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Nordin bouchtaoui at gmail.comHi Harald, I would love to contribute as much as I can, but as a father of two kids and as a husband it's really hard to have some time free. So my contribution is very minimal, sorry for that. All I can do is doing some tests, try to modify parameters in the source and give feedback about the result. And ofcourse learn as much as possible :) Anyway, I'll do everything I can to help you. Offtopic: Today I'm a bit sad, because Michael Jackson died. Thank you. Harald Welte schreef: > Hi! > > I've started to analyze GPRS and was actually even starting to write some code > for it, but then have given up for the time being - it's much more work than > anticipated. > > Given the long todo list of OpenBSC right now, I think I'll have put aside GPRS > for some time :( > > Based on looking at protocol traces, I have figured out the nanoBTS GPRS/EDGE > implementation roughly looks as follows: > > * make sure we allow the BTS to activate the GPRS software components > in abis_nm / OML activation! > * BTS will use a UDP connection on port 23000 for the GPRS related frames. > The GSM specs will consider this type of connection between the PCU (part > of the nanoBTS) and the SGSN. The establishment/configuration of the > UDP port number and SGSN ip address has not yet been identified. Probably > similar to how the RSL link is activated via OML. > > The protocol stack looks like: > > IP : UDP : NSIP : BSSGP : LLC : higher-layer > > IP and UDP you should know and/or not care about ;) > NSIP is a IP-enabled version of NS as specified in TS 08.16 > BSSGP is specified in TS 08.18 > LLC is as specified in TS 04.64 > > the higher-layer depends on the SAPI value of the LLC and can be > * GMM (GPRS Mobility Management as specified in 04.08) > * User Data (actual IP packets, e.g.) > * SMS > > So what is weird about this is that the GPRS MM is actually part of 04.08, but > it is not terminated at the BSC but rather at the SGSN. Also, the deep stack > comprised of many headers is really weird. Furthermore, it seems that a lot > of the packet scheduling and timeslot allocation is happening inside the > nanoBTS - very unlike the GSM side of things. > > I have not yet managed to figure out how to allocate/dedicate resources to > GPRS.. after all, the BTS needs to know how many timeslots it can use for it, > etc. > > If anyone wants to dig deeper, you're most welcome to do so. A list of > relevant specs: > > 01.61 GPRS cipher algorithm requirements > 03.60 Overall GRPS logical architecture (above RL and MAC) > 03.64 GPRS radio interface > 04.60 RLC/MAC on PDCH > 04.64 MS-SGSN LLC spec (on top of RLC/MAC) > 04.65 SGSN SNDCP > 08.14 BSS SGSN Gb Layer 1 > 08.16 BSS SGSN Gb Layer 2 > 08.18 BSS SGSN BSS GPRS protocol > 09.95 Interworking between modified PLMN supporting legacy GPRS and GPRS mobiles > 22.060 GPRS Service Spec > 23.060 GPRS Radio Service Spec > 29.016 SGSN - VLR Interface Gs network interface spec > 29.018 SGSN - VLR Interface Gs layer3 interface spec > 29.060 GPRS Tunneling (GTP) over Gn and Gp > > Happy hacking, >