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Re: [Discuss-gnuradio] The OpenBTS project - an open-source GSM basestat

From: David Burgess
Subject: Re: [Discuss-gnuradio] The OpenBTS project - an open-source GSM basestation using the USRP and VoIP
Date: Thu, 4 Sep 2008 09:56:18 -0700

Eric -

Here's what can be released now:

-- The GMSK radiomodem and its interface to the USRP. (GSM 05.01, 05.04, 05.05) -- The interface between the GMSK radiomodem and the rest of the GSM stack. -- The FEC coders and decoders used in GSM 05.03. (Already in CVS, BTW.)
        -- Most of the TMDA functions of GSM 05.02.
        -- Serializers and deserializers for L3 messages.  (GSM 04.08)
-- The hybrid GSM/SIP control layer. (GSM 04.08, ITU-T Q.931, IETF RFC-3261, IETF RFC-3550)
        -- An incomplete SMS stack.

What's missing:

-- Parts of the TDMA (GSM 05.02). This can all be done with tables and isn't that complex. -- The code to organize the FEC components into actual L1 channels (defined in GMS 05.03). This is straightforward, though, and we will publish some base-class examples. Once you have the framework in place, this stuff almost writes itself. -- GSM L2, LAPDm, is defined in GSM 04.06. It borrows heavily from ISDN LAPD (ITU-T Q.921). Both LAPDm and LAPD are subsets of HDLC. We will publish a initial .h object framework. There is also an open- source ISDN LAPD implementation that makes a useful reference. Our current LAPDm is less than 500 lines of code, so replacing it should not be a huge chore, especially with a .h object framework and example LAPD as a starting point.

I'm sorry to sound coy about this. It would simply not be prudent to release some of this code into the public right now and it might take over a year for that situation to be resolved. We don't want to wait another year so we're releasing what we can and hoping enough interested people get involved to replace what's missing.

-- David

On Sep 3, 2008, at 11:52 PM, Eric Blossom wrote:

By GSM layers 1 and 2, do you mean all of GSM 05.*? (or more or less?)

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David A. Burgess
Kestrel Signal Processing, Inc.

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