Le jeudi 08 février 2007 à 11:16 +0100, Richard Bennett a écrit : > > 2/ For ISDN network (Q.931 signaling), use of the UserInfo field, on the > > signaling session (yes, you can send some byte when the phone is > > ringing, without charge) > Ok... Are you sure you don't mean the 'Display' field in the ISDN SETUP > message? I can't find references to a UserInfo field in q931. > http://www.cotse.com/CIE/Topics/126.htm
Yes, this is the DISPLAY (sorry for the confusion, INFORMATION is a message itself). > Apparently the Q.931 protocol limits the maximum length of the Display Field > information element to 44 octets, that should mean one can use 44 characters > for a message without opening the line, which would be fine. ITU spec say 2 bytes minimum, up to 34 or 82 bytes, depending of the network (should be national specific ?) > It seems that GSM should support the full range of ISDN messages, > http://kbs.cs.tu-berlin.de/~jutta/gsm/js-intro.html > so I'm wondering, why is no one using this for enhanced caller-ID, or similar > applications. Where's the catch? I was working on a project, maybe 15 years ago, where we developped a "modem" to transfer data : 1/ during setup, for free 2/ during the blanks of a conversation (approx 80% of the time, because only one speaks at time, so you got a free 64kbps channel :)) This takes not very long until telco notice the D channel trafic, and since then, they charge for alerting, even if no answer (maybe 10% of unanswered call) to cover this trafic costs. Not sure about now, if this still a used (i'm not working anymore on low level communications). So, second part was to cut additional messages (SETUP DISPLAY) between network (aka roaming or international call). This need a more deeper test, but IMOO, this *could* be working on some networks, and probably not on some other. Now, about GSM networks and Gateways, I really dont know if this is a 1:1 passtrough .. --Alexandre _______________________________________________ OpenMoko community mailing list [email protected] https://lists.openmoko.org/mailman/listinfo/community
