(This Annex forms an integral part of this Recommendation)
This Annex Describes the use of the different progress indicator values defined in 4.5.22. Examples of use are given.
- Progress indicator No. 1 -Indicates that interworking with a non-ISDN has occurred within the network or networks through which the call has traversed.
- Progress indicator No. 2 - Indicates that the destination user is not ISDN.
- Progress indicator No. 3 - Indicates that the origination user is not ISDN.
- Progress indicator No. 4 -Indicates that a call which had left the ISDN has returned to the ISDN at the same point it had left due to redirection within the non-ISDN. This progress indicator would be employed when a prior Q.931 message resulted in a progress indicator No. 1 (call is not end-to-end ISDN), being delivered to the calling user.
The use of progress indicators Nos. 1, 2 and 3 is exemplified in the following.
Three interworking situations are identified in the Figure below:
a) interworking with another network;
b) interworking with a non-ISDN user connected to ISDN;
c) interworking with non-ISDN equipment within the calling or called user's premises.
d) interworking with another network behind the T reference point.
Figure G.1/Q.931
As regards calls from A the following applies:
case a) - progress indicator No. 1 sent to A;
case b) - progress indicator No. 2 sent to A;
case c) - progress indicator No. 2 sent to A (location sub-field = private network);
case d) – progress indicator No. 1 sent to A (location sub-field = private network).
As regards calls towards A the following applies:
case a) - progress indicator No. 1 sent to A;
case b) - progress indicator No. 3 sent to A;
case c) - progress indicator No. 3 sent to A (location sub-field = private network);
case d) – progress indicator No. 1 sent to A (location sub-field = private network).
The use of progress indicator No. 4 is exemplified in the following scenarios associated with the Call Forwarding supplementary service. If a call is originated from user A to user B, then as stated above, in the interworking cases b) and c) (see figure), Progress indicator No. 2 shall be sent to user A to indicate that interworking has occurred. If subsequently the call is forwarded from user B to user C, and user C is an ISDN user, progress indicator No. 4 shall be sent to user A.
The use of progress indicator No. 8, in-band information or appropriate pattern now available, is described in clause 5.