2 May
2017
2 May
'17
12:45 p.m.
On Sat, Apr 29, 2017 at 12:28:10PM +0200, Andreas Mueller wrote:
Hello,
is it possible to connect the openbsc from the vlr_3G Branch with sip-connector to
asterisk as described on
https://osmocom.org/projects/osmo-sip-conector/wiki/Osmo-sip-connector, or are there
changes in the vlr_3G Branch that makes this impossible?
When trying to set this up I was able to call an UMTS-Phone which was connected to the
nano3G from a softphone using jitsi, and the UMTS-Phone was ringing, but it was not
possible to answer the call.
I have only limited experiences with asterisk and so I am for example unsure about what
voice-codecs to use, if my asterisk-config is correct,... and so I would like to know if
it should work in principle and I have to find the correct configuration.
So far the 3G has only been tested with a single femto cell, routing voice
back to the cell, there's almost certainly RTP streaming flexibility
missing there.
Personally I'm not very familiar with SIP and osmo-sip-connector, so I
can't tell you right away what the next steps would be. But we're also
working on a proper A-interface to the OsmoMSC, meaning that the way the
vlr_3G branch is using RTP will become the "normal" way Osmocom will
handle RTP streams (IIUC). In other words, we should soon reach the point
where me or others at sysmocom will actively be looking into RTP streams
and multiple cells and osmo-sip-connector.
If you'd like to go ahead on it, you could try to grok the MGCP
communication and osmo-bsc_mgcp redirecting the RTP streams, to see if
there's a simple stupidity you could patch up.
See openbsc/openbsc/src/libmsc/msc_ifaces.c, which instructs osmo-bsc_mgcp
to route the RTP stream with these functions:
conn_iu_rab_act_cs()
mgcp_response_rab_act_cs_crcx()
iu_rab_act_cs()
mgcp_bridge()
mgcp_response_bridge_mdcx()
And look at the osmo-bsc_mgcp log output to see the sequence of things.
Basically it creates echoing RTP endpoints for each subscriber by sending
'CRCX' MGCP commands to osmo-bsc_mgcp, and once both RABs are assigned,
calls 'MDCX' to connect those two RTP streams together.
As I said that's fairly barebones, just about working, and a lot needs to
be done to make it universally usable. Any help or analysis there would be
very welcome!
~N
--
- Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/
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