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Andreas Eversberg andreas at eversberg.euHarald Welte wrote: > I did some brainstorming with Peter and Holger about the idea to assign > all phones interested in listening to the audio stream to the same TCH / > timeslot on any given BTS. This is highly experimental and > non-standard, but I think we can make it work by using late assignment > and ignoring the 100% bit errors in uplink. hi harald, looks like voice broadcast service for phones that don't support it :) let me think about it... first the phone is assigned to SDCCH, so we get informations about dialed number (audio broadcast number). then the BSC triggers assignment to the "shared" TCH. now the phone suspends layer 2 connection on SDCCH locally and resumes layer 2 connection on the TCH, to send the assignment complete message. as we need to ignore the uplink (many phones can be assigned to the same TCH), we need to send one UA frame to make the phone think that we received the SABM frame, which we didn't. (hopefully the phone receives that UA frame.) also we need to send one or several RR frames to make the phone think that we received the ASSIGNMENT COMPLETE message, which we also didn't. we send more UA and RR frames when new phones join the shared TCH. this will result in small audio gaps, which might not be a real problem. this all works until a phone tries to hangup or sends a keypad message. the layer 2 would run into timeout, because there is no RR frame with increased sequence number that acknowledges the hangup or keypad message. i see no problems with timing advance, since we don't care about uplink. when we use a fixed TA value of 3 (ordered on SACCH), we do not get any problem with interference of next timeslot, as long as the phone's distance is not above about 3km. but i see a big problem with layer 2: if a phone receives another UA (because another phone joins the TCH), it would run into an MDL_ERROR (unsolicitated UA response), that causes the RR layer of the phone to abort the connection. i have no solution to prevent this (yet). this is why i think it will not work. regards, andreas