3.5. SONET/SDH Transparency Services
SONET and SDH have the following notions of transparency built-in, as described in Chapter 2:
Path transparency, as provided by the SONET line and SDH multiplex section layers. This was the original intent of SONET and SDH, that is, transport of path layer signals transparently between PTEs.
SONET line and SDH multiplex section transparency, as provided by the SONET section and SDH regenerator section layers, respectively.
SONET section and SDH regenerator section transparency, as provided by the physical layer.
Of these, only (1) was considered a “user service” within SONET and SDH. There are reasons now to consider (2) and (3) as services, in addition to newer transparency services.
Figure 3-8 shows a typical ...
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