Page 108 - Optical Switching And Networking Handbook

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Synchronous Digital Hierarchy 93

1
Figure 4-6 Virtual Container 4
Creating a VC4 2
1 2 3
3

or:
E4/T4 Virtual Container 4

C 4
C4

When VC4 is aligned into an SDH frame, it becomes AU group 4
(AUG4) and is carried through the system. Figure 4-7 show this unit
aligned to the SDH framing format of an E-4 rate of 139.364 Mbps
inside a 155.52-Mbps framed SDH transport (STM-1).
One can see that the rates of multiplexing are very similar to the
SONET specification; however, differences in bit stuffing and clock-
ing still exist inside this framing and formatting. The comparison
now turns to the look and feel of SONET tributary multiplexing and
SDH multiplexing in the overall scheme of this transport system.
Figure 4-8 is a representation of a SONET multiplexing arrange-
ment used to produce AUG3 (which by all stretches of the imagina-
tion is T-3 or the seven T-2s). Here, the AUG is the equivalent of three
AU3s. One can now derive the fact that the three AUs creating the
AUG is an OC-3 operating at 155.52 Mbps.

Virtual Container 4 Administrative Unit 4
Figure 4-7
1 2 3 1 2 3
The E-4 is created
inside an STM-1.