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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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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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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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
Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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%.
K2 RESTRICT_PR_OF_UP_L2
20 ... 60 %
The restriction percentagefor the originating traffic onrestriction level 2. TimersT29 and T30 determine therestriction level. The defaultvalue is 60%.
K3 RESTRICT_PR_OF_UP_L3
40 ... 80 %
The restriction percentagefor the originating traffic onrestriction level 3. TimersT29 and T30 determine therestriction level. The default
value is 70%.
K4 RESTRICT_PR_OF_UP_L4
60 ... 90 %
The restriction percentagefor the originating traffic onrestriction level 4. TimersT29 and T30 determine therestriction level. The defaultvalue is 80%.
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Parameter Parameter name/meaning
Value
K5 RESTRICT_PR_OF_UP_L5
80 ...100 %
The restriction percentagefor the originating traffic onrestriction level 5. TimersT29 and T30 determine therestriction level. The defaultvalue is 90%.
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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Parameter Parameter name/meaning
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 %
The restriction percentagefor originating traffic oncongestion level 2.
L3 RESTRICT_PR_OF_MTP_ L3
50 ...100 %
The restriction percentagefor originating traffic oncongestion level 3.
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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Parameter Parameter name/meaning
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
Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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
Controlling the error rate ofthe message unit:SUERM_T, SUERM_D andSUERM_N (see CCITTQ703 10.2).
256
B2 SUERM_N 8 ... 24
Controlling the error rate ofthe message unit:SUERM_T, SUERM_D andSUERM_N (see CCITTQ703 10.2).
16
B3 AERM_TIN 1 ... 16
Controlling the error rate of 4
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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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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Parameter Parameter name/meaning
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.
E5 CONG_ONSET_THRESHOLD2
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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Parameter Parameter name/meaning
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
E8 CONG_ONSET_THRESHOLD3
2 ... 1000, NOT IN USESee parameters E5 and E2
E9 CONG_ABATE_THRESHOLD3
1 ... 800, NOT IN USE Seeparameters E5 and E3
E10 ONG_DISC_THRESHOLD3
10 ... 2500, NOT IN USESee parameters E5 and E4
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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Parameter Parameter name/meaning
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