63406761-MSC-SCCP-1

Signaling Connection Control Part (SCCP)

Chapter 3

This chapter is designed to provide the student with a basicknowledge of SCCP.

OBJECTIVES:Upon completion of this chapter the student will be able to:

• Explain the sequence for a signaling message in SCCP

• Use MML printout commands to obtain a view of the SCCPconfiguration and use the B-module to interpret the results

• Define a SCCP network using the B-module and a workorder

GSM MSC/VLR Operation

EN/LZT 123 3976 R6A

ll aa nn kkBB

iioonnaall llyy

ttnneettnnII

3 Signaling Connection Control Part (SCCP)

EN/LZT 123 3976 R6A – i –

3 Signaling Connection Control Part(SCCP)

Table of Contents

Topic Page

INTRODUCTION..................................................................................41

SCCP ADDRESSING...........................................................................43

GLOBAL TITLE (GT) ................................................................................................... 44

EXAMPLE ............................................................................................47

PREREQUISITES........................................................................................................ 47

ANALOGY BETWEEN CALLS AND S7 MESSAGES ................................................. 47

CALLING AND CALLED ADDRESS............................................................................ 48

GLOBAL TITLE TRANSLATION.................................................................................. 51

GLOBAL TITLE ROUTING .......................................................................................... 53

STAND-ALONE HOME LOCATION REGISTER (HLR) ......................55

SCCP ROUTING IN GSM 1900 ...........................................................56

MAJOR PRINTOUTS IN S7.................................................................60


– ii – EN/LZT 123 3976 R6A

ll aa nn kkBB

iioonnaall llyy

ttnneettnnII


EN/LZT 123 3976 R6A – 41 –

INTRODUCTION

The S7 consists of various functional elements where theMessage Transfer Part (MTP) is the common platform. MTPserves different user parts, such as Telephony User Part (TUP),Integrated Services Digital Network User Part (ISUP), and otherfunctional elements like Signaling Connection Control Part(SCCP).

SCCP provides additional functionality to fulfill the need forextended services in certain applications.

An example of an extended service is communication with thedatabases, Home Location Register (HLR) and Visitor LocationRegister (VLR), without any speech connection, e.g.communication during Location Updating.

The combination of the MTP and the SCCP is called theNetwork Service Part (NSP).

SCCP supports two network services:

• Connection Oriented (CO)

• ConnectionLess (CL)

See Figure 3-1.

The CO transfers many or long signaling messages between twonodes. In this case, it makes sense to “establish a logicalconnection” between the sender and receiver.

The CL transfers short messages, including routing information,to their destination.


– 42 – EN/LZT 123 3976 R6A

MTP

SCCPCL CO

TCAP

MAP

BSSAP ISUP

CO = Connection-OrientedCL = Connection-Less

Figure 3-1 SCCP and other protocols

The protocol between the Mobile services SwitchingCenter/Visitor Location Register (MSC/VLR) and the BaseStation Controller (BSC) is called Base Station SystemApplication Part (BSSAP).

BSSAP requires both the Connection Oriented (CO) and theConnectionLess (CL) service. The MSC/VLR, HLR, and GMSCcommunicate via the Mobile Application Part (MAP), usingonly the ConnectionLess (CL) mode. The TransactionCapabilities Application Part (TCAP) supports MAP. However,there is no need to describe TCAP functionality to understandhow GSM works.

Note: BSSAP and TCAP are not explained here.

While SCCP performs tasks similar to MTP; e.g. routing, SCCPallows only routing of MAP/BSSAP messages MTP and SCCPshould be considered as two different networks that are linkedtogether.


EN/LZT 123 3976 R6A – 43 –

SCCP ADDRESSING

SCCP enables an S7 to route MAP messages. Routing is alwaysbased on addresses. SCCP uses the following addresses:

• Calling address — identifies call origination

• Called address — identifies call destination

SCCP addressing is very flexible and makes use of threeseparate elements:

• Destination Point Code (DPC)

• Global Title (GT)

• SubSystem Numbers (SSN)

See Figure 3-2.

Routinglabel

Callingaddress

Calledaddress

OPC DPC

SSN

TTNPNAAI

MTP SCCP TCAP MAP

Global title

SSN = SCCP Subsystem NumberTT = Translation TableNP = Numbering Plan

NA = Nature of AddressAI = Address Information

Figure 3-2 SCCP addressing


– 44 – EN/LZT 123 3976 R6A

One, two, or three elements may be present in the addressinformation for the called and the calling party. The form of theaddress depends on the service, application, and underlyingnetwork. The Address Indicator shows which informationelements are present.

GLOBAL TITLE (GT)

The GT is of variable length, and can contain specifiedcombinations of:

• Address Information (AI)

• Nature of Address (NA)

• Numbering Plan (NP)

• Translation Type (TT)

(see ITU, Q. 71x series)

It does not contain information that allows routing in thesignaling network. The translation function is required.

The following sections contain details and typical values forsome of the elements previously listed:

SubSystem Number (SSN)

The terminating node examines the SSN to identify theconcerned user (node).

6 HLR

7 VLR

8 GMSC, MSC

9 EIR

10 AUC

12 SC

222 BSC (BSSAP) in case of ANSIsignaling (GSM 1900)

224 HLR-R (HLR Redundancy)

254 BSC (BSSAP) in case of CCITTsignaling (GSM 900)

3 ISUP (if ISUP uses SCCP)


EN/LZT 123 3976 R6A – 45 –

Address Information (AI)

This is an address according to the numbering plan indicated.(See the example in Numbering Plan).

Nature of Address (NA)

NA indicates if the address is

3 National

4 International

format according to the numbering plan used.

Numbering Plan (NP)

NP indicates the numbering scheme from which the addressoriginates:

1 ISDN/Telephony Numbering Plan (E.163/E.164)

e.g. MSISDN, GT address

7 ISDN/Mobile Numbering Plan (E.214)

e.g. IMSI, MGT (Location Updating)

Translation Type (TT)

A GT requires a translation function. The TT directs themessage to the appropriate Global Title (GT) translation.

It is possible for the Address Information (AI) to be translatedinto different values for different combinations of DPCs, SSNsand GTs.


– 46 – EN/LZT 123 3976 R6A

0 CCITT signaling

9 ANSI signaling

1-8, Used for the Service Center (SC) interface

10-254 MTS exchange property SMSFMOSMTRTYPE

EXAMPLE� NA=4, NP=1, AI=49 172, TT=0

NP indicates a normal ISDN/Telephony number. NA indicatesinternational format for AI. Therefore, 49 is the Country Code(CC) for Germany and 172 is the NDC for D2 operator, and theTranslation Type (TT) is CCITT signaling.


EN/LZT 123 3976 R6A – 47 –

EXAMPLE

This example describes SCCP from an Operation stand point. Itis based on the network illustrated in Figure 3-3, and exchangedata printouts shown on the following pages. It is the samenetwork used in the example in Chapter 2 MTP.

The example focuses on basic S7 exchange data. S7 supervisiondata is not presented here.

Note: The printouts are exclusively made in the switching nodeDüsseldorf.

Düsseldorf

Hamburg

Berlin

BSC

BSC

BSC

Othernetwork

PLMN

Traffic

Signaling

IntegratedMSC/VLR,GMSC, HLR

BSC

Figure 3-3 Example

PREREQUISITES

SCCP runs on top of MTP. The MTP network must beoperational before SCCP can be started.

ANALOGY BETWEEN CALLS AND S7 MESSAGES

Figure 3-4 illustrates a similarity between the “sequence” ofhandling a call and an S7 message (MTP, SCCP).

Note: It is assumed that the reader knows the sequence forhandling a call and for handling an MTP message.


– 48 – EN/LZT 123 3976 R6A

CALL:

A - No (SENDER-ID)

B - No (RECEIVER-ID)

RC ROUTE DEVICESETC(HW)

TERMINATING

MTP

OWNSP

SP

DEST LS SLCSignalingTerminal(HW)

TERMINATING

SS No 7Message

SCCP

Calling Address

Called Address

GT GTRC DPC

TERMINATING

Passed toMTP!

Figure 3-4 Analogies in sequences

This figure is shown at an early stage in the example to providethe reader with an overview of SCCP.

SCCP runs on top of MTP and only the MTP network hasaccess to the physical link, e.g. cable.

To send a MAP message between two different locations, theMTP sequence must be passed after the SCCP sequence.

CALLING AND CALLED ADDRESS

Different elements, e.g., DPC, SSN, may be present in thecalling and called address.


EN/LZT 123 3976 R6A – 49 –

Hamburg

Berlin

BSC

BSC

BSC

Othernetwork

PLMN

Traffic

Signaling


BSC Düsseldorf Own calling addressHLRINT = 49 172 21 00096HLPNAT = 172 21 00096MSCINT = 49 172 21 00097MSCNAT = 172 21 00097

SP=2-6025SSN=254

SP=2-6050SSN=6&7&8

SP=2-6113SSN=6&7&8

Figure 3-5 Calling and called address

Each node must have its individual calling address, used innational and international transmission. It has the same structure(defined by E.164) as an MSISDN. The structure isCC+NDC+SN.

See Figure 3-5 and Figure 3-6.

In the individual node address, CC and NDC (NPA in GSM1900) are pre-determined; the SN is up to the network operator.The individual node address for the HLR and theMSC/VLR/GMSC may be different, e.g. the HLR(Düsseldorf)address is 49 172 2100096, while the MSC/VLR/GMSC addressis 49 172 2100097.


– 50 – EN/LZT 123 3976 R6A

<HGCAP;HLR OWN CALLING ADDRESS DATA

INT NAT491722100096 1722100096END

<MGCAP;MT OWN CALLING ADDRESS DATA

INT NAT491722100097 1722100097END

<C7NCP:SP=ALL,SSN=ALL;CCITT7 SCCP NETWORK CONFIGURATION DATA

SP SPID SP STATE BROADCAST STATUS2-6025 DUDFBSC ALLOWED NCON

SSN SUBSYSTEM STATE 254 ALLOWED

SP SPID SP STATE BROADCAST STATUS2-6050 HAMBURG ALLOWED CON

SSN SUBSYSTEM STATE 6 ALLOWED 7 ALLOWED 8 ALLOWED

SP SPID SP STATE BROADCAST STATUS2-6113 BERLIN ALLOWED CON

SSN SUBSYSTEM STATE 6 ALLOWED 7 ALLOWED 8 ALLOWED

END

Figure 3-6 Printout of own calling address and cooperating SPs

Each node has a list of all potential called addresses, cooperatingSignal Points (SPs), in a network. A destination is identified byits Signaling Point Code (SPC), see Figure 3-6.

Each node knows the SSNs for its subsystems. However, theSSNs available in the cooperating SPs must be defined.

When signaling traffic is permitted in a subsystem, via SCCP,its state is set to ALLOWED.

In the example, node Düsseldorf has SSN=254 (BSC) availableat SP=2-6025 (DUDFBSC). The cooperating SPs HAMBURG(2-6050) and BERLIN (2-6113) have integrated the HLRs(SSN=6), VLRs (SSN=7) and the MSC/GSMCs (SSN=8).


EN/LZT 123 3976 R6A – 51 –

OTHERNT (0-1111) and its SSN are unknown to Düsseldorf;therefore, routing can only be performed in MTP.

GLOBAL TITLE TRANSLATION

A node either originates, terminates, or transfers a message.

To generate an originating labeled message, the node uses thecalling and called address. The form of the address depends onthe service, application, and underlying network.

The Routing Indicator (RI) determines the method ofterminating or transferring a message at a node. The form of theindicator depends on the service and application.

Due to these complex interrelations, it can be assumed that:

• HLR(Düsseldorf) serves subscribers having MSISDNs= 49172 21xxxxx.

• HLR(Hamburg) serves subscribers having MSISDNs= 49172 40xxxxx.

• HLR(Berlin) serves subscribers having MSISDNs= 49 17230xxxxx.

Figure 3-7 and Figure 3-8 illustrate the corresponding GlobalTitle (GT) translation for Düsseldorf.

Berlin

BSC

BSC

Othernetwork

PLMN

TrafficSignaling


BSC

Düsseldorf Own calling addressHLRINT = 49 172 21 00096HLPNAT = 172 21 00096MSCINT = 49 172 21 00097MSCNAT = 172 21 00097 SP=2-6025

SSN=254

SP=2-6050SSN=6&7&8

SP=2-6113SSN=6&7&8

NS NA NP TT DESUST... ... ... ... TERM... ... ... ... GTRC

Hamburg

GTRC=2

GTRC=1 49 172 30 ****

49 172 21 ****

49 172 40 ****

HLR

HLR

HLR BSC

Figure 3-7 Global Title (GT) translation in Düsseldorf


– 52 – EN/LZT 123 3976 R6A

In this part of the example:

1. GMSC(Düsseldorf) receives a call for MSISDN=49 1723011111.

2. GMSC(Düsseldorf) requests routing information from theHLR(Berlin), sending a MAP message via the SCCP andMTP network.

3. The first digits (NS=49 172 30) of the MSISDN(NA=4,NP=1) are used as the called address.

4. GMSC must transfer that message. Therefore the result ofthe translation is a Global Title Routing Case (GTRC=1).

<C7GSP:GTRC=ALL;CCITT7 GLOBAL TITLE SERIES TRANSLATION DATA

OPERATING

TT NP NA NS TRANSLATION RESULT0 1 3 17230 GTRC = 10 1 3 17240 GTRC = 2

0 1 4 4917230 GTRC = 10 1 4 4917240 GTRC = 2

0 7 4 4917230 GTRC = 10 7 4 4917240 GTRC = 2

END

0 1 3 17221 GTRC = 3

0 1 4 4917221 GTRC = 3

0 7 4 4917221 GTRC = 3

Figure 3-8 Printout of Global Title (GT) translation in Düsseldorf

Figure 3-4 illustrates the similarities between Global TitleRouting Case (GTRC) and Routing Case (RC). It is the input forthe Global Title (GT) routing.

However, in the case that the call is for MSISDN=49 172 2122222, GMSC must send a MAP message to the internal HLR.

No Global Title (GT) translation to the BSC (SSN=254) isperformed.

Note: In GSM 1900, when no translation is required — whenmessages are sent to an internal element such as the HLR —these messages are defined as forwarded to a Local SubSystem(LSS). See SCCP Routing in GSM 1900.


EN/LZT 123 3976 R6A – 53 –

GLOBAL TITLE ROUTING

The Global Title (GT) routing ties a destination, SP, to a GTRC(see Figure 3-4).

Example:

PSP=2-6113 is linked to GTRC=1 and is the Primary SignalingPoint (PSP). If the first choice becomes faulty, the specifiedSecondary Signaling Point (SSP=2-6050) is used as thealternative point.

Note: This is optional. Hamburg must support this alternative.

Berlin

BSC

BSC

Othernetwork

PLMN

Traffic

Signaling


BSC

Düsseldorf Own calling addressHLRINT = 49 172 21 00096HLPNAT = 172 21 00096MSCINT = 49 172 21 00097MSCNAT = 172 21 00097 SP=2-6025

SSN=254

SP=2-6050SSN=6&7&8

SP=2-6113SSN=6&7&8

NS NA NP TT DESUST... ... ... ... ... ... ... ... GTRC

Hamburg

GTRC=2

GTRC=1 49 172 30 ****

49 172 21 ****

49 172 40 ****

HLR

HLR

HLR BSC

PSP=2-6113PTERM=YESSSP=2-6050STERM=NO

PSP=2-6050PTERM=YESSSP=2-6113STERM=NO

Figure 3-9 Global Title (GT) routing with alternatives

The Global Title (GT) routing enables one node to decide howthe message must be handled in the next node.

Example:

A message sent with GTRC=1 to PSP=2-6113 must beterminated in the next node (Berlin). Therefore, PSP is markedas PTERM=YES in Düsseldorf.

Note: In GSM 1900, to indicate the message is terminated in thenext node, PSP is given a Routing Indicator (RI) of SubSystem(SS) and the PSP subsystem is named (PSSN). See SCCPRouting in GSM 1900.


– 54 – EN/LZT 123 3976 R6A

<C7GCP:GTRC=ALL;

CCITT7 GLOBAL TITLE ROUTING CASE DATA

GTRC PSP PTERM PINTER PSSN SSP STERM SINTER SSSN

1 2-6113 YES NO 2-6050 NO YES2 2-6050 YES NO 2-6113 NO YES

END

Figure 3-10 Printout of the global title routing

A message sent with GTRC=1 to Berlin via the alternativeHamburg (SSP=2-6050) must be transferred in Hamburg.Therefore, SSP is marked STERM=NO in Düsseldorf.Düsseldorf sets the Routing Indicator (RI) so that Hamburg mustperform a GT translation and GT routing.

The Routing State indicates which routing; Primary, Secondary,or Prohibited, is possible.

After a node has determined the destination (PSP, SSP) onSCCP, MTP uses the Signaling Point (SP) as input to find theappropriate physical link, e.g. cable. See Figure 3-4.


EN/LZT 123 3976 R6A – 55 –

STAND-ALONE HOME LOCATION REGISTER (HLR)

There are only minor differences between a stand-alone and anintegrated HLR.

Note: It is assumed here that the network has a single stand-alone HLR.

• None of the HLR cooperating Signaling Points (SPs) canhave SSN=6 (HLR)

• A cooperating SP of type “stand-alone HLR” has onlySSN=6 (HLR)


– 56 – EN/LZT 123 3976 R6A

SCCP ROUTING IN GSM 1900

SCCP routing in GSM 1900 networks is accomplishedessentially as described in the previous example. The majordifferences are that, in GSM 1900:

• Signaling Points (SPs) are specified as network-cluster-member numbers, e.g. 251-10-10, rather than as networkindicator-signaling point code numbers. See the chapterMTP.

• Element National Destination Code (NDC) in the MSISDNis called Numbering Plan Area (NPA). See GSM identitynumbers in the chapter “Introduction”.

• S7xxx commands are used. No C7xxx commands areapplicable. See the paragraph Major Printouts in S7 tofollow.

• Own-node termination of Global Title (GT) translation(S7TSI) is specified with the parameter LSS (localsubsystem), rather than with the parameter TERM. SeeFigure 3-11 through Figure 3-13.

• Global Title Routing Cases (GTRCs) (S7GCP) are specifiedwith a Routing Indicator (RI) of the Global Title (GT) or theSubSystem (SS). When SS is indicated, the SubSystemNumber (SSN) is given. See Figure 3-11 through Figure 3-13.

Figure 3-11, Figure 3-12, and Figure 3-13 to follow containexamples of GSM 1900 S7xxx printouts comparable to theGSM 900 C7xxx printouts shown in Figure 3-6, Figure 3-8, andFigure 3-10, respectively.


EN/LZT 123 3976 R6A – 57 –

Figure 3-11 Printout of own calling address and cooperatingSPs (GSM 1900)


– 58 – EN/LZT 123 3976 R6A

Figure 3-12 Printout of Global Title (GT) translation (GSM1900)


EN/LZT 123 3976 R6A – 59 –

Figure 3-13 Printouts of Global Title (GT) routing (GSM 1900)


– 60 – EN/LZT 123 3976 R6A

MAJOR PRINTOUTS IN S7

Table 3-1 shows an overview of the major S7 SCCP printoutcommands.

Note: This overview does NOT replace any official systemdocumentation, e.g. B-module.

&RPPDQG

�*60��

&RPPDQG

�*60��

'HVFULSWLRQ

2ZQFDOOLQJDGGUHVV

MGCAP MGCAP MSC/VLR/GMSCown

Calling address

HGCAP HGCAP HLR own

Calling address

6&&3QHWZRUNFRQILJXUD�

WLRQ

C7NCP:SP=sp,

SSN=all

S7NCP:SP=all Cooperating SP

+ subsystems

DATA,

STATE

*OREDOWLWOH�WUDQV�ODWLRQ

C7GSP:GTRC=

gtrc

S7TSP:GTS=all,

GTRC=all

Translation

Into GTRC

*OREDOWLWOHURXWLQJ

C7GCP:GTRC=

gtrc

RU

C7GCP:

GTRC=all,...

S7GCP:GTRC=

all

RU

S7GCP:GTRC=

all,RI=GT,SP=sp

RU

S7GCP:GTRC=

all,RI=SS,SP=sp,

SSN=ssn

Routing

GTRC --> SP

Table 3-1: Major printout commands - SCCP.

63406761-MSC-SCCP-1

Documents

Transcript of 63406761-MSC-SCCP-1