code being sacrificed in the course of the OmsoNITB split-up

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Neels Hofmeyr nhofmeyr at sysmocom.de
Mon Jul 24 14:45:02 UTC 2017


On Fri, Jul 21, 2017 at 08:42:38AM +0200, Harald Welte wrote:
> my suggestion here would be a set of optional, vendor-specific TLVs that
> we can introduce in the A interface to convey related information.

> Would be easy to include information about the actual physical channel
> from BSC -> MSC, such as BTS number (maybe CGI=MCC+MNC+LAC+CID), ARFCN,
> timeslot/sub-slot (rsl chan_nr)...
> 
> This is generally useful for all kinds of debugging.
> 
> In a similar manner I would tranasport some kind of subscriber
> name/identification from the MSC to the BSC so the BSC can still show
> who has allocated a given channel.  In its most generic form it could be
> as simple as a string TLV that the MSC can add to whatever downlink A
> interface message, and which the BSC accepts in every such message to
> talloc_replace_string() a field in its lchan, which can then be printed
> by various code (particularly logging) or used as log filter, or
> whatever else.

Agreed.

For the code review this means: we cannot sensibly add those kinds of TLVs
before we actually have the A-interface in the MSC. So the MSCSPLIT stage of
the code review in osmo-msc.git will drop the code and we shall re-add once we
have osmocom-specific TLVs added to our A-interface code. I tend towards
leaving the '#if BEFORE_MSCSPLIT' markings there to disable the code instead of
dropping it, to be able to easily find it later and see what it was supposed to
do.

> > - Add Osmocom specific TLVs to SMPP
> 
> Could be handled the same way, but should be yet another option, as it
> adds a lot of verbosity to the A interface which it otherwise doesn't
> need.  Not the highest priority, but definitely doable with reasonable
> effort.

I notice that this uses lchan measurement reports... not sure whether / when we
want to send those to the MSC, but am not familiar enough.
OS#2390

> > - Siemens BS11 MRPCI
> this has to be moved  to the BSC.

OS#2389 -- also makes sense to drop in initial split and re-add in osmo-bsc
after AoIP.

> > - In libmsc, gsm_04_08.c, we connect libbsc handle_abisip_signal(); the same is
> >   done in osmo_bsc_audio.c in osmo_bsc_audio_init(), so I assume it can be
> >   dropped from libmsc.
> 
> well, who are the usrers of the signal?

OsmoMSC no longer has an Abis interface, so it does not make sense to handle
that signal. Anyway, in osmo-nitb, the consumer was handle_abisip_signal() in
gsm_04_08.c, which apparently does RTP stream handling:
- receives S_ABISIP_CRCX_ACK to connect an RTP socket; and flush pending pending
  tch_recv_mncc requests (which I don't fully understand, guess it's RTP also
  stream related)
- receives S_ABISIP_DLCX_IND and frees an RTP socket.
Since RTP is now handled via osmo-bsc_mgcp, I conclude that this is indeed
obsolete.

~N
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