7 signaling: SCCP layer Overview

 

1. Reasons for SCCP introduction:

Communication networks and new communication services are constantly evolving. Messages irrelevant to the call circuit must be transmitted.

The uncertain relationship between call-related messages and Circuits

Limitations of DPC addressing

Restrictions of Si

Ø there are a large number of non-real-time messages on the network, and virtual connections need to be established in advance

 

2. SCCP features:

Various non-Circuit-related signaling messages can be transmitted.

Ø with enhanced addressing routing, direct transmission of signaling can be achieved between different 7th Signaling Networks in the global interconnection.

In addition to the no-connection service function, it can also provide connection-oriented service functions

 

3. SCCP network service functions:

The SCCP layer provides connectionless and connection-oriented services to users. Based on their different needs for services, it provides the following four types of services to deliver services with different quality requirements:

Ø basically no connection services

Ø sequential non-sequential services

Basic connection services

Ø connection-oriented traffic control

 

4. connectionless services:

A) category:

Class 0 business: each message is transmitted independently and has no relationship with each other. Therefore, it cannot be ensured that the message is sent to the destination signaling point in the order of sending;

Businesses 1: attach the same Signaling Link selection field SLS to the data information from the same information flow to ensure that the data information is transmitted through the same Signaling Link. Therefore, the destination signaling point can be reached in the sending order.

B) Message Type:

The connectionless service provides four types of messages, which are encoded as follows:

Message Type UDT udts xudt xudts

Message Type Code 0x09 0x0a 0x11 0x12

Where: UDT --- unit data

Udts --- unit data sevice

Xudt ---- extend unit data

Xudts ---- extend unit data service

C) message process:

No connection SCCP program. Transmits unrelated UDT Based on the destination signaling point encoding in each message. If the UDT cannot be transmitted by the relay signaling point due to a fault, the udts message will be sent back to the initiator.

 

5. Addressing routing of SCCP:

The SCCP layer encoding function includes two aspects:

Ø address decoding

Ø select a reachable destination. The destination can be a subsystem of a certain signaling point or only a signaling point.

 

SCCP layer addressing routing method:

Ø DPC + SSN

Ø GT

 

6. GT:

Concept:

The global title (GT) is a global name that makes sense globally. It can directly transmit circuit-independent messages between any two signaling points in the world. Generally, it is a user dialing, flexible routing using GT is an important feature of SCCP.

Composition:

• Encoding scheme:

1 indicates the parity of the number of address signals in the address information, 1 indicates the odd number of address signals, and 2 indicates the even number of address signals.

• Number plan:

Use a digit to indicate the ID of the address information. The common GSM code is as follows:

01: ISDN/telephone no. Plan (e.163/e.164 );

05: maritime user ID Plan (e.210/e.211 );

06: Land Mobile Number Plan (e.212 );

07: ISDN/land mobile number Plan (e.214 ).

• Address representation:

Specify the attribute of the address information, which is encoded as follows (in binary format ):

Idle -- 000000

User number -- 000001

Domestic backup-000010

Valid domestic number-000011

International number -- 000100

For example, in GT code 40001140861390666, the GT stands for 40, the translation type is 00, the numbering plan is ISDN/telephone numbering plan, and the address is an international number.

 

7. SCCP management functions:

Trace the available status and unavailable status of the signaling point, the current node subsystem, and the remote node subsystem, and the congestion status of the signaling point.

Forward the signaling service to the backup subsystem of the same signaling point or different signaling points based on the above information.

Ø Master/Slave subsystem Switching

 

8. SCCP business interface:

Same layer: request and response

Inter-layer: Indication and confirmation

 

9. SCCP message structure:

SCCP messages are encapsulated in mtp msu (message signal unit) and sent out. For MSU, SCCP messages are its SIF fields.

It consists of the following parts:

• Routing selection label structure:

OPC + DPC + SLS

• Message Type:

Used to identify different SCCP messages. It is a required byte for all messages and determines the function and format of the message. See the table below:

• UDT Message format:

10. Related Concepts:

Ø subsystem SSN:

Indicates the upper-layer Message Type of SCCP. Different user sections (Common SSN lists are as follows ):

Ø DPC + SSN addressing:

All signaling points in the network (including the source signaling point, destination signaling point, and STP) must be able to identify the destination signaling point encoding DPC. After the signaling message arrives at the intermediate node, it is directly forwarded by the MTP layer, does not pass through the SCCP layer. In this case, many DPC data needs to be configured for the source message and STP.

Ø GT addressing:

It can be used when the destination signaling point encoding DPC is not identified by the source signaling point and part of the STP. When this addressing method is used, the signaling message is sent to STP. After SCCP translates the GT address as the destination signaling point or stp dpc, and then MTP transmits the message. In this case, the source signaling point only needs to send the signaling to STP Based on the GT number crown, and the STP determines the next Sending address. The source signaling point and STP need to configure less DPC data.

 

11. SCCP message example: