Basic Concept of Signaling SS7

Message Transfer Part (MTP) is mainly responsible for transmitting "User Part" signaling messages across the SS No. 7 network. If a system or signaling network is faulty, MTP can take measures to prevent messages from losing, and repeatedly or disorderly transmitting. MTP consists of signaling data links, signaling link functions, and signaling network functions.

Here are the following exchange in SS7

Signaling point (SP):
A signaling point is a node of SS7. It can be identified by signaling point code (SPC). Source signaling point refers to a signaling point that generates signaling messages. Destination signaling point refers to a signaling point that receives signaling messages. In general, international SPC is 14-bit and national SPC is 24-bit.

Signaling link: 
A signaling link is a physical link that connects signaling points and transmits signaling messages.

Signaling network:
Logically, a signaling network is separated from a communication network. It is used to transmit signaling messages. A signaling network mainly consists of signaling points and signaling links.

Signaling link set:
A signaling link set is a set of parallel signaling links that directly connects two signaling points.

Signaling route:
A signaling route is a route that transmits signaling messages from source signaling point to destination signaling point.

Signaling transfer point (STP):
A signaling transfer point is neither a source signaling point, nor a destination signaling point. It is a signaling point that transfers signaling messages. If a signaling transfer point can serve as a signaling point, it is called an integrated STP. If a signaling transfer point cannot serve as a signaling point, it is called an individual STP.

There are the following two working modes:

Associated: 
Three signaling points (VMSC, GMSC, and VMSC) cannot serve as an STP. The signaling messages between VMSC and GMSC are transmitted through a directly connected signaling link. GMSC can serve as a voice transfer path; however, GMSC cannot serve as a signaling transfer point.If SS7 signaling messages are transmitted through two or more signaling links with one or more STPs, it is called quasi-direct connection. Figure 1-2 shows the quasi-direct connection.

Quasi-associated: 

There is a direct voice path between VMSC and VMSC; however, there is no direct signaling link between VMSC and VMSC. Signaling messages between VMSC and VMSC are transferred by GMSC. GMSC serves as an integrated STP.