)-The STP is responsible for translating the SS7 messages and then routing those messages between the appropriate network nodes and databases. Notice in Figure 4.13 that the SCPs and the STPs are both redundant and that the links running between them are also redundant. If a network loses its signaling system, it loses the capability to complete calls, as well as to do any form of billing or passing along of management information. This makes SS7 critical. The SS7 signaling data link, as mentioned earlier in the chapter, is a full-duplex digital transmission channel that operates at either 56Kbps or 64Kbps. A variety of other SS7 links are defined as well, and each has specific uses within the signaling network: A (access) links-An A link interconnects an STP with either an SSP or an SCP. The SSP and SCP, collectively, are referred to as the signaling endpoints. A message sent to and from the SSPs or SCPs first goes to its home STP, which, in turn, processes or routes the message. Intelligent Networks B (bridge) links, D (diagonal) links, and B/D links-A B link connects an STP to another STP. Typically, a quad of B links interconnect peer (or pri- mary) STPs (e.g., the STPs from one network to the STPs of another net- work). The distinction between a B link and a D link is rather arbitrary, and such links may be referred to as B/D links. C (cross) links-C links interconnect mated STPs. E (extended) links-E links provide enhanced reliability by providing a set of links from the SSP to a second STP pair. F (fully associated) links-F links are links that directly connect to signal- ing endpoints. Intelligent Networks The ITU's standardization of SS7 in 1980 began the evolution toward the concept of intelligent networking. An IN includes a set of nodes that rely on widespread distribution of call-handling functions and capabilities (see Figure 4.14). Before the advent of INs, customers could have only the services and features available from their local exchanges. Their ability to demand and achieve new services from