The SS7 (Signaling System No. 7) protocol architecture consists of four main functional layers:
- Message Transfer Part (MTP):
The MTP is responsible for the reliable and efficient transport of signaling messages between network elements. It provides a variety of functions such as message routing, error checking, message sequencing, and congestion control. The MTP is divided into three sublayers: MTP Level 1, MTP Level 2, and MTP Level 3.
- MTP Level 1: Provides the physical interface between network elements and specifies the electrical, mechanical, and functional characteristics of the signaling links.
- MTP Level 2: Provides the link-level functions such as error detection and correction, message alignment, and flow control.
- MTP Level 3: Provides the network-level functions such as message routing, congestion control, and network management.
- Signaling Connection Control Part (SCCP):
The SCCP provides additional routing and addressing information for signaling messages. It enables efficient message routing by allowing the use of unique network addresses and providing network routing capabilities based on various parameters. The SCCP also provides services for message segmentation and reassembly, as well as connection-oriented and connectionless communication.
- Telephone User Part (TUP):
The TUP is responsible for handling telephone call control functions such as call setup, teardown, and call forwarding. It provides signaling messages for setting up and managing voice calls in traditional telephone networks.
- Integrated Services Digital Network User Part (ISUP):
The ISUP is responsible for handling call control functions in digital networks such as ISDN and cellular networks. It provides signaling messages for setting up and managing voice calls and other services such as call forwarding, call waiting, and caller ID.
The SS7 protocol architecture also includes a variety of management and maintenance functions such as network monitoring, fault detection, and error reporting. These functions are typically performed by network management systems that use the SS7 protocol to exchange management information with network elements. Overall, the SS7 protocol architecture is designed to provide reliable and efficient signaling and communication between network elements, enabling the provision of a wide range of voice and data services in modern telecommunications networks.