SCCP Signaling Analysis and Process

Chapter 1 General

1.1 Limitation of MTP Transmission

.The signaling point code is not the standard international code, it is only effective within a certain network.

.The limited capacity of the signaling point code (14-bit as specified by CCITT) also limits the number of the signaling point to be marked.

.The 4-bit SI can not satisfy the increased requirements of the modern communication as well, since it can only be assigned to sixteen different user parts.

.Finally, MTP can only provide the connectionless transmission

1.2 The Location of SCCP in CCS7

.When SCCP and MTP is combined together, they are called as NSP (network service part).

.SCCP and MTP-3 all locate in the network layer of the OSI model.

Chapter 2 Features and Functions of SCCP

2.1 Application Features of SCCP

.Enable to transfer both circuit related and non-circuit-related signalling and user information in telecommunication networks.

.Provide enhanced addressing and routing function, and enable to achieve the direct global transmission between different CCS7 networks.

.Enable to provide connectionless service and connection-oriented network service.

There are two kinds of service provided by the SCCP protocol:

1.Connectionless Service
2.Connection-Oriented Service

2.2 Service Functions of SCCP Network

The four classes are:

0 Basic connectionless class

1 In-sequence delivery connectionless class

2 Basic connection-oriented class

3 Flow control connection-oriented class

2.2.1 Connectionless services

.In the connectionless service, the routing information must be contained in each data packet.

.No logical connection is established between the end nodes.

.The connectionless SCCP offers two services:

-The class 0 service allows the SCCP to insert SLS values randomly, or with the aim to achieve an appropriate load sharing within the underlying MTP network;

-The class 1 service requires the SCCP to insert the same SLS for all the SCCP-SDUs (service data unit) associated with given parameters "sequence control" and "called address".

Message type : UDT UDTS XUDT XUDTS

Message type code: 0x09 0x0A 0x11 0x12

Among this：

UDT----unit data

UDTS----unit data service

XUDT----extend unit data

XUDTS---extend unit data service

SCCP procedure of connectionless class

2.2.2 Connection-oriented service

.Connection-oriented network service is a way to realize the exchange of signalling information by establishing a logical signaling connection between the network service users.

.The logical signaling connection is achieved by giving a local reference number to the signaling messages belonging together.

Chapter 3 Addressing and Routing Functions of SCCP

Addressing with in the SCCP of CCS7 makes use of three separate elements:

DPC;

Global Title (GT);

Sub-System Number (SSN);

There are two basic categories of SCCP routing

DPC+SSN

An Example:

Chapter 4 Brief Introduction to SCCP Message Format

Message Example

Brief Introduction to Important Parameters of SCCP Message

1. Protocol class

The "protocol class" parameter field is a one-octet parameter and is structured as follows:

Message Example

data pointer

2. Address
Address

Address indicator

SSN

Address indicator

GT Code

Type 4 GT

Address Indicator

message example

This is a SCCP message began with SIO.
83 11 FF 03 09 FF 05 0D 09 81 03 0E 18 0B 12 06 00 12 04 68 31 39 31 00 00 0A 12 07 00 12 04 68 31 09 40 67 2A 62 28 48 04 2B 81 11 00 6C 80 A1 80 02 01 00 02 01 02 30 16 04 08 64 00 30 31 08 00 51 F4 81 06 91 68 31 09 40 67 00 00 00 00