INTERNATIONAL  TELECOMMUNICATION  UNION

		     ITU-T RECOMMENDATION SUMMARY


Rec. No. : G.704

Title :	Synchronous frame structures used at primary and secondary 
	hierarchical levels

Study Group : XV - Transmission Systems and Equipment

Version : Revised

Date of adoption : 1991

Notes :	


Recommendation G.704 gives functional characteristics of interfaces 
associated with:

	-   network nodes, in particular, synchronous digital 
	    multiplex equipment and digital exchanges in IDNs for 
	    telephony and ISDNs, and

	-   PCM multiplexing equipment.

A first section deals with basic frame structures, including details 
of frame length, frame alignment signals, cyclic redundancy check 
(CRC) procedures and other basic information.

Recommendation G.704 contains also more specific information about 
how certain channels at 64 kbit/s and at other bit rates are 
accomodated within the basic frame structures.

Electrical characteristics for these interfaces are defined in 
Recommendation G.703.

Note 1 - Recommendation G.704 does not necessarily apply to those 
cases where the signals that cross the interfaces are devoted to 
non-switched connections, such as those for the transport of encoded 
wideband signals (e.g. broadcast TV signals or multiplexed 
sound-programme signals which need not be individually routed via the 
ISDN).

Note 2 - The frame structures recommended in Recommendation G.704 
do not apply to certain maintenance signals, such as the all 1s 
signals transmitted during fault conditions or other signals 
transmitted during out-of-service conditions.

Note 3 - Frame structures associated with digital multiplexing 
equipments using justification are covered in each corresponding 
equipment Recommendation.



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