Network Services Part (NSP) of SS7
The NSP provides ISDN nodes with a highly reliable and efficient means of exchanging signaling traffic using connectionless services.The NSP allows network nodes to communicate throughout the world without concern for the application or context of the signaling traffic.
Message Transfer Part (MTP) of SS7:
- The function of the MTP is to ensure that signaling traffic can be transferred and delivered reliably between the end-users and the network
- MTP is provided at three levels as shown in figure 8.7
Signaling data link functions (MTP Level 1) provide an interface to the actual physical channel over which communication takes place
- CCITT recommends that MTP Level 1 use 64 kbps transmissions, whereas ANSI recommends 56 kbps
- The minimum data rate provided for telephony control operations is 4.8 kbps
Figure 8.7Functional diagram of message transfer part
Signaling link functions (MTP Level 2) correspond to the second layer inthe OSI reference model and provide a reliable link for the transfer of traffic between two directly connected signaling points
- Variable length packet messages, called message signal units (MSUs), are defined in MTP Level 2
- A wide range of error detection and correction features are provided in MTP Level 2.
- MTP Level 2 also provides flow control data between two signaling points as a means of sensing link failure
- MTP Level 2 uses a timer to detect link failure
Signaling network functions (MTP Level 3)provide procedures that transfer messages between signaling nodes.
- In ISDN, there are two types of MTP Level 3 functions: signaling message handling and signaling network management
- Signaling network management allows the network to reconfigure in case of node failures, and has provisions to allocate alternate routing facilities in the case of congestion or blockage in parts of the network.
- Signaling message handling is used to provide routing, distribution, andtraffic discrimination