Based on my understanding an STM-1 is 155 Mbits/s SDH pipe. At a high level PDH transmission systems can be mapped onto an STM-1 payload. The overall standard is based on the CCITT recommendation G.709.<br>
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A simple mapping can be 4 34 Mbits/s onto a 139/140 PDH, and 1 140 Mbit/s mapped onto an STM-1 payload, or a standards based soloution of 3x34 Mbit/s payloads mapped onto an STM-1.<br>
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Actual mapping is a little more complex.<br>
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