影音翻译

Preface
Referring to ITU-T G.703 (10/98), G.704 (10/98), G.706 (1991), G.823 (02/00), G.825 (03/00),
G.775 (10/98), G.824 (03/00), K.41 (05/98) and I.431 (03/93), this standard makes revisions on
GB 7611—1987 Parameters of digital interface for PCM systems over telecommunication
network, mainly including:
—Change the standard name into “Characteristics of the Electrical Interface at Hierarchical
Bit Rate for Digital Network”;
—Make revisions on the sketch map of interfaces, and define the names of interfaces
according to the function of interfaces in network;
—Make revisions on technical requirements for jitter and drift of interface;
—Make revisions on requirements for grounding of outer conductor of coaxial transmission
line or shielding layer of symmetrical pair which is in the connecting part between output port and
input port;
—Add requirements for surging safeguards against excessive pressure at interface;
—Add requirements for anti-interference capacity;
—Add requirements for balance to ground of 2,048kbit/s symmetrical interface;
—Add specification of 2,048kbit/s frame interface about Cyclic Redundancy Check
(CRC-4);