Basic SS7 Network Components

 

Network Symbols

Below are the four basic components used in an SS7 network. In network diagrams, these symbols are often used to represent their respective components.

 

Component and Link Placement

The generic network diagram below uses the American National Standards Institute (ANSI) SS7 variant as the point of reference. It illustrates the placement of each network component and all possible link types that may connect points on the network.

 

Six types of links may be used in an ANSI SS7 network. Not all six are always used, and not every type can be connected to certain types of points. For example, by design, some software may only be used with A, E, and F links because it is used as an SSP or SCP.

Note: In other variants of SS7 networks, links are used between signaling points but not differentiated by types - i.e., A links, B links, etc. More detail about SS7 network variants is provided in the Network Architecture section of this module.

 

SSP = Service Switching Point

SSPs are the "brains" of the SS7 network and are usually located at phone switches. Because signaling messages will either originate or terminate within them, SSPs are considered "end points" on a network.

 

The core function of an SSP is to process calls that originate, tandem, or terminate at a specific office. For any given call, the SSP may generate signaling messages to transfer call-related information to other SSPs, or may send a query to an SCP database for instructions on routing the call.

                                

STP = Signal Transfer Point

Similar to switching points in a Public Switched Telephone Network (PSTN), an SS7 network has STPs to relay signaling messages. An STP is a packet switch that acts as a hub to transfer messages to other STPs, SCP databases, or SSPs.

 

Since an STP's core function is to route signals, the need for direct connections between end points on a network is eliminated. The STP routes messages by checking routing information attached to each signaling message and sending it (via the proper link) to the desired signaling point.                                                

 

SCP = Service Control Point

An SCP is a database (or a collection of databases) that holds information required to provide services that are more complex than basic call control (e.g., providing a business with an 800 number). SSPs send queries via signaling messages to SCPs that use the databases housed within them. SCPs then send requested data or instructions back to the querying SSPs.         

 

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