Some more thoughts on that old topic:
A custom protocol seems to make more and more sense. Neither original RSL nor 08.08 seem to be a close match.
Some more specification of the original protocol idea:
On Wed, Apr 14, 2010 at 11:48:22PM +0200, Harald Welte wrote:
- ESTABLISH REQUEST -- app requests a channel be established to MS (by IMSI)
Parameters: * mobile identity (tmsi/imsi) (can re-use 04.08 mobile identity IE) * channel type (sdcch/tch) (can reuse RSL information element) * which parts of the protocol shall openbsc handle (RR/MM/CC) * unique reference identifying this 'call/radio channel'
- ESTABLISH CONFIRM -- network confirms a channel has been established
(confirmation that the radio channel has been established) Parameters: * unique reference identifying this call/radio channel * exact arfcn/timeslot/sub-slot that was established (can be RSL or 04.08 channel description)
- ESTABLISH INDICATION -- network tells app connection was made by MS
(confirmation that a LAPDm connection was established) Parameters: * unique reference identifying this call/radio channel * SAPI (RSL Link ID)
- [UNIT] DATA REQUEST -- app requests data to be sent to MS
- [UNIT] DATA INDICATION -- network indicates data was received from MS
Parameters: * unique reference identifying this call/radio channel * SAPI (RSL Link ID)
- ERROR INDICATION -- network tells app something went wrong
Parameters: * unique reference identifying this call/radio channel * error code / reason
- RELEASE REQUEST -- app asks network to release channel
Parameters: * unique reference identifying this call/radio channel
- RELEASE CONFIRM -- net tells app that channel was released (as rqd)
Parameters: * unique reference identifying this call/radio channel
- RELEASE INDICATION -- net tells app that channel was released (by MS)
Parameters: * unique reference identifying this call/radio channel