INTERNATIONAL  TELECOMMUNICATION  UNION

		     ITU-T RECOMMENDATION SUMMARY


Rec. No. : I.253.1

Title : Call waiting (CW) supplementary service

Study Group : I - Services

Version : Revised

Date of adoption : 1990

Notes :	


The Call Waiting service is a supplementary service which permits a 
subscriber to be notified of an incoming  call (as per basic call 
procedures) with an indication that no interface information channel 
is available. The user then has the choice of accepting, rejecting or 
ignoring the waiting call (as per basic call procedures).

The ISDN Call Waiting service allows an out-of-band notification to 
subscriber B of the incoming call; this is the assumed case for the 
definition.

The maximum number of calls that can be handled (e.g. active, held, 
alerting, waiting) for each ISDN number on a given interface is 
specified at subscription time.

Note - The situation where at least one B-channel is available may be, 
for a given terminal, a situation similar to the one where all 
B-channels are busy. A terminal receiving a call request and already 
having an active call, may process the new incoming call in the 
same way as it would have processed a call if no B-channel were 
available, i.e. react positively to the incoming call request.

Moreover, when at least one B-channel is free, any compatible busy 
terminal of subscriber B can react positively to an incoming call.



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