Compare the architecture of SS7 with seven-layer OSI architecture

The relationship among these levels and the layers of the OSI model is demonstrated in figure. The user part includes layers 4 to 7 of the OSI model.

FIG - Relationship between CCITT No.7 Functional levels and OSI layers

Level 1 is implies that of sending bit streams over a physical path. This uses times slot 24 of a 1.5 M bit/s system or times lot 16 of a 2 M bit/s PCM system.

Level 2 performs the functions of link initialization, error control, error rate monitoring, delineation of messages and flow control.

Level 3 gives the functions needed for a signaling network. All nodes in the network have a single point odd that is a 14 bit address. All messages contain point codes of the originating and terminating nodes for such messages.

Levels 1 to 3 by the message transfer part (MTP) of CCITT number 7.

Level 4 is the user part. It consists of the processes for handling the service being supported through the signaling system. The message transfer part is able of supporting various different user parts. Therefore as far, three have been explained: the telephone user part (TUE), the (ISDN) user part (ISDN-UP) and the data user part (DUP).