Design of a Fast Restoration Mechanism for Virtual Path-based Atm Networks. 5 Numerical Results

9] H. Fujii and N.Yoshikai. Restoration message transfer mechanism and restoration characteristics of double-search self-healing ATM network. 14] Draft new ITU-T recommendation Q.SAAL.0:. B-ISDN signaling ATM adaptation layer. Figure 9: Bypasses existence in the case of diierent probabilities of used VPs 6 Conclusion We have proposed a protocol for exible rerouting of VCs when the underlying VPs fail in ATM networks. The protocol is a trade-oo between the backup VP protocol, that requires stringent management of backup VP's and the complete VP reconstruction protocol, that has a large latency. The protocol uses simple operations at the endpoints of the rerouted VP and of the backup VP's to perform the construction of the new VP and the rerouting of the VC's. Calculations show that the extra rerouting time of FRP compared to the backup VP is small, while providing greater management exibility. In this section we compare the rerouting times for three schemes: FRP, the backup VP scheme and complete VP reconstruction. In addition we give an estimate of the probability of nding an alternate route of concatenated stand-by VP's in a network. For the comparison, we assume a bypass for a given VP that is built of 5 stand-by VP's, each consisting of 4 links on the average and whose total geographic length is 1000 km. The rerouting time, in msec, for each method is estimated as in Table 1: backup VP FRP VP reconstruction bypass search 0.2 0.2 propagation time 8 8 8 VCT operations 1.6 1.6 1.6 concat operations 1.6 7.6 switch time for intermediate 2 9.5 switch time for endpoints 1 1 1 total 10.6 14.4 27.9 Table 1: The rerouting time, in msec, for the diierent methods The bypass search time is the time it takes the rerouting endpoint to nd a path. We estimated this time by writing a simulation C++ program on a SUN Ultra4 for nding a bypass in the UUNET High-Speed backbone 1 with random VP layout. We have measured this time as 0.2 msec. The propagation time of the REROUTE and REROUTE-ACK messages depends on the geographic length of the bypass and in our example is 4 msec in each direction 8]. We also implemented the VCT and VPT operations and measured the processing time of the VCT-move and VCT-update in one endpoint switch as 0.8 ms and the VPT-concat operation in each intermediate switch as 0.4 ms. Therefore, the concatenation …