This Recommendation covers the network node interface (NNI) specifications which are necessary to enable interconnection of network elements at their synchronous digital hierarchy (SDH) interfaces for the transport of different types of payloads.

Therefore, this Recommendation specifies:

– the bit rates for STM-N signals;

– the frames structures for STM-N signals;

– the formats for mapping and multiplexing of client signals (e.g., PDH, ATM and Ethernet) elements into an STM-N frame;

– the functionalities to be implemented in the different overheads of an STM-N frame;

at the NNI of a synchronous digital network, including B-ISDN.