In
Figure 10.1, the multiplexing occurs in stages as the STS-1s are first combined into STS-3s,
and then the STS-3s are combined into an STS-48. The STS-48 can be converted directly
into an OC-48 and transmitted through a fiber or passed to another SONET device.
Contiguous Concatenation In SONET, for the transport of payloads that exceed the
payload capacity of the standard set of Synchronous Payload Envelops (SPEs), contiguous
concatenation can be used. As the name implies, the VTs or STSs used for the
concatenation must be adjacent and free of other traffic.
When using SONET contiguous concatenation, contiguous bandwidth must be maintained
throughout the whole transport network. Because of the need to keep the bandwidth
contiguous throughout the network, the maximum bandwidth of the concatenated
pipe is limited to that of the highest SONET rate commercially available today, OC-192/
STS-192. In the future, these rates could reach OC-768/STS-768 or higher. Additionally,
SONET contiguous concatenation cannot be done across SPEs that are on different
SONET line signals. These constraints can result in stranded bandwidth. Figure 10.
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