MTP Document

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Switching Core NetworkSignalling

Message Transfer PartTraining Document M14/U4

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Contents

Contents

Summary of changes.............................................................................4

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

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

3 Signalling network................................................................................8

4 MTP layers..........................................................................................10

5 MTP alarms.........................................................................................40

6 MTP parameters handling..................................................................42

Appendix...............................................................................................73

References............................................................................................74

Glossary................................................................................................75

Index 76


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Summary of changes

Summary of changes


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MTP parameters handlingAppendix

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


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2 Introduction

The CCS#7 Structure divides the signalling functions into MessageTransfer Parts and the User Parts for different users andapplications.

The user part communicates with a corresponding user part in the

adjoining network element.

The MTP serves as a common transport system that provides reliabletransmission of the signalling messages between the communicatinguser parts, regardless of the unreliability of the physical transmissionmedia. MTP is covered under ITU-T specifications Q.701 707. Thefunctions 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 themeans to access it. The level 1 function provides a bearer for asignalling link.

The signalling link function(level 2) defines the functions consideringmessage transfer between two adjacent network elements through asignalling link. It defines the message structure, framing, error detectionand 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 tothe respective user part, and network management, which provides all

the necessary procedures for using the signalling network in an optimalway.


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MTP2

MTP3

Layer 4

(User Part) ISUP TUP SCCP Other User Parts

Signalling

MTP2

MTP1

Signalling Link

Function

Signalling Data Link

Function

Signalling Message

Handling

Signalling Network

Management

Control signals Signalling message flow

Figure 1. MTP Layers


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3 Signalling network

A signalling network comprises of signalling points. A distinction is madebetween 2 categories:

Signalling end points (SEP)

Signalling transfer points (STP)The signalling end points are the sources (origination points) anddestinations (destination points) of the signalling traffic. Incommunications network both these points are usually switchingcenters.

On the basis of the destination address, the signalling transfer pointsforward received signalling messages to another signalling transfer pointor, where applicable, to a signalling end point. No processing of themessage content takes places in a signalling transfer point. A signallingtransfer point may be integrated in a signalling point (e.g. a switchingcent) 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 cantherefore be addressed specifically in a signalling message.

The signalling point code is a 14 bit value (ITU-T SS7 standard) and canbe 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 (016383) is insufficient toaddress all signalling points worldwide, it is always used together withthe network indicator. The network indicator has four values: NA0,NA1, IN0, and IN1.


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SEP

STP

Signalling link

Signalling link

SEP

SEP SEP

Signalling

end point

Signalling

end point

Signalling

end point

Signalling

end point

Signalling

transfer point

DPC = X

Signalling link

DPC = X

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

Signalling Point Codes

National useLength: 14 bits (ITU-T SS7 standard), 16 bits (JapanSS7 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 IndicatorNA0 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 andfunctional characteristics and the physical interface (E1 or T1) towardsthe transmission media.

In digital systems normally 64 kbps or 56 kbps channels are used, thatis, a timeslot of PCM30 or PCM24 respectively. The choice of thetimeslot may be any timeslot except TS 0. These are governed by theG.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 forand relating to the transfer of signalling messages over one individualsignalling data link. The level 2 functions, together with a level 1signalling data link as a bearer, provide a signalling link for reliabletransfer of signalling messages between two directly connectedsignalling points.

Signalling messages delivered by superior hierarchical levels aretransferred over the signalling link in variable length signal units. Thesignal units include transfer control information for proper operation ofthe 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

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


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

5. signalling link failure detection by means of signal unit error ratemonitoring and signalling link recovery by means of specialprocedures

Level 2 functions are specified in Recommendation Q.703.

User Part

Level 1

Flag Detection and

Bit-stuffingFlag Detection and

Bit-stuffing

ControllerController

Retransmission

BufferRetransmission

Buffer

Message Length

CheckMessage Length

Check

Checksum

Generation andComparison

Checksum

Generation andComparison

Sequence NumberCheck

Sequence Number

Check

Received BufferReceived Buffer

Flag Generation

and Bit-stuffingFlag Generation

and Bit-stuffing

ChecksumGeneration

Checksum

Generation

Sequence NumberGeneration

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 ofvariable length towards destination. A signal unit is formed by thefunction of level 2. In addition to the message it also contains controlinformation for the message exchange.

There are three different types of signal units:

1. Message signal units (MSU)


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2. Link status signal units (LSSU)

3. Fill-in signal units (FISU)

Types of signal units are differentiated by means of the length indicatorcontained in all signal units. Message signal units are used for thetransport of the user part messages. Link status signal units containinformation about state of the signalling link. Fill-in signal units containno additional information. It is used when there is no message to be senton the link. Own side has no messages to send, but the remote endexpects acknowledgements for the message signal units that it has sent.

Message signal units are retransmitted in case of error; link status signalunit and fill-in signal unit are not. The basic formats of the signal unitsare 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 thestart of a signal unit. The opening flag of one signal unit is normally theclosing flag of the preceding signal unit. The bit pattern for the flag is0111 1110 or 7Eh. The flag is also used for alignment of the signallinglink at the far-end.

Bit stuffing for Flag imitation prevention is done by inserting a 0 after5 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 forerror correction.

Forward sequence number (FSN)

It is the sequence number of the signal unit in which it is carried. FSNand 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 orwhether it is being retransmitted.


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F CK SIF SIO LIF

I

B

FSNB

I

B

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 LIF

I

B

FSNB

I

B

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 LIF

I

B

FSNB

I

B

BSN F

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

FISU First bittransmitted

length indicator = 0

F Flag

BSN Backward Sequence Number

BIB Backward Indicator Bit

FSN Forward Sequence Number

FIB Forward Indicator Bit

LI Length Indicator

SIO Service Information Octet

SIF Signalling Information Field

CK Check Bits

SF Status Field

Figure 5. Signal unit formats

Length indicator (LI)

The length indicator is used to indicate the number of octets followingthe length indicator octet and preceding the check bits. Length indicatoris a number in binary code in the range of 0-63. It differentiates betweenthe 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. Itcontains the service indicatorand the subservice field.

Signalling information field (SIF)

The signalling information field only exists in message signal units. Itcontains 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 thecalculated and received checksums do not match, a negativeacknowledgement is conveyed by setting BSN to the received FSN andinverting the previously transmitted BIB. This BIB will remain in the newstate till a new error occurs.

Status field (SF)

The status field only exists in link status signal units. It contains statusindications of the signalling link. Only three bits are used to representsignal status. The possible state and corresponding messages arestated 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 methodand thepreventive cyclicretransmission method. Both error correction techniques apply only toMSU but not to LSSU and FISU.

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

Retransmission Buffer

Signalling TerminalSignalling Terminal

MSU

Negative Acknowledgement

Retransmission

Figure 7. Basic error correction method

The preventive cyclic retransmission method is implemented on longdistance lines, with transmission time greater than 15ms. Negativeacknowledgement is not awaited., instead all unacknowledged and newsignalling units are kept in the retransmission buffer and transmittedperiodically. The remote end simply waits for the retransmission tocorrect the error.

Send only positiveacknowledgement of

MSU

Retransmission Buffer:

Delete a positiveacknowledgement elsecyclically 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 ofSignal Unit Error

Rate Monitoring (SUERM). This is a statistical method of ensuring thepermitted error rate on a link. SUERM is a counter, which increments ona detection of error. If 256 signalling units are received error free itdecrements by one. This is called the leaky bucket principle. If theSUERM counter reached the pre-set threshold (generally 64), then linkis 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, andcongestion control.

4.2.4.1 Initial alignment procedure

The initial alignment procedure is used for link activation and restorationeither 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 asacknowledgement 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 tosend 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 linkone by one.

Link proving

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

Normal proving

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

Emergency proving

If SIE was the LSSU exchanged, 212 octets are exchanged via thesignalling link within a time of 0.5 sec with only one SU allowed tobe 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 beginningof an alignment period. Every SU in fault increments the counter by one.If threshold (four or one) is reached before the exchange of pre-requisiteoctets, start a new alignment period. If five periods fail, the link is markedfaulty.

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 theDPC, OPC, SLC, and a test pattern. It is acknowledged from the otherside by Signalling Link Test Acknowledgement message (SLTA) with thesame

bit-pattern. If the test pattern is received correctly, the Link State ismarked as available executing and the link can be used for signalling.


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Activate link

SIO

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

serviceIdle

Aligned

In

service

Proving

SIO

Link 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 3and / 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 receivedMSUs are discarded. FISU are exchanged continuously.

4.2.4.3 Congestion control

In case there is congestion on the receiving side of the signallingconnection, an LSSU (SIB) is sent every 200msec, until congestion

ceases. MSU and FISU continue to be transmitted as usual. The BSNand BIB values do not change, but show the last acknowledged MSU.

If congestion persists beyond 10 seconds, the link is declared faulty andan 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 ensurethat the signaling messages originated by a particular user part at asignaling point (originating point) are delivered to the same user part atthe destination point indicated by the sending user part.

The signalling message handling functions are based on the labelcontained in the messages which explicitly identifies the destination and

originating points. The label part used for signalling message handlingby 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 itconsists of 3 main parts: the service information octet (SIO), routinglabel and user information field.


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The destination of a signal unit is specified in a routing label. The routinglabel is a component of every user message and is transported in thesignalling information filed (SIF). The routing label consists of

destination point code (DPC), originating point code(OPC), andsignalling link selection (SLS) field.

The service information octet (SIO) contains additional addressinformation. Using the service indicator (SI), the destination messagetransfer part identifies the user part for which message is intended. Thesubservice field (SSF) contains the network indicator which enables amessage to be identified, for example, as being for national orinternational traffic.

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

[bit]

SLS OPC DPC

User InformationRouting

LabelSIO

SubserviceField (SSF)

ServiceIndicator (SI)

Signalling Information Field (SIF)

4 14 14 4 4

First bit

transmitted

OPC Originating Point Code

DPC Destination Point Code

SLS Signalling Link Selection

0000 (0H): SNM0001 (1H): SNT

0011 (3H): SCCP0100 (4H): TUP0101 (5H): ISUP

1101 (DH): BICC

00XX (0H) : IN001XX (4H) : IN1

10XX (8H) : NA011XX (CH) : NA1

Figure 12. MTP3 message structure and coding

The command group NP SERVICE INFORMATION DATA HANDLINGis used to create, modify, delete, and interrogate the signalling serviceinformation data of own signalling point.

Execution ofZNPIcommand gives the following printout:


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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 signallingnetwork.

Service indicator name

1 - 5 ASCII characters

Service existing for STP messages

The parameter may receive the following values:

Y it is desired that service exists for STP messages


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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 incomingsignalling messages of the user part of one's own signalling point. Theparameter is obligatory if service is created for the incoming signallingmessages of the user part of one's own signalling point but the

parameter cannot be given if no service is created for incomingsignalling 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 theincoming signalling messages of the user part of one's own signallingpoint. The parameter is not obligatory, and it cannot be given if noservice is created for the incoming signalling messages of the user partof 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 signallingpoint, the parameters PRIMARY PROCESS FAMILY and SECONDARYPROCESS FAMILY cannot be given.

If service is created for incoming messages in the user part of ownsignalling point, the parameter PRIMARY PROCESS FAMILY must begiven.

If SERVICE INDICATOR INDEX = 0 and service is created for incomingmessages in the user part of one's own signalling point, the default ofPRIMARY PROCESS FAMILY is the process family indicator ofCCNETM and the default of SECONDARY PROCESS FAMILY is theprocess family indicator of CCDESM.

If SERVICE INDICATOR INDEX = 1 and service is created for incomingmessages in the user part of one's own signalling point, the default of


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PRIMARY PROCESS FAMILY is the process family indicator ofCCNETM. PRIMARY PROCESS FAMILY and SECONDARY PROCESSFAMILY cannot have the same value (family process indicator).

4.3.2 Signalling message handling

Signalling message handling is responsible for the routing of messagesto the appropriate link, and distribution of the received messages withinown 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

The discrimination function evaluates the destination point code(DPC) of the MSU. If the DPC of the received message is equal to own


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SPC the message is sent to the distribution function. Otherwise it is sentto 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 thesignal unit to another network element. The routing is based on DPC,SIO, and the SLS carried in the message. The SLS in turn defines loadsharing, and thus link selection.

4.3.2.1 Load sharing within a linkset

Load sharing within a linkset is based on use of SLS bits (4 bits afterOPC in routing label). For example in ISUP messages SLS bits arecopied 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. Loadsharing is performed between all available signalling links in a linkset.

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

SLS

LINK

Figure 15. Load sharing within a linkset


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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 routeand 0 the lowest priority route.

Load sharing between link sets is independent from load sharing within alink 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 200implementation, 8 link sets can belong to a route set (8 routes). Routepriorities are significant because traffic is shared on the routes withsame priority. If only one route has highest priority (usually the directroute), no load sharing occurs. Priority is also used in forced rerouting todetermine the alternative route. Load sharing between link sets alsouses all 4 bits of a SLS. If route priorities are the same and load sharingis allowed load sharing is as follows:

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 normalsignalling conditions in the event of disruption in the signalling network,either in signalling links or at signalling points. The disruption may be inthe form of complete loss of a signalling link or a signalling point, or inreduced accessibility due to congestion.

There are 2 categories of signalling network management messages asindicated 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. Itcomprises of two parts H0 and H1, 4 bits each, which identify themessage. The message structure is shown on the Figure 17.

F CK SIF SIO LIF

I

B

FSNB

I

B

BSN F

4 4 4 14 14 4 4 [bit]

MSU First bittransmitted

User Information H1 H0 SLS OPC DPC SSFSI

0000

SSF Subservice Field

H0 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 subfieldin SIO. H0 and H1 indicate the type of message being sent. Figure 18illustrates the heading code allocation of SNM messages.


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CNPCNSCSSDLC1000DLM

H1

UPU1010UFC

TRA0111TRM

LRTLLTLFULIDLUALIALUNLIN0110MIM

RSRRST0101RSM

TFATFRTFP0100TFM

TFCRCT0011FCM

ECAECO0010ECM

CBACBDCOACOO0001CHM

0000

10000111011001010100001100100001

H0

GROUP

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 testpattern. The SNT messages are coded as 0001 in the Service indicatorsubfield 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

The signalling network management is divided into 3 functions:


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1. Signalling traffic management function

The signalling traffic management is responsible for the availabilityof 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 signallinglinks and is responsible for the state changes by using thefollowing 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 adestination by using the following procedures:

transfer-prohibited procedure, indicating the unavailability of

a destination

transfer-allowed procedure, indicating the availability of adestination

transfer-controlled procedure, indicating the overload

situation of a destination

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

signalling route set.

4.3.4 Signalling traffic management procedures

4.3.4.1 Changeover procedure

In case of a signalling link failurethe traffic from failed link is diverted toall other remaining links in a linkset, avoiding at the same time loss of


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messages, duplication or wrong order.When a signalling link fails theload sharing table is calculated again.

Changeover order signal (COO) is sent to the remote end via one of

available signalling links inside the signalling linkset. It indicates the SLCof 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 signallingmessages for this link are buffered in the delay buffers ofalternative signalling links x, y...

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

The remote end proceeds in the same way.

The reception of a changeover message is acknowledged bysending a changeover acknowledge message (COA).

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

After the retrieval the contents of delay buffers are released andthe 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 transferof the signalling from the alternative signalling links to a signalling linkthat has become available again is successful, while avoiding at thesame time loss, duplication or missequencing of messages.

Procedure:

Automatically the traffic is returned to the now available signalling

link.

The signalling link selection table is updated and the newinformation is distributed to all CCSUs.

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


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A B

SLC = 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. Changeover 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

4.3.4.3 Emergency changeover procedure

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


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Procedure:

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

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

In cases of receiving either ECO or ECA, the retransmission bufferis not updated. Instead only new messages are transmitted. Hencesome 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 pointacting as a signalling transfer point (STP) for messages relating to agiven destination, when it has to notify one or more adjacent signallingpoints that they must no longer route the concerned messages via thatsignalling transfer point.

The transfer-prohibited procedure makes use of the transfer-prohibited(TFP) message which contains routing label, transfer-prohibited signaland 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 routebetween B and D is not longer available and neither B nor D haveany alternative route to reach the destination), B and D send aTransfer Prohibited message including the DPC of the networkelement, which is no longer reachable to the adjacent signallingpoints.

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 reroutingprocedure is activated.

Procedure:

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


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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 traffic

to 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 totest 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, andthe 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

Procedure to check availability of the route:


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On reception of a TFP message initiates the signalling route setprocedure.

C and E periodically send an RST message to B and D

respectively. This message contains the same DPC as thereceived 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 checkthe availability of the route.

In case the signalling point of the message is still unavailable thereis 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, actingas signalling transfer point for messages relating to a given destination,

when it has to notify one or more adjacent signalling points that theymay start to route to it.

The transfer-allowed procedure makes use of the transfer-allowedmessage 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 adjacentsignalling 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 isavailable 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 previousunavailable route becomes available again.

It has to be distinguished between 3 different cases:

In the case the route that becomes available again has a higherpriority than the route actually used, the controlled reroutingprocedure is performed.

In the case the route that becomes available again has the samepriority as the route actually used and load sharing is allowed, thetraffic is spread over both routes.

In the case the route that becomes available again has the samepriority as the route actually used and load sharing is denied, thetraffic 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 maystart from an OPC or from a STP. It is sent in every 8th message to theDPC. The TFC message results in informing level four to slow down thesignalling messages to the mentioned destination.

4.3.5.7 User part availability control

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

When the originating signalling points MTP receives a UPU message, itsend an indication to the local user designated in the message. The usershould then take appropriate action in order to stop generation of normalsignalling 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 B

1) MSU (DPC = B)

3) UPU

2) Unable to deliver message,subsystem faulty

UPU User part unavailable message

Unavailabilitycause

User partId

2

00 DestinationH1

0001

H0

0100 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, andinhibited. If the link state is either available of inhibited, MTP level 3traffic 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

Link deactivation


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Emergency restart, an initial alignment for links of linkset that hasno 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 isinitiated

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 stepsinvolved are:

Checks database to find out if a destination may becomeunavailable as a result

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

The remote end sends an LSSU (LIA) as an acknowledgement toinhibit the link. If LIA is not received within a time limit, LIN may beresent. 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 uninhibitby LUN message. A remote destination point may force uninhibit bysending an LFU message. If the link has not been inhibited through theremote signalling point, it may recover the link by performing achangeback 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, anLSSU (SLTA) is received within 10 seconds and has the same testpattern. 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 signallingnetwork 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 theuser part of the destination address is not available. Depending on theunavailable user part (TUP and ISUP) the telephone traffic andsignalling 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 OUTOF SERVICE, or its initial alignment attempt has failed. If this signallinglink is the only one in the signalling link set, the system sets also alarm

2070, LINK SET UNAVAILABLE. If there is an alternative signalling linkavailable in the link set, the system performs a changeover. In this casethe signal transmission capacity is also decreased.

1548 MTP confusion message received

An MTP confusion message has been received in the exchange. Thesignalling point indicated by the originating point code given in the 3rdsupplementary information field has not identified the signalling networkmanagement message. The heading code of the signalling networkmanagement message is given in the 6th supplementary informationfield.

2064 Route set unavailable

The signalling point cannot be reached because none of the signallingroutes of the signalling route set can be used. Signalling traffic to thesignalling point concerned is totally blocked. This might cause a situationwhere CCS calls to the signalling point concerned fail or where, in theworst case, all outgoing calls, for example, fail (the signalling point thatcannot be reached is HLR) or all calls of a certain type fail (the signallingpoint that cannot be reached is for example SCP or SMSC).


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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 andthe signalling link is not brought into use. The system restarts thesignalling link and the signalling link test is repeated.

2070 Link set unavailable

All signalling links in the signalling link set are unavailable. There is nodirect connection to the partner exchange to which this link set isconnected. 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 partnerexchange or another exchange reached through this signalling link set.There is something wrong with the data transmission connections of thelinks of this link set, and/or links have been blocked. The exchangeautomatically attempts to re-establish the connection by attempting torestart the links that are in state UA-INS. The alarm 1072 SIGNALLINGLINK 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 otheravailable 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 hasalso 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 byusing various parameters. The parameters can be divided into thefollowing 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 Partof the signalling system

NMI

Signalling networkparameters

Whole signalling network NMO

Signalling link parametersets

Signalling links NOI

Signalling route setparameter sets

Signalling routes NNI

You can modify the functions of the MTP in the Common ChannelSignalling (CCS) system to a certain extent by modifying the relatedparameter values. The parameter values are stored in the parameterfiles, 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 ofthe parameter values are related to monitoring the functions, whileothers define various limits. In addition, a parameter can have differentvalues depending on the system and release level.

You can handle the level 3 parameters by using the commands NMI andNMM. The command NMI displays the used parameter values grouped by

the parameter sets. The command NMM is used to modify the usedparameters.

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 parameterwe want to modify and give the new value. Error: Reference source not

found lists the parameter groups, parameters and their indexes,parameter names and their meanings, the possible values of eachparameter and the value range, as well as the recommended value, ifthat exists.


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Table 5. Layer 3 parameters

Parameter Parameter

name/meaning

Value

A CSS7 COMMONPARAMETERS

A0-A9 DISTRIB_MTP_UNIT_TYPE_0 - 9 Defines those unittypes on an exchangewhere you can createsignalling links. Note:Usually, the parametervalues need not bechanged in the MSC, HLR,BSC or fixed networkexchanges, because unit

types CCSU, BCSU andBSU have been installed.

B OVERLOAD CONTROLPARAMETERS

B0 MAX_NB_OF_NOTICESThe largest amount ofincoming messagesallowed to enter acentralised unit during amessage-monitoring period(100 ms). Purpose of theparameter is to controloverload within the

exchange. The parametervalue should not bechanged.

10...30

C TIMER PARAMETERSFOR OWN SIGNALLINGPOINT

C0 LINK_TEST_PERIOD 1500...45000 (10 ms)

The sending period forsignalling link test messages.The period applies to a groupof 10signalling links. Thismeans that when an exchangehas 30 links, the test message

goes to each link in every thirdsending period.

4000 (40 sec.)

C1 Q704_T18_LINK_AVAIL_WAIT

1000... 6000 (10 ms)

The time used controlling theavailability of the links when asignalling transfer point isrestarted. The value dependson the implementation and onthe network.

2000

C2 Q704_T19_TRA_WAIT 200... 1000 (10 ms)


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Parameter Parameter name/meaning

Value

The timer controlling thereception of all TRA messageswhile the signalling transferpoint is being restarted, whenthe restarting is made asdefined in the CCITT BlueBook. The timer is defined byparameter P7 when the systemfollows the White Book.

400

C3 Q704_T20_TRAF_RESTARTING_TIME

200... 1000 (10 ms)

The timer controlling thesending of all TRA messageswhen the signalling transferpoint is being restarted.

400

C4 T111_T26 1000... 2000 (10 ms)

Defines the timer for resendingof TRW messages when thesignalling transfer point isbeing restarted, the timer isdefined in the ANSI standards.

1500

C5 Q714_T_GUARD 600... 9600 (100 ms)

Defines the monitoring timeused for the signallingconnections when thesignalling transfer point isbeing restarted.

6000

C6 T111_T27 300... 500 (10 ms)

After commencing the restartprocedure of a signalling point,all the signalling links of theexchange keep sending theprocessor outage stateindicator to the partnerexchanges for a given time(defined in this parameter).This is to make sure that alladjacent signalling pointsrecognise that this point cannotbe reached any more.

D PARAMETERS FORTESTING

D0 L2_TEST_MSG_SIO 0 ... FF

The service information octetused by the CCS System TestMessage Generator(MSGGEN) reads the dataonly when it starts up. Afterchanging the parametervalues, the MSGGEN has tobe restarted before new valuescan be included in the contentsof 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 partin the MSGGEN messagesof the CCS System TestMessage Generator. Thisparameter effects onlythose messages whoselength can be modified.Value for this parametercan be changed while theMSGGEN is running, andthe MSGGEN needs not berestarted.

smaller than 272

E INTERNAL ROUTINGPARAMETERS

E0 INT_ST7_ROUTE

Defines the number of theinternal routes that includethe PCM time slots used bythe signalling link terminalsbetween the unit and theswitching network.

E1 EXT_ST7_ROUTE

Defines the number of theexternal routes that include

the external PCM timeslotsused by the signalling linkterminals.

E2 INT_ST7_ROUTE_NAME

Defines the name of theinternal route that includesthe PCM timeslots used bythe signalling link terminalsbetween the unit and theswitching network.

E3 EXT_ST7_ROUTE_NAME

Defines the name of the

external route that includesthe external PCM timeslotsused by the signalling linkterminals.

E4 INTERNAL_ROUTING_FOR_SL

Defines whether thesystem tries to update thesignalling link relatedPCM/TSL data into the


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Value

routing data of theCM3PRO. Used only ontest exchanges that haveno group switch (GSW).

F CSS7 STATISTICSPARAMETERS

F0 SUCC_UNIT_COLL_COUNT_5

2... 10

Defines the number of MTPdecentralised units fromwhich the statisticscounters are collectedduring a 5-minute

monitoring period.

4

F1 SUCC_UNIT_COLL_COUNT_30

2... 20

Defines the number of MTPdecentralised units fromwhich the statisticscounters are collected oneby one during a 30-minutemonitoring period.

10

F2 SL_LOG_TYPE CYCLIC

Type of signalling link eventlog, which can be eitherNORMAL or CYCLIC.When the event log isstored in the normal buffer,the buffer can be emptiedwith command OLE.

CYCLIC

F3 SP_LOG_TYPE CYCLIC

Type of the signalling pointevent log, which can beeither NORMAL orCYCLIC. When the eventlog is stored in the normalbuffer, the buffer can beemptied with command

ONE.

CYCLIC

F4 SL_LOG_MAX_COUNT 16... 32

The maximum amount ofchanges in the state of asignalling link that can bestored in the buffer.

16

F5 SP_LOG_MAX_COUNT 16... 32

The maximum amount ofchanges in the state of a

16


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Value

signalling point that can bestored in the buffer.

F6 USER_NOTICE_ACT ACTIVE, PASSIVE

Controls the notices for theusers statistics output.

F7 SCCP_LOG_TYPE CYCLIC

Type of the SCCP eventlog buffer. ZOTE to clearthe buffer.

F8 TC_LOG_TYPE CYCLIC

Type of the TC event logbuffer. ZOTE to clear thebuffer

6.2 CCS7 signalling network-specific parameters

These parameters apply to the whole signalling network. All parametersthat are used specifically in the CSS7 signalling network are listed in this

section. There are also short descriptions on their meanings. Parametervalues vary depending on the system used and the release level.

The CSS7 signalling network-specific parameters are managed by usingthe commands NMO and NMC. The command NMO outputs the used

parameter values in each parameter set. The command NMC is used tomodify the used parameters.

The first parameter in the command defines the parameter set (J-M) ofthe 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 wantto modify and its new value. Table 6 lists the parameter groups,parameters and their indexes, parameter names and their meanings, allpossible values, and quality of parameter value and the recommendedvalue, if any.


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Table 6. CCS7 signalling network-specific parameters


Value

J NETWORK SPECIFICPARAMETERS

J0 CONGESTION_METHOD NO, INT, NAT, NATP

Three congestion methodsexist: international method(INT), national methodwithout prioritisation ofsignalling messages (NAT)and national method withprioritisation of messages(NATP).

INT method: Thecongestion criteria is thefilling degree (1 limit) of thesending buffer whose limitvalues are defined in theSignalling Link ParameterFile (SLNPAR). Thecongestion level directlyfollows the occupancy ofthe buffer. Timers T29 andT30 are used to control

traffic restriction accordingto definitions made withparameters K0-K5.

NAT method: Thecongestion criteria is thefilling degree (1 limit) of thesending buffer whose limitvalues are defined in theSignalling Link ParameterFile (SLNPAR). Timers Txand Ty determine thecongestion level. Thecongestion level can havevalues 1-3, and traffic is

restricted as required bythe prevailing congestionlevel and as defined inparameters L1-L3.

NATP method: Thecongestion criteria is theoccupancy (3 limits) of thesending buffer whose limitvalues are defined in theSignalling Link ParameterFile (SLNPAR). The


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Value

congestion leveldetermines how themessages are handled (forexample, on congestionlevel 3, only messages withpriority 3 or higher arerouted forwards).

K INTERNATIONALCONGESTION CONTROLMETHOD PARAMETERS

K0 NB_OF_UP_LEVELS 1 ... 5

The amount of restrictionlevels for the originating

traffic concerning the INTmethod.

K1 RESTRICT_PR_OF_UP_L1

0 ... 40 %

The restriction percentagefor the originating traffic onrestriction level 1. TimersT29 and T30 determine therestriction level. The defaultvalue is 40%.


20 ... 60 %



40 ... 80 %

The restriction percentagefor the originating traffic onrestriction level 3. TimersT29 and T30 determine therestriction level. The default

value is 70%.


60 ... 90 %



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Value


80 ...100 %


K6 Q764_T29 30 ... 60

When the first congestionindication is received by theISDN User Part (ISUP), thetraffic load into the affected

destination point code isreduced by one step. At thesame time timers T29 andT30 are started. During T29all received congestionindications for the samedestination point code areignored in order to notreduce traffic too rapidly.Reception of a congestionindication after the expiry ofT29, but still during T30,will decrease the trafficload by one more step and

restart T29 and T30. Thisstep-by-step reduction ofthe ISUP signalling traffic iscontinued until maximumreduction is obtained byarriving at the last step. IfT30 expires (for example,no congestion indicationsare no more receivedduring the T30 period)traffic will be increasedstep-by-step and T30 willbe restarted unless fulltraffic load has beenresumed.

50

K7 Q764_T30 500 ... 1000

See K6. 600

L NATIONAL CONGESTIONCONTROL METHODPARAMETERS

L0 PREDETERMINED_CONG_LEVEL

1 ... 3

Defines the default value


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Value

for the congestion level thatis reached when the bufferoccupancy limit isexceeded for the first time,or when the congestionlevel is coded as 0 in areceived TFC message.

L1 RESTRICT_PR_OF_MTP_ L1

0 ... 50 %

The restriction percentagefor originating traffic oncongestion level 1.

L2 RESTRICT_PR_OF_MTP_

L2

20 ... 80 %


L3 RESTRICT_PR_OF_MTP_ L3

50 ...100 %


L4 Q704_TX 5 ... 200

The timer raises the

congestion level when thefilling limit of the transmitbuffer has been exceeded.The smaller the parametervalue is, the faster thecongestion level is raised.(If the signalling linkcongestion status is set to sand the buffer occupancycontinues to be above theset congestion thresholdduring Tx, the signallinglink congestion status isupdated by the new value s+ 1.)

200 ms

L5 Q704_TY 5 ... 200

The timer lowers thecongestion level whencongestion has been on butthen the filling degree ofthe sending buffer isdecreased and goes belowthe set limit. The smallerthe Ty is, the faster thecongestion level


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Value

decreases. (If the signallinglink congestion status is setto s and the bufferoccupancy continues to bebelow the abatementthreshold during Ty, thesignalling link congestionstatus is updated by thenew value s - 1.)

M SLS BITS

M0 LINK_SLS_BIT_MASK

Defines which SLS bits areused in load sharing within

the link set.

ITU: 00001111 ANSI:

11111110

M1 ROUTE_SLS_BIT_MASK

Defines which SLS bits areused in load sharingbetween the routes.

ITU: 00001111 ANSI:

00000001

M2 SLS_LENGTH 4,5,8

Defines the length of SLSwithin the signallingnetwork. In ITU networks,the SLS is 4 bits, while inANSI networks it is 5 or 8bits. ITU: 4 ANSI: 5 or 8.

6.3 Signalling link specific parameters

The parameters in the signalling link specific parameter set define howthe signalling links function. All signalling link-specific parameters arelisted 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 thecommands in the command group NO. The commands can be used to

modify existing parameter sets or to create new ones. Before you startmodifying an existing parameter set, check that all signalling links usingthis parameter set have been deactivated. The new values becomeeffective when the links are activated again. To create a new parameterset, you can replicate (copy and rename) an old parameter set andmodify 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 theparameter values in an existing parameter set.

In the command, the name and number of the parameter set aredefined. In addition, the identifier of the parameter group is definedaccording 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 (asdefined 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 fromthe parameter set you want to modify, and gives the new value. Table 7lists the parameter groups, parameters and their indexes, parameternames and their meanings, all possible values, quality of the value andthe recommended value, if any

Table 7. Signalling link specific parameters


Value

A MISCELLANEOUS MTPLEVEL 2 PARAMETERS

A0 LI_CODING STANDARD, BTNR

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

STANDARD

A1 BIT_D_CODING_IN_LSSU STANDARD, BTNR

Controlling the D bit codingin the LSSUs. BTNR is aspecific method in BTNRSpec. (UK).

STANDARD

A2 BIT_D_CHECK_IN_LSSU YES, NO

Controlling the D bitchecking in the receivedLSSUs. (1H Bit D checkedfrom the received LSSU).

YES

A3 L2_ERROR_CORRECTIO BASIC, PCR


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Value

N

Controlling the error ratemonitoring in thetransmission direction.PCR is for preventive cyclicretransmission for satellitelinks.

BASIC

A4 SN_RANGE 404095

Maximum value forbackward sequencenumber and forwardsequence number ofsignalling unit.

127

A5 JT_Q703_K 40127

Defines the number oftransmitted MSU messageswithout positiveacknowledgement. Thisparameter is relevant onlyin Japanese signallingnetwork.

40

B MTP LEVEL 2 ERRORRATE MONITORINGPARAMETERS

B0 SUERM_T 8 ... 512

Controlling the error rate ofthe message unit:SUERM_T, SUERM_D andSUERM_N (see CCITTQ703 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 4


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Value

the alignment AERM_TIN,(see CCITT Q703 10.3).

B4 AERM_TIE 1 ... 8

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

1

B5 AERM_M 1 ... 16

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

5

B6 AERM_N 8 ... 24

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

16

B7 PCR_N1 (preventive cyclicretransmission)

1 ... 127

PCR_N1, number of MSUsthat can be resent.

127

B8 PCR_N2 300 ... 6000

PCR_N2, number of MSUsthat can be resent.

800

B9 EIM_TE 8 ... 793544

Error interval monitorparameter (see ITU-TQ703 A.10.2)

99193

B10 EIM_UE 1 ... 198384

Error interval monitorparameter (see ITU-TQ703 A.10.2)

24798

B11 EIM_DE 1 ... 11328

Error interval monitor

parameter (see ITU-TQ703 A.10.2)

1416

B12 JT_Q703_TE 20 ... 30 (1 ms)

Defines the normalizedtime for error ratemonitoring. This parameteris relevant only inJapanese signallingnetwork.

24


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Value

C MTP LEVEL 2 TIMERPARAMETERS

C0 Q703_T1 130 ... 500 (0.1s)

Q703_T1, AlignmentCompleted timer.

400

C1 Q703_T2 50 ... 1500 (0.1s)

Q703_T2, No Alignementtimer.

100

C2 Q703_T3 10 ... 116 (0.1s)

Q703_T3, Alignment timer. 10

C3 Q703_T4 23 ... 95 (0.1s)Q703_T4, Length of TestPeriod timer.

82

C4 Q703_T5 8 ... 30 (0.1s)

Q703_T5, SIBTransmission timer.

10

C5 Q703_T6 30 ... 72 (0.1s)

Q703_T6, Remote EndCongestion timer.

50

C6 Q703_T7 5 ... 20 (0.1s)

Q703_T7, DelayedAcknowledgement 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 sendingFISU when there is noMSUs transmitted. Thisparameter is relevant onlyin Japanese signallingnetwork.

24

C9 JT_Q703_TO 20 ... 30 (1 ms)

Defines interval fortransmitting SIO and SIEmessages used for initialset-up and duringverification. This parameteris relevant only inJapanese signallingnetwork.

24


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Value

C10 JT_Q703_TS 10 ... 30 (1 ms)

Defines interval of SIOS tobe transmitted duringsuspension. Thisparameter is relevant onlyin Japanese signallingnetwork.

24

D MISCELLANEOUS MTPLEVEL 3 PARAMETERS

D0 PERIODIC_LINK_TEST_DENIED

YES, NO

Controlling thetransmission of signallinglink test messages.

NO

D1 MAX_LENGTH_OF_SIF 272

Maximum length of the SIFfield in the MSU message.

272

D2 INHIBIT_ATTEMPT_LIMIT 1 ... 5

Limit for repeated attemptsto 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 ofEmergency Changeoverprocedure.

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 SIGNALLINGCONGESTION CONTROLPARAMETERS

E0 CONG_FILTERING_TIME 10 ... 100 (0.01s)

Defines the time afterwhich continuingcongestion on a signallinglink is reported to level 3.This feature keeps thesignalling traffic control

procedures from startingduring very short-time peakloads. 30 (0.3s).

1

E1 BUFF_FILTERING_TIME 50 ... 300 (0.01s)

Defines the time afterwhich continuingcongestion on a signallinglink is reported to level 3while signalling messagebuffering is active. Thisfeature keeps the signallingtraffic control proceduresfrom starting in special

situations such aschangeovers, changeback,and controlled rerouting.150 (1,5s).

1

E2 CONG_ONSET_THRESHOLD1

2 ... 1000

Reports the occupancy ofthe transmission buffer thatis interpreted as level 1congestion. Congestioncan be set for thresholdvalues 0-127; if the value is128-255, signalling link

congestion is never on. Thelimit for congestion onset(messages) is 49.

49

E3 CONG_ABATE_THRESHOLD1

1 ... 800

Reports the occupancy ofthe transmission buffer thatis interpreted as ending forlevel 1 congestion (that hasbeen on). It is advisable toset the release level of

2


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Value

congestion lower than theactivation level to avoidvibrations. The limit forcongestion reset(messages) is 2.

E4 CONG_DISC_THRESHOLD1

0 ... 2500, NOT IN USE

Reports the occupancy ofthe transmission buffer thatenables the signallingterminal software to set thesignalling message. Thissets the destroy status inthe transmission mailbox.When the CCSENDprogram block notices thatthe destroy status is set, itdestroys the signallingmessages addressed to thementioned signallingterminal. The thresholdvalues for the destroystatus are selected fromthe range 0-127; if thevalue is 128-255, the statusis not set. However, whenthe transmission buffer fillsup, signalling messages

have to be destroyed. Thestatus value must thereforebe higher than the limit forsignalling link congestion inorder to avoid unnecessarymessage destruction. Thelimit for messagediscarding (messages) isNOT IN USE.


2 ... 1000, NOT IN USE

CONG_ONSET_THRESHOLD2,CONG_ABATE_TH

RESHOLD2,CONG_DISC_THRESHOLD2,CONG_ONSET_THRESHOLD3,CONG_ABATE_THRESHOLD3andCONG_DISC_THRESHOLD3 are similar to the above-mentioned parameterswhen the congestioncontrol method that is usedhas several levels. Theparameter values on level 2


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Value

must be higher than thecorresponding values onlevel 1, and values on level3 must be higher thanthose on level 2 in order toget the congestion methodto work properly. When thecongestion method usesonly one level, set theparameter values on levels2 and 3 as 255 = 0FFH.See parameters E2, E3.

E4 & E6 CONG_ABATE_THRESHOLD2

1 ... 800, NOT IN USE Seeparameters E5 and E3

E7 CONG_DISC_THRESHOLD2

10 ... 2500, NOT IN USESee parameters E5 and E4



E9 CONG_ABATE_THRESHOLD3

1 ... 800, NOT IN USE Seeparameters E5 and E3

E10 ONG_DISC_THRESHOLD3


E11 T111_T31_ONSET_THRESHOLD

1, 2, 3, NOT IN USE

Congestion threshold forstarting timer T111_T31.

0

E12 T111_T31_RESET_THRESHOLD

1, 2, 3, NOT IN USE

Congestion threshold forresetting timer T111_T31.

0

E13 SL_LOAD_THRESHOLD 100 ... 900

Allows maximum value forsignalling link load inMerlangs withoutnotification.

200

F MTP LEVEL 3 TIMINGPARAMETERS

F0 Q704_T1 5 ... 12 (0.1s)

Delay to avoid messagemis-sequencing onchangeover.

8

F1 Q704_T2 7 ... 20 (0.1s)

Waiting for changeoveracknowledgement.

14


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Value

F2 Q704_T3 7 ... 12 (0.1s)

Time controlled diversion-delay to avoid mis-sequencing onchangeback.

8

F3 Q704_T4 5 ... 12 (0.1s)

Waiting for changebackacknowledgement (firstattempt).

8

F4 Q704_T5 5 ... 12 (0.1s)

Waiting for changebackacknowledgement (secondattempt).

8

F5 Q704_T12 8 ... 12 (0.1s)

Waiting for un-inhibitionacknowledgement.

10

F6 Q704_T13 6 ... 15 (0.1s)

Waiting for force un-inhibitionacknowledgement.

10

F7 Q704_T14 8 ... 30 (0.1s)

Waiting for inhibition

acknowledgement.

20

F8 Q704_T17 8 ... 60 (0.1s)

Delay to avoid oscillation ofinitial alignment failure andlink 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 linktest messageacknowledgement.

80

F12 T111_T19 120 ... 600 (1s)

Time supervision for settingan alarm about a signallinglink that refuses to start up,as defined in ANSIstandards.

120


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Value

F13 T111_T20 90 ... 120 (1s)

Control for local inhibitiontesting as defined in ANSIstandards.

120

F14 T111_T21 90 ... 120 (1s)

Control for remote endinhibition testing as definedin ANSI standards.

120

F15 T111_T31 10 ... 120 (1s)

False link congestiondetection 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 fortransmitting SIOS on aperiodical basis duringsuspension. Thisparameter is relevant onlyin Japanese signallingnetwork.

30

F18 JT_Q707_T10 0..600 (0.1s)

This parameter is relevantonly in Japanese signallingnetwork.

100

F19 ALIGN_RESPONSE_WAIT 40

6.4 Signalling route set specific parameters

The parameters included in the parameter set of the signalling route setare used to handle the functions of the whole Message Transfer Part(MTP). This section introduces all parameters that are specific to eachsignalling route set and describes their purposes briefly. The parametervalues va

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MTP Document