This Recommendation provides the recommended physical and electrical characteristics of the interfaces at hierarchical bit rates as described in [ITU-T G.702] (PDH) and [ITU-T G.707] (SDH), to enable the interconnection of digital network components (digital sections, multiplex equipment, exchanges) to form an international digital link or connection. The characteristics given in this Recommendation should be applied to new equipment (component) designs.

NOTE 1 – The characteristics of interfaces at non-hierarchical bit rates, except n 64 kbit/s interfaces conveyed by 1544 kbit/s or 2048 kbit/s interfaces and 3152 kbit/s interface in North American hierarchy, are specified in the respective equipment Recommendations.

NOTE 2 – The jitter specifications contained in this Recommendation are intended to be imposed at international interconnection points.

NOTE 3 – The interfaces described in clauses 5 to 12 correspond to the ports T (output port) and T' (input port) as recommended for interconnection in [b-ITU-R F.596-1] (Interconnection of digital radio-relay systems).

NOTE 4 – For signals with bit rates of n x 64 kbit/s (n = 2 to 31) which are routed through multiplexing equipment specified for the 2048 kbit/s hierarchy, the interface shall have the same physical/electrical characteristics as those for the 2048 kbit/s interface specified in clause 9. For signals with bit rates of n x 64 kbit/s (n = 2 to 23) which are routed through multiplexing equipment specified for the 1544 kbit/s hierarchy, the interface shall have the same physical/electrical characteristics as those for the 1544 kbit/s interface specified in clause 5.

NOTE 5 – The specifications contained in this Recommendation are related to the physical interface only (i.e., to characterize the line codes and input/output equipment interfaces); in particular, the required frequency tolerances do not imply overall equipment performances which may be driven by tighter requirements in Recommendations for specific network/equipment applications (e.g., [ITU-T G.813] and [b-ITU-T G.783]).

NOTE 6 – When measuring the performance of the output port described in clauses 6.2.1.2, 11.2, 12.2, 13.2, 14.2, 15.2, 17.2, 18.2, and 20.2, the signal attenuation, signal distortion, and length of the cable should be as small as possible. The length of the cable used could be chosen to be less than three meters, for example.