ip.access RTP setup details

Harald Welte laforge at gnumonks.org
Tue Jul 28 20:40:20 CEST 2009


Hi!

While writing the RTP proxy, I've been playing with the ip.access RTP related
code for quite a bit.  This is as far as I have understood it so far:

Setting up a voice call (for one MS)
 * sending IPACCESS_BIND via RSL, specifying
  * the GSM channel number IE
  * the IP speech mode IE, indicating
   * 0x1- : uni-directional, rx-only
   * 0x-1 : EFR (0: FR, 2: AMR)
 * receiving IPACCESS_BIND_ACK via RSL, specifying
  * the GSM channel number IE
  * the ip.access connection identifier
  * the locally-bound UDP port for RTP
  * the locally-bound IP address for RTP
  * optionally: the RTP payload type 
 * sending IPACCESS_CONNECT via RSL, specifying
  * the GSM channel number IE
  * the ip.access connection identifier (from BIND_ACK)
  * the remote UDP port number for RTP
  * the remote IP address for RTP
  * the IP speech mode IE, indicating
   * 0x0-: bi-directional
   * 0x-1: EFR (0: FR, 2: AMR)
  * optionally: the RTP payload type, if BIND_CAK specified it

Misc observations:
* if BIND is called with IP speech mode IE 0x10 (uni-directional FR), then no
  RTP payload type is returned in BIND_ACK.  Instead, the standard type for GSM
  06.10 (0x03) is used in the packets.
* I'm not sure which RTP payload type (and IP speech mode) is which, i.e. if
  the payload type of BIND/BIND_ACK specifies "expect this payload type for
  incoming packets" or "use this payload type for all RTP packets originated by
  this side"

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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