R2511-HP MSR Router Series Interface Configuration Guide(V5)

Figure 12 Process of multiplexing E1 channels to form STM-1

Figure 13 Process of multiplexing T1 channels to form STM-1

In actual applications, different countries and regions might 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.

Calculating E1/T1 channel sequence numbers

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 12, w

hen 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

The two TU-12s are adjacent to each other if they have the same TUG-3 number and TUG-2 number but

different TU-12 numbers with a difference of 1.

The numbers in the formula mentioned refer to the location numbers in a VC-4 frame. TUG-3 can be

numbered in the range of 1 to 3; TUG-2 in the range of 1 to 7 and TU-12 in the range of 1 to 3. TU-12

numbers indicate the order (E1 channel number) in which the 63 TU-12s in a VC-4 frame are multiplexed.

STM-1

TU-11TUG-2VC-3AU-3

TUG-3VC-4AU-4AUG-1

VC-11C-11

×1 ×1 ×3

×3

×7

×4

C-11: 1.544Mbps

Multiplexing

Mapping

Aligning