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The applications of present-day transactions fall into several groups: 380 Signaling in Telecommunication Networks... 13.2.1 Application Service Elements We say that a signaling point S

13’

INTRODUCTION TO TRANSACTIONS

The TUP and ISUP protocols (Chapters 9 and 11) are SS7 protocols for trunk- related exchange actions (mainly call control) The SS7 signaling takes place between the exchanges at the ends of a TUP or ISUP trunk

Starting with this chapter, the focus is on SS7 signaling for operations that are not trunk-related

13.1 DEFINITIONS AND APPLICATIONS

13.1 l Definitions

Remote Operation This is an operation that is not trunk-related, and is executed by one signaling point (SP), at the request of another SP

Transaction This is a dialogue consisting of signaling messages between two SPs, for the execution of one or more remote operations [l-3]

Transactions can involve two exchanges, an exchange and a network database, an exchange and a maintenance center, etc

13.1.2 Applications

Transactions are the successors of the direct signaling procedures of common- channel interoffice signaling (CCIS)-see Section 6.5 The applications of present-day transactions fall into several groups:

380

Signaling in Telecommunication Networks John G van Bosse

Copyright  1998 John Wiley & Sons, Inc ISBNs: 0-471-57377-9 (Hardback); 0-471-22415-4 (Electronic)

lntelliigent Network Services such as “800” and “900” calls (6.51) For these calls, an exchange needs to query a network database to obtain a routing number that corresponds to the received 800 or 900 number (6.5.1) Intelligent network (IN) services are discussed in Chapter 16

Services for Mobile Telecommunications [3] As one example, transactions are used to keep track of the present location of each active mobile station (MS) This information is used when routing a call to a MS Services for mobile telecommunications are described in Chapter 17

Centralized Operation, Administration, and Maintenance (OAM) of a telecommunication network, where an OAM center uses transactions to verify and change the data stored in exchanges, to request a test of network equipment, etc

Bulk Data Transfer, for example, the daily transfer of billing records from an exchange to a centralized revenue accounting center

The transactions in the first two groups support the set-up of calls, and are known as “on-line” transactions They have to be executed with minimal delays, since they add to the overall time to set up a call, and usually require two short messages

The transactions in the third and fourth groups are “off-line.” They are less time-critical, and usually require more-and longer-messages

13.2.1 Application Service Elements

We say that a signaling point (SP) performs a set of functions in a telecom- munication network In the CCITT/ITU-T model of signaling system No.7, each function (application) that requires remote operations has an application service element (ASE), which handles the signaling aspects for that application [4-61 In Fig 13.2-1, SP-A is an exchange equipped for two transaction types, and has two ASEs INASE handles the signaling messages for IN services, and OMASE takes care of the messages in operation/administration/maintenance (OM) transactions The INASE and OMASE in SP-A communicate with their respective “peers” in an IN database (SP-B), and in an OAM center (SP-C) The messages exchanged between ASEs are known as components

13.2.2 infrastructure for Transactions

Figure 13.2-2 shows the SS7 entities at a signaling point that are involved in the transfer of transaction messages

382

Signaling Point C

(OAM Center)

Signaling Point A Signaling Point B (Echange) (Network Database)

Components - Components

Figure 13.24 Application service elements

The ASEs in a signaling point are the users of the transaction capabilities application part (TCAP) of signaling system No.7 In turn, TCAP is a user of the signaling connection controlpart (SCCP), and SCCP uses the services of the message transfer part (MTP) (Chapter 8)

In the CCITT/ITU-T model of SS7, an ASE passes its outgoing components

to TCAP, in TC-request primitives TCAP places one or more components in a TCAP message (or TCAP package), which is passed to SCCP in a N-unitdata request SCCP then builds a SCCP message, and passes it to MTP in a MTP- transfer request Finally, MTP forms a message signal unit (MSU), which is sent out on a signaling link (Section 8.8)

Incoming components arrive in MSUs on a signaling link MTP extracts the SCCP message, and passes it to SCCP in a MTP-transfer indication In turn,

Signaling Point A

7 TC-Primitives 7 f - _ -_ Components

TCAP N-UNITDATA

Primitives I - TCAP Message (Package)

SCCP MTP-Transfer

Primitives I

+ -m-s - SCCP Message

MTP

A

Link Figure 13.2-2 Architecture for transactions

SCCP extracts the TCAP package, and passes it to TCAP in a N-unitdata indication Finally, TCAP extracts the component(s) and passes them to the appropriate ASE, in TC-indications

SCCP and TCAP are described in Chapters 14 and 15

13.2.3 Application Independence of TCAP

In Fig 13.2-1, the ASEs are dedicated to specific applications TCAP serves all ASEs at a signaling point, and is specified as an application-independent protocol

13.2.4 Identification of ASEs

Within a signaling point, an ASE is identified by a subsystem number (SSN) In

a telecommunication network, an ASE is uniquely identified by the point code (PC) of its signaling point, and its SSN The combination PC + SSN is known as the “SCCP address” of an ASE, and is used by SCCP to deliver transaction messages to their destination ASEs

13.3 ACRONYMS

ANSI

ASE

CCIS

CCITT

IN

INASE

ISDN

ISUP

ITU

ITU-T

MS

MSU

MTP

OAM

OMASE

PC

SCCP

SP

SSN

SS6

ss7

TCAP

TUP

American National Standards Institute

Application service element

Common-channel interoffice signaling

International Telegraph and Telephone Consultative Committee Intelligent network

ASE for intelligent network applications

Integrated services digital network

ISDN user part

International Telecommunication Union

Telecommunication standards department of ITU

Mobile station

Message signal unit

Message transfer part

Operations, administration and maintenance center

ASE for operational, administrative and maintenance applications Point code

Signaling connection control part

Signaling point

Subsystem number

Signaling system No.6

Signaling system No.7

Transaction capabilities application part

Telephone user part

13.4 REFERENCES

1 A.R Modaressi, R.A Skoog, “Signaling System No.7: A Tutorial,” IEEE Comm Mag., 28, no.7, July 1990

2 R Manterfield, Common Channel Signalling, Peter Peregrinus Ltd, London, 1991

3 T.W Johnson, B Law, P Anius, “CCITT Signalling system No.7: Transaction Capabilities,” Br Telecomm Erg., 7, April 1988

4 Specifications of Signalling System No 7, Rec Q.700, CCITT Blue Book, VI.7, ITU, Geneva, 1989

5 Specifications of Signalling System No 7, Rec Q.771, CCITT Blue Book, VI.9, ITU, Geneva, 1989

6 Ibid., Rec Q.775