ished and the connection request has to be denied. Over time and for large networks, the unused bandwidth containers accumulate and result in suboptimal use of network bandwidth and a higher number of connection failures for contiguously concatenated payload services. One solution would be to regroom the network to recover this "stranded" bandwidth. However, in some situations regrooming might not be an option because this is akin to "defragging" the network and is potentially risky for a network operator. The alternative is to simply increase the network capacity and tolerate the inefficiencies. Another disadvantage of contiguous concatenation is the mismatch in bandwidth gran- ularity between connectionless and packet-oriented technologies, such as IP or Ethernet, and the rigid bandwidth granularity provided by contiguous concatenation. For example, Concatenation Service Bitrate Contiguous Concatenation Ethernet 10 Mbit/s VC-3 (20%) Fast Ethernet 100 Mbit/s VC-4 (67%) Gigabit Ethernet 1000 Mbit/s VC-4-16c (42%) FICON 1000 Mbit/s VC-4-16c (35%) Fig. 11.4 Contiguous-concatenation service mappings and efficiencies. ESCON 200 Mbit/s VC-4-4c (33%) SDH Network Interfaces Interfaces MEI =j+1 MFI = k + 1 Source (t1 + 125 us) (to + 125 us) VC-4-7 VC-4-7 VCG Members MFI = j MFI = k MFI = j MFI = k SQ = 0-6 SQ = 0-6 Contiguous Contiguous Payloads Payloads Fig. 11.5 Generic diagram of the principle of operation. to transport a single Gigabit Ethernet service, it would be necessary to allocate a VC-4-16c container, which has a capacity of 2.4 Gbit/s-more than double the necessary bandwidth. Further examples are given in Figure 11.4. Virtual Concatenation Virtual concatenation is a solution, standardized by ITU-T G.707, that allows granular increments of bandwidth in single VC-n units and solves the problems previously high- lighted for contiguous concatenation. VCAT also creates a continuous payload equivalent to X times the VC-n units at the source, but each container is individually transported across the SDH network towa