The scope of this Technical Report extends to the So and S2 interfaces between DPEs and PSNs, as described in Technical Report ECMA TR/24. Only testing and maintenance of the interfaces Physical Layers and D-channel protocol functions are considered here. Other DPE and PSN functions are excluded, i.e. they are considered subjects of separate maintenance procedures. No assumption is made concerning the internal structure of each end of a connection. For reasons of symmetry, the two ends of a connection will only be differentiated by the part they play in maintenance operations, i.e. requesting or executing.
Emphasis is given to maintain (or at least diagnose) the functions in question not only locally but also remotely.
Maintenance of connections via intervening non-ISDN networks, i.e. involving Interworking Units (IWU) are beyond the scope of this Technical Report. However, they have been kept in mind to produce open ended solutions and not to preclude further studies on this topic.