/s VC-3-Xv 1 to 256 48,384 Kbit/s 48,384 to 12,386 Kbit/s Higher Order VC-4-Xv 1 to 256 149,760 Kbit/s 149,760 to 38,338,560 Kbit/s Fig. 11.6 Low- and high-order VCAT payload containers and their capacities. Contiguous Virtual Service Bitrate Concatenation Concatenation Ethernet 10 Mbit/s VC-3 (20%) VC-12-5v (92%) Fast Ethernet 100 Mbit/s VC-4 (67%) VC-3-2v (100%) Gigabit Ethernet 1000 Mbit/s VC-4-16c (42%) VC-4-7v (95%) FICON 850 Mbit/s VC-4-16c (35%) VC-4-6v (94%) ESCON 200 Mbit/s VC-4-4c (33%) VC-3-4v (100%) Comparison of transport efficiencies for contiguous and virtually concatenated solutions. Concatenation VCAT Interfaces STM-16 t=0: A to D: 8 X VC-4 B to E: 8 X VC-4 t=T1: A to D: Release 2 X VC-4 B to E: Release 3 X VC-4 t= T2: C to F: Request a VC-4-4c Virtual Concatenation Allows Free SUCCESS! Bandwidth to Be Used More Efficiently Fig. 11.8 Virtual concatenation as a means to overcome the problem of fragmentation. be given a fraction of this total bandwidth as transmission capacity in accordance with its usage requirements. VCAT also eliminates the fragmentation problem associated with contiguous concatena- tion. Returning to the previous example where a request for a 622-Mbit/s (VC-4-4c) connec- tion from C to F failed using contiguous concatenation, virtual concatenation only requires the interfaces to be upgraded and allows the VC-4s to be routed independently across the SDH network (see Figure 11.8). The existing SDH network elements continue to switch at the VC-4 granularity (in this example) and are transparent to the virtual concatenation process. Now the request to interconnect C and F with a VC-4-4c is successful because VCAT allows the use of the available noncontiguous VC-4s. High-Order VCAT Figure 11.9 illustrates the process for a high-order C-n-Xc container that is split across X individual C-n containers of a VC-n-Xv structure. The frame structure of a high-order virtual HO VCAT Payload Containers VC-n-Xv C-n-Xc pVC-4-Xv VC-3-Xv 125 us P + 1 P + 1 VC-n (X) VC-n-Xv VC-n (1) Fig. 11.9 Princ