In a structured mode, the service is also Point-to-Point and will have identical
TDM service handoffs on either end, except that the overhead and payload entering on
one end will terminate the overhead at the near endpoint and transport the payload
transparently to the other end where it is mapped to the same type of overhead and terminated.
Examples of this are typical OC-3 services where the SONET overhead (SOH)
is terminated locally and the payload transported and the overhead then added before
terminating at the other end. The CES will maintain the integrity of the transport.
Finally, in the multiplexed mode, multiple lower-rate transparent services are multiplexed
at a specific service endpoint on the network into a higher digital hierarchy.
Similarly, a higher rate service may be decomposed into several lower rate services.
For example, a customer may have several sites??”a head office with a full DS1 connection
and several satellites with fractional DS1 connections, as shown previously in
Figure 2.16. The same architecture can be used for multiplexing of other rate services,
for example, several full DS1 services onto a single DS3 or multiplexing of VT-1.
Pages:
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250