Chapter 4: Signalling and Routing4-109A656-04 and 9A600 Configuration Guide4.3.4 GCACGCAC (generic Call Admission Control) is used by switches supporting PNNI to increase thechances that a requested connection can be supported by all switches in the determined path.Since each ATM switch in the path may perform CAC in a different way, it is necessary for ageneric CAC to examine the current state of the network topology (via current topology stateinformation provided by the PNNI protocol) to determine if the switches will be able tosupport a requested connection. This is part of the PNNI 1.0 specification, and all ATMswitches supporting PNNI 1.0 will perform GCAC. Through this process, the first switch willattempt to route the call to switches that it estimates will be able to meet the QoSrequirements, reducing the chances of crankback occurring extensively throughout thenetwork, thereby making the network more efficient.4.3.5 AddressingPNNI switches advertise their reachable addresses to the other members of their peer groups.Whenever possible, these addresses are summarized. This is done via advertising one or morecommon address prefixes that the range of addresses share. This restricts the amount of dataPNNI switches produce when advertising their addressing information and reduces the size ofthe address database. If there are any addresses that can not be summarized, the full addressesare advertised to the peer group members.4.4 IISP OVERVIEWIISP, also referred to as PNNI Phase 0, ensures ATM switch vendor inter-operability across theATM network using legacy (pre-PNNI 1.0) ATM switches. IISP requires static routes to beconfigured between switches. The SmartSwitch 9500 supports IISP 3.0, 3.1 and 4.0 protocolstacks on each interface. Each interface may be configured by the user via the MIB commandscovered in the following sections, but may also be autoconfigured.4.4.1 Supported UNI Signalling VersionsThe 9A656-04 supports the following UNI Signalling specifications for IISP connections:• UNI 3.0• UNI 3.1• UNI 4.04.4.2 UNI SidesThe 9A656-04 supports both network and user side UNI Signalling for IISP connections.
