MTP Message transfer part

Introduction

The Message Transfer Part (MTP) is a component of the Signaling System 7 (SS7) that is responsible for the reliable transfer of signaling messages between network elements in a telecommunications network. The SS7 network is used for various purposes such as call setup, call routing, and billing. In this article, we will discuss the MTP and its functions in detail.

MTP Architecture

The MTP is divided into three levels, each of which performs a specific function in the signaling process. The first level, MTP Level 1 (MTP1), is responsible for the physical transmission of signaling messages. It defines the physical interface between network elements and provides reliable transmission of messages using error detection and correction techniques.

The second level, MTP Level 2 (MTP2), is responsible for the reliable transfer of messages between network elements. It provides flow control, error correction, and message sequencing to ensure the integrity and reliability of signaling messages. MTP2 also handles congestion control by monitoring the traffic load and delaying message transmission if necessary.

The third level, MTP Level 3 (MTP3), is responsible for message routing and network management. It provides the functions necessary for call setup, routing, and maintenance. MTP3 also manages the signaling linksets and signal transfer points (STPs) in the network.

MTP Functions

The MTP performs several functions that are critical to the operation of a telecommunications network. These functions include message routing, flow control, error detection and correction, message sequencing, and congestion control.

Message Routing

MTP3 is responsible for message routing in the SS7 network. It uses signaling point codes (SPCs) and signaling link codes (SLCs) to route messages between network elements. SPCs identify signaling points, such as switches or service control points (SCPs), while SLCs identify the signaling links that connect these points.

When a message is sent from one network element to another, it is first routed to the appropriate signaling point using the SPC. The message is then routed to the appropriate signaling link using the SLC. Finally, the message is transmitted over the signaling link to the destination network element.

Flow Control

MTP2 provides flow control in the SS7 network. It ensures that messages are transmitted at a rate that the receiving network element can handle. This prevents the receiving network element from being overwhelmed with too many messages at once.

MTP2 uses a credit-based system to control the flow of messages. Each network element is assigned a certain number of credits, which represent the number of messages it can receive at any given time. When a message is sent, the sending network element uses one credit. When the receiving network element acknowledges the message, it returns the credit to the sending network element, allowing it to send another message.

Error Detection and Correction

MTP1 provides error detection and correction in the SS7 network. It uses various techniques such as cyclic redundancy checks (CRCs) and parity bits to detect errors in signaling messages. If an error is detected, MTP1 requests the retransmission of the message.

Message Sequencing

MTP2 provides message sequencing in the SS7 network. It ensures that messages are delivered in the correct order. Each message is assigned a sequence number when it is sent. The receiving network element checks the sequence number of each message it receives to ensure that it is the next message in the sequence.

Congestion Control

MTP2 provides congestion control in the SS7 network. It monitors the traffic load on signaling links and delays message transmission if necessary to prevent network congestion. This ensures that messages are delivered reliably and prevents network failures due to overload.

Conclusion

The Message Transfer Part (MTP) is a critical component of the Signaling System 7 ( SS7) that provides reliable transfer of signaling messages between network elements in a telecommunications network. The MTP is divided into three levels, each of which performs a specific function in the signaling process. MTP1 is responsible for the physical transmission of signaling messages, MTP2 is responsible for the reliable transfer of messages between network elements, and MTP3 is responsible for message routing and network management.

The MTP performs several critical functions in the SS7 network, including message routing, flow control, error detection and correction, message sequencing, and congestion control. These functions ensure the integrity and reliability of signaling messages and prevent network failures due to overload.