An Introduction to SS7

yhyang

ABSTRACT ..........................................................................................................................4
1 INTRODUCTION..........................................................................................................4
2 BACKGROUND AND HISTORICAL PERSPECTIVE ......................................................4
Figure 2.1: In Band Signaling: CAS..................................................................5
Figure 2.2: Out of Band Signaling: CCS ..........................................................5
3 PRINCIPLES OF SS7 SIGNALING: THE SIGNALING LINK............................................5
Figure 3.1: Overview of SS7 Stack ..................................................................6
Figure 3.2: Links and Linksets ........................................................................6
Figure 3.3: Routes and Routesets ....................................................................7
4 PRINCIPLES OF SS7 SIGNALING: THE PROTOCOL STACK ........................................7
4.1 THE MESSAGE TRANSFER PART ........................................................................7
Figure 4.1: Layer 2 Message Structure ............................................................8
4.2 LAYER 4 CALL CONTROL PROTOCOLS, TUP AND ISUP ................................9
Figure 4.2.1: Example TUP Call Sequence ....................................................10
Figure 4.2.2: Example ISUP Call Sequence ..................................................11
4.3 DATA USER PART, DUP ..................................................................................11
4.4 SIGNALING CONNECTION CONTROL PART, SCCP ......................................11
Figure 4.3.1: SCCP Global Title Translation: ................................................12
4.5 TRANSACTION CAPABILITIES APPLICATION PART, TCAP ............................12
4.6 MAP, INAP, IS41 ..............................................................................................13
5 MESSAGE TRANSMISSION, SECURITY AND ERROR CORRECTION ........................13
Figure 5.1: Message Acknowledgement ........................................................13
6 NETWORK ARCHITECTURE AND ELEMENTS............................................................15
6.1 NETWORK STRUCTURE ..................................................................................15
Figure 6.1.1: The SSP ....................................................................................15
Figure 6.1.2: Tandem Exchanges ..................................................................15
Figure 6.1.3: Signaling Overlay Network ......................................................16
6.2 NETWORK ELEMENTS......................................................................................16
6.2.1 The Local Exchange, Class 5 or Service Switching Point....................................16
6.2.2 The Tandem or Class 4 Switch ..........................................................................17
6.2.3 The Signal Transfer Point or STP........................................................................17
Figure 6.2.3.1: Combined Linksets ................................................................17
Figure 6.2.3.2 Primary and Secondary Routing..............................................17
6.2.4 The Service Control Point or SCP ......................................................................17
6.2.5 The Service Data Point or SDP ..........................................................................18
6.2.6 The Intelligent Peripheral or IP ..........................................................................18
6.3 SIGNALING MODES ........................................................................................18
6.3.1 Signaling Connectivity ......................................................................................18
Figure 6.3.1.1: Fully Associated Signaling ....................................................18
Figure 6.3.1.2: Non Associated Signaling ......................................................18
Figure 6.3.1.3: Quasi Associated Signaling....................................................18
6.3.2 Signaling Link Definitions..................................................................................19
Figure 6.3.2.1: Access Links ..........................................................................19
Figure 6.3.2.2: Bridge Links ..........................................................................19
Figure 6.3.2.3: Cross Links ............................................................................19
Figure 6.3.2.4: Diagonal Links ......................................................................19
Figure 6.3.2.5: Extended Links ......................................................................20
Figure 6.3.2.6: Fully Associated Links ..........................................................20
7 NATIONAL IMPLEMENTATIONS AND ARCHITECTURAL VARIATIONS ..................20
8 SS7 AND ENHANCED SERVICES................................................................................21
Figure 8.1: Overview of an IN Enabled Network ..........................................21
9 SS7 IN MOBILE NETWORKS ......................................................................................22
Figure 9.1: Overview of a GSM Mobile Network..........................................23
10 SS7 IN MOBILE NETWORKS ......................................................................................23
Figure 10.1: SIGTRAN Architecture ..............................................................24
11 THE FUTURE OF SS7..................................................................................................24
12 BROOKTROUT AND SS7 ..........................................................................................25

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