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94 Chapter 4

Multiplexed
Figure 4-8
The SONET
Administrative Unit 4
tributary
multiplexing
scheme

Administrative Unit Group

SDH - AU4 (E-3s or 1E-4)
Figure 4-9
The final outcome
of SDH or SONET
STM-N
framing
SONET OC-3
3 2 1

Finally, comparing the multiplexed rates into these AUGs in both
SDH and SONET, the outcome is STM-n, as shown in Figure 4-9.We
can add the services as necessary to get to STM-4, which is the
622.08-Mbps transport, or STM-16, which is the 2.488-Gbps trans-
port system. One can see that the two systems are very closely
aligned to each other; just different multiplexing and formatting
arrangements are used in defining the overall platforms.
Table 4-5 is a comparison of the combined services just described,
including the two systems: the electrical rates and the payloads.This
comparison also includes information regarding the overall frame
size. Looking at the table shows that industry standardization was
somewhat successful in getting the systems to align with each other
and prevent some of the age-old problems of the past.
Figure 4-10 shows the overall structure of VC multiplexing as a
graph in the flow of channels inside the overall STM-n as depicted by
ITU Standard G.707. This is a simple way to view the overall struc-
ture of the SDH multiplexing scheme.