Hi David,
hope you don't mind me Cc'in the list, as other people might find this
information useful.
On Tue, Feb 17, 2009 at 08:31:53PM -0800, David A. Burgess wrote:
> Congratulations!!
thanks!
> So if you need the channel mode modify, does that mean you're doing very
> early assignment?
yes, it is the most simple option. commit the TCH early and you don't have to
do conflict resolval in the middle of the call setup if you first only have a
SDCCH and then want to switch to a TCH but don't have a free one.
> It took me a few days to figure that out when I decided to try very early
> assignment.
I was pretty clear that I have to do CHANNEL MODE MODIFY on GSM 04.08 to tell
the MS to switch to voice mode.
However, what is a bit weird is that in addition you have to send a MODE MODIFY
REQUEST (08.58) packet to the BTS. Plus, the actual channel mode values for
EFR are different on 04.08 and 08.58 ;)
Why is it weird? Because typically in a case like this, you would send one
08.58 packet to the BTS, with the payload for the 04.08 packet. The BTS would
then do the local state change, and send the 04.08 packet over the air to cause
the MS state change. This is how it works with many other operations, you
almost never have to explicitly talk to both sides separately.
> For early or late assignment, started call setup on the SDCCH, I didn't
> need that channel mode modify step.
I was aware of that, but then you need another channel assignment and a more
complex resource management, at least that's what I think. So I went for very
early assingment for now.
> Are you transcoding, or just copying raw vocoder frames from TCH to TCH?
No, I'm not transcoding. But in order to route TRAU frames from one TCH to the
other, you already need to do quite a bit of parsing and re-encoding. It's
just how they stuff the bits in the TRAU frames, not actually touching any of
the voice processing.
I think what is useful is to 'outsource' this TRAU frame processing into a
separate process. Apart from simple commands like 'map this sub-channel to
another sub-channel' it doesn't need much interaction with the actual
signalling part. In fact, the relatively high data rates clog the debug log
and make it hard to strace OpenBSC for further work on the signalling side.
On the ip.access nanoBTS it's even easier. You can directly feed the RTP
streams over the loopback device on the BTS, so the voice data naver even has
to go to the BTS (unless you want to route between multiple BTS, which I haven't
done yet but is very easy with nanoBTS too, in fact the code _should_ already
work.
What will be interesting is to figure out the actual RTP payload of the
ip.access. I've already seen they use RTP payload type 127 and the size of the
packets looks like it is one 40-byte TRAU frame per RTP packet. If that is
true, I would probably work on E1-to-RTP interworking to route calls between
traditional E1-based BTS and IP-based ones.
Cheers,
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Hi,
it seems that the last few commits (starting with SVN revision 308)
broke the compilation of bs11_config. As I wanted to take a look at
the boot process of my newly delivered BS11, I've just fixed bs11_config
to build again and it even seems to work.
Find attached my (ugly) patch to fix the build problems.
Regards,
Michael
--
Michael Gernoth Department of Computer Science IV
Martensstrasse 1 D-91058 Erlangen Germany University of Erlangen-Nuremberg
http://www4.informatik.uni-erlangen.de/~gernoth/
Hi all!
Like I just wrot in my blog, I have managed to get the first voice calls
between two MS on one BTS working. The Q.931 like call control never
really was the problem, and paging as well as RR/MM seems to work very stable
all the time. Bigger problems were related to the CHANNEL MODIFY that has
to be done on the 04.08 level (for the MS side) as well as the 08.58 side for
the BTS side - plus many classic programming mistakes in what used to be
so-far untested/unused code.
In any case, I have succesfully had voice calls through both the BS-11
as well as the ip.access nanoBTS.
There are still lots of things left to be done (e.g. the E1 subslot assignments
are still static, there is a big yet-to-be-explained lag on E1 based calls,
Motorola phones seem to have compatibility issues, you can call yourself and
make your own phone ring, etc). But at least the foundation is working.
Regards,
[... and it's not even two months too late for the originally planned call demo
at 25C3]
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Hi Philippe!
On Fri, Feb 13, 2009 at 03:31:08PM +0100, Philippe Langlois wrote:
> Can you also upload there some raw packet traces of this ip.access
> abis-over-ip ?
I'm working on a wireshark plugin, and I'll release traces + the plugin soon.
The traces will then be traces of OpenBSC talking to the nanoBTS. The traces
I currently have are from a test network, but contain things like IMSI/IMEI
numbers which I consider confidential information.
By the way: There is currently no wireshark plugin for GSM 12.21 (OML) yet, as
far as I can tell. Only 08.58 is there. Anyone interested in working on this?
Regards,
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Hi!
I've started a page documenting the ip.access A-bis over IP protocol at
https://bs11-abis.gnumonks.org/trac/wiki/nanoBTS
There are no NDA problems with it, since all information was derived from
looking at packet traces. I do not have access to any protocol documentation
from ip.access.
Regards,
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Hi!
This seems to solve the mystery that zecke and me experienced yesterday
working with the B-Channels on mISDN.
Regards,
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
Hello Bjoern,
> Can't get logged in to the LMT.
> It asks for a password (cambio menu).
> "L3proc" isn't working...
This is not the LMT COM Port, you have plugged the cable into
the wrong port. Besides the LMT COM port, which is close to the
E1 BNC connectors, there are several other COM ports which are
directly routed to the various microcontrollers. There are some
simple debug menues active during startup, but on the LMT port
you won't get any reply without sending the correct message first.
Best regards,
Dieter
--
Dieter Spaar, Germany spaar(a)mirider.augusta.de
Hi!
I was trying to get the data model right for the TRAU mux/demux handling,
and discovered it is about time to re-do the entire 'input' side, i.e.
the interface towards the actual E1 link.
The main objectives are:
1) ability to deal with multiple BTS on one E1 link
2) ability to easily integrate E1 drivers != mISDN, e.g. zaptel while
still keeping most of the E1 related functionality in common code
3) ability to easily add things like Abis over IP later
So please stay tuned for some potentially quite big committs in that area during
the next couple of days.
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
