ISUP Signaling Analysis and Process

Corresponding Relations of SS7 with OSI Seven-layer Architecture

OSI layer

ISUP Message Format
ISUB Message

F: Signal Unit Pegging Flag                 CK: Error Detecting Code
LI: Length Indicator                            DPC: Destination Signaling Point
SIO: Service Indicator                        OPC: Origination Signaling Point
SIF: Signaling Message                       CIC: Circuit Identification Code
FSN: Forward Sequence Number       BSN: Backward Sequence Number
FIB: Forward Retransmission Ind.       BIB: Backward Retransmission Ind.

SIO

SIO

ISUP Message Architecture
ISUP

IAM Architecture and Parameters

Message Trace

IAM Message Architecture

Message Trace1

IAM Message Architecture example
<ISUP NAT 1091 IAM 0000158 00E 15093B 150202   01 60 00 F8 00 02
07 05 01 10 03 80 03 08 01 00 0A 07 03 13 98 68 81 86 69 00

01 60 00 F8 00 Mandatory Fixed Part;
02 07      Mandatory Variable part and Optional part pointers
05 01 10 03 80 03     Mandatory Variable part (called Number)
01 00 description part of optional parameter encoding
The parameter identification number of calling number is 0A, and the calling number is 0A
07 03 13 98 68 81 86 69. So we can ensure the caller number is 898 6186896
07 after 0A means the called length is 7 bits. 03 13 is the description part of caller. 0A 07
03 13 98 68 81 86 69

IAM Mandatory Fixed Part
IAM message

IAM Mandatory Variable Part

IAM message Trace

REL Message Architecture and Parameter

Release Message

REL message Architecture

ISUP

<ISUP NAT 5769 REL 0000198 006
15093B 150202 02 00 02 80 90
02 00 are the pointers of mandatory variable parameter and optional parameter respectively. There is no optional parameter, so it is 00.
02 80 90 are the cause indicator. In it the cause value is 90, i.e. normal call clearing.

ISUP normal message process

ISUP failure process

ISUP trunk management

Switch system

Introduction to ISUP Module Function of Switching System
    .Brief Introduction
    .Call Handling Flow
    .Processing Flow with MTP
    .Management to circuit for ISUP
    .Subscriber Interface

Software Architecture