Restart Waiting message followed by the necessary Transfer Restricted and Transfer Prohibited messages. Preventive Transfer Prohibited messages are required for traffic currently being routed via the point from which the unexpected Traffic Restart Allowed or Traffic Restart Waiting messages were received. It also sends a Traffic Restart Allowed message.

30 ANSI

C ADJACENT SIGNALLING



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Value

POINT PARAMETERS

C0 * TRM_DENIED YES, NO

Use of message pair TRA/TRW is denied in network management. In an ANSI network, the use of TRW in connection with the SP restart is denied.

NO

C1 * TRM_EXPECTED YES, NO

This parameter controls the use of message pair TRA/TRW. TRA_EXPECTED means that traffic restart is allowed. When the signalling link set is used, it controls the wait for the message reception. TRA_WAITING controls the waiting of message reception when the signalling link set is taken into use. TRA_DENIED means that sending of Traffic Restart Allowed messages is denied.

YES

C2 * SP_RESTART_TYPE BLUE, NONE /WHITE/ANSI

Controlling the denial of the signalling point restart procedure. When this procedure is denied, the restart procedure of the adjacent signalling point is not used. When its own signalling point is restarted, the Traffic Restart Allowed message is not sent to the adjacent SP, either.

BLUE

C3 * INDIRECT_ROUTES_DEFAULT

AVAILABLE, RESTRICTED, UNAVAILABLE, TFM BASED

Parameter for controlling the signalling link set restarts in situations when the adjacent SP has not been started. The possible parameter values are available, restricted,

AVAILABLE



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Value

unavailable, and TFM based.

C4 * TFM_CONTROL ALL ALLOWED, BROADCAST DENIED, ALL DENIED

Control parameter for broadcasting messages: Transfer Allowed, Transfer Restricted, and Transfer Denied. When the parameter denies broadcasting of messages, and an SP becomes either available or unavailable, it is not reported to the adjacent SP.

ALL ALLOWED

C5 * RESP_TFM_CONTROL TFR ALLOWED, TFP ALLOWED, TFPFOR KNOWN, TFM DENIED

Control parameter for the response method messages. Possible parameter values are TFR allowed, TFP allowed, TFP for known, and TFN denied.

TFP ALLOWED

C6 * TFR_DENIED YES, NO

Control parameter for the use of the Transfer Restricted procedure. If the use of this procedure is denied, the Transfer Restricted messages coming from the source point are not handled, and Transfer Restricted messages are not sent to the destination point. Instead, the system sends Transfer Allowed messages (unless their use is also denied).

YES

D COMMON PARAMETERS OF ALL SIGNALLING POINTS

D0 TFR_SENDING_BASIS NONE, ITU, ANSI

Control parameter for managing overload on a spare route when the last available route becomes

NONE



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Value

unavailable. Possible parameter values are NONE (no TFR messages broadcast), ITU (follows ITU-T Rec. Q704), and ANSI (examines state of timer T11).

D1 CIRC_ROU_PREV_IN_USE

YES, NO

Control parameter for restricting the occurrence possibilities of circularly routed messages. When this parameter has the value YES, an extra Transfer Prohibited message is used for one of the destination signalling points. If traffic to the point travels via alternative routes, the system sends the Transfer Prohibited message about that point to all adjoining signalling points. It then orders all traffic to switch to the point via other signalling points.

NO

D2 TFC_DENIED YES, NO

Control parameter for the Transfer Controlled message. If the parameter has the value NO and denies the message, the Transfer Controlled messages are not sent to the destination point.

NO

D3 CONG_LEVEL_SUPPORT NONE, TFC

Control parameter for the Transfer Controlled messages congestion level encoding. If the parameter has the value NO and the message control is inactive, the system sets congestion level 0 for the TFC messages directed to the destination point. Otherwise they get a congestion level that is defined by the over loaded signalling terminal. This

TFC



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Value

control parameter can also be used to define the overload of a destination point to be monitored using the Congestion Level Test messages.

D4 CONFUSION_MSG_DENIED

YES, NO

Control parameter for the MTP Confusion message. If sending the messages is prohibited, the messages are not transmitted to the destination point. This feature is implemented as defined in standard BTNR 146.

YES

D5 UPU_ALLOWED YES, NO

This parameter either allows (YES) or denies (NO) UPU message sending.

NO

D6 RST_ON_TFP_ALLOWED YES, NO

This parameter either allows (YES) or denies (NO) immediate sending of route set test (RST) message when transfer prohibited message (TFP) is received. When this parameter has value NO, the RST message is sent after the Q704_T10 timer has expired.

ITU: YES

ANSI: YES

JAPAN: NO

D7 SUPPORT_OF_M3UA_NW_APP

YES, NO

Control of using Network Appearance parameter in the "M3UA signalling network management messages".

YES

D8 USE_OF_M3UA_NW_SNM

YES, NO

Control of sending M3UA signalling network management messages.

NO

MTP Parameters HandlingAppendix


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Value

D9 SRT DENIED YES, NO

D10 USN DENIED YES, NO

Appendix


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Appendix

References


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References

Glossary


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Glossary

Index


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Index

02_MTP

Documents

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primary process

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message pair

process family

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