PDH Network Elements

The inland management functionality enables the SDH network manager to receive information about the quality of service, the damaged elements (if there are any) and gives the manager the option to change the network configuration from a remote site. In order to be able to do the same things with the PDH network, one should build another separated network for the management and the remote control.

The ability to multiplex any of the standard bit rates into the STM-n frame is possible due to the complicated containers structure of the STM-n frame as depicted bellow.

PDH/SDH split over BT�s network

In order to map an E1 (2.048 Mbit/Sec) into the STM-n frame we have to create a TU-12 stream which is a low rate stream that is synchronized to the SDH network clock. The TU-12 is composed of the E1 data, indication bits, stuffing bits, management bits and a direct pointer to the E1 frame.

The TUG-2 is a structure that can be composed of 3 TU-12s (3 E1s), or 4 TU-11s (4 T1s), or 1 TU-2 (1 T2). This structure gives the STM frame its flexibility to multiplex different rates directly into the STM-n frame (impossible in the PDH protocol). The next stage is mapping 7 TUG-2s into 1 VC-3 or into 1 TUG-3 and so on according to the flow chart.

This method of multiplexing allow us to directly map the T1, T2, T3 (American standards) and the E1, E2, E3, E4 (European standards) into the STM-n frame.

Each time we map lower rate streams into a higher rate structure we add pointers to a fixed point in the lower rate streams, so we can directly extract the relevant information without demultiplexing the all high rate stream.

When stuffing is needed the pointer to the fixed location is changed according to the direction of the stuffing, this is the improvement of stuffing algorithm used in the PDH .