The ISUP protocol is a circuit-related protocol that is used primarily for establishing connections between exchanges for the transmission of bearer traffic. The bearer traffic, which usually is generated by subscribers, can consist of voice, data, video, multimedia, or audio. In today s network, only voice and data are achievable. Through the development of technologies such as ATM and BISDN, video and multimedia also will be available through the PSTN.

Regardless of the technology ISUP provides the mechanism for establishing the connections from the originating exchange to the destination exchange without using the bearer circuit itself. In addition to connection establishment, ISUP also provides a means for passing information between exchanges associated with a call that is already in progress. However, the connection already must be established and the information must be related to that call s circuit or services. Any information about the subscriber or network features or anything that is not directly related to the circuit itself uses the TCAP. This protocol was established (as described in Chapter 10) for non-circuit-related messages.

The type of information provided by the ISUP protocol includes resource requirements for completion of the connection (resources such as ISUP all the way through the network and echo cancelers on the voice circuit). Bandwidth information and service information (call waiting and call forwarding, for example) are service-related and require that information be sent between both end-to-end exchanges.

Intermediate exchanges do not need to see this information because it does not involve their...