Multiplexing E1/T1 Channels To Form Stm-1; Calculating E1/T1 Channel Sequence Numbers - 3Com MSR 50 Series Configuration Manual

Multiplexing E1/T1
Channels to Form STM-1
Calculating E1/T1
Channel Sequence
Numbers
Administrative unit (AU) and administrative unit group (AUG): AU is the
■
information structure that provides adaptation between higher-order channel
layer and multiplex section layer. AUG is a set of one or more AUs that have
fixed location in the payload of STM-N.
In SDH multiplexing recommended by G.709, there are more than one path for a
valid payload to be multiplexed to form STM-N. The following figure illustrates the
multiplexing process from E1 and T1 to STM-1.
Figure 151 Process of multiplexing E1 channels to form STM-1
x 1 x 1
STM-1 AUG-1 AU-4
x 3
Multiplexing
AU-3
Mapping
Aligning
Figure 152 Process of multiplexing T1 channels to form STM-1
x 1 x 1
STM-1 AUG-1
x 3
Multiplexing
Mapping
Aligning
In actual applications, different countries and regions may adopt different
multiplexing structures. To ensure interoperability, the multiplex mode command
is provided on CPOS interfaces. This allows you to select the AU-3 or AU-4
multiplexing structure.
Since CPOS interfaces adopt the byte interleaved multiplexing mode, the
lower-order VCs are not arranged in order in a higher-order VC. To understand
how TU numbers are calculated, see the following example where E1 channels are
multiplexed to form STM-1 through the AU-4.
As shown in Figure 151, when the AU-4 path is used, the multiplexing structure
for 2 Mbps is 3-7-3. The formula for calculating the TU-12 sequence numbers of
different locations in the same VC-4 is as follows:
Sequence number of TU-12 = TUG-3 number + (TUG-2 number - 1) x 3 + (TU-12
Number - 1) x 21
VC-4
x 3
TUG-3
x 7
VC-3
TUG-2 TU-12
x 7
x 3
AU-4 VC-4
x 3
TUG-3
x 7
AU-3 VC-3
TUG-2
x 7
Overview
C-12: 2.048 Mbps
VC-12 C-12
C-11: 1.544 Mbps
TU-11 VC-11
x 4
541
C-11