Chapter 6. Configuration60 ISU 2x64 Dual Port ISDN Service Unit User Manual 61200051L1-1DThe primary usage for SAP is general purpose asynchronous rateadaptation in a dial-up or leased environment. SAP only oper-ates on a 64 kbps data link. Figure 6-21 illustrates the menu pathfor selecting SAP.FALLBACKThe FALLBACK asynchronous rate adaptation protocol providesthe capability to automatically establish calls with other ISDNterminal adapters and Switched 56 DSUs, as well as other ISUsusing a single configuration. The ISU 2x64 must be optioned asfollows for FALLBACK operation:1. Any asynchronous bit rate up to 115.2 kbps which is support-ed by the DTE.2. Flow control must be enabled and supported by the DTE.FALLBACK supports the following protocols based on the CallType: BONDING mode 1, V.120, and T-Link. Figure 6-21 illus-trates the menu path for selecting FALLBACK.When answering calls, the ISU 2x64 uses the incoming call typeto determine which rate adaptation protocols to support.Table 6-ARate Adaptation ProtocolsCall Type Rate Adaption ProtocolsSupported Typical Units SupportedData 64 k Bonding mode 1 ISUsV.120 ISDN TAsPPP async-sync PPP compatible bridges/routersData 56 k BONDING mode 1 ISUsV.120 ISDN TAsPPP async-sync PPP compatible bridges/routersT-Link 2-wire Switched 56 DSUs
