Basic SS7 Network Components (Cont.)

A = Access

This type of link provides signaling end points (i.e., SSPs and SCPs) with access to an SS7 network. An A link is used to connect an SSP or SCP to STPs throughout the network.

B = Bridge

This type of link interconnects STPs throughout a network. Two B links are usually located between STPs. Those B links act as a "bridge" to transfer signaling messages to network points not directly accessible by the originating STP.

Little difference exists between the function and the purpose of B and D links. Therefore, these links are sometimes referred to as B/D links. (Further explanation of D links is provided in this section.)

C = Cross

A C link connects a "mated pair" of STPs. An STP and its mate can perform the same operations. Therefore, if an STP cannot, because of link failures, send a signaling message to another point on the network, the STP can send the message to its mate, which can then send the message to that point.

D = Diagonal

The D link connects an end point's (i.e., SSP or SCP) primary STP pair to a secondary STP pair in a diagonal manner. A pair of D links is used to transmit signaling messages between STPs.

Little difference exists between the function and the purpose of B and D links. Therefore, these links are sometimes referred to as B/D links.

E = Extended

An E link is used to provide an SSP with a link to an alternate STP. An E link is used if neither of an SSP's A links were in service to access the primary STPs. E links are only used in cases where the highest level of signaling reliability is desired. In most cases, however, this is not required because of the redundancy already provided by an SS7 network.

F = Fully associated

An F link is used to provide a direct connection between signaling endpoints. An F link can potentially be used to connect:

• SSP to SSP
• SCP to SCP
• SSP to SCP

However, F links are not normally used in networks that employ STPs.

Network Boards

An SSP consists of one or more computing elements that use a network board to interface with an SS7 network. The two common types of boards are: v.35 and T1/E1. However, the v.35 board is being used less because of the technological advantages provided by a T1/E1 board.

Both v.35 and T1/E1 cards are designed within International Telecommunications Union (ITU) standards for high-speed synchronous, bidirectional data exchange. The T1 version of the T1/E1 card and the v.35 card are used in North American networks. The E1 version of the T1/E1 card is used throughout Europe.

The T1/E1 card requires a cable with a connector similar in appearance to a common telephone connector. The v.35 card requires a cable with a connector similar to a computer printer cable.

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