[Asterisk-Dev] help needed implementing H324M (UMTS Video)
Klaus Darilion
klaus.mailinglists at pernau.at
Wed Mar 30 08:32:28 MST 2005
Hi all!
I just wanted to inform possible developers that I made a page at
voip-info.org as starting point for further development.
http://www.voip-info.org/tiki-index.php?page=Asterisk+H324M
regards,
Klaus
> -------- Original Message --------
> Subject: [Asterisk-Dev] help needed implementing H324M (UMTS Video)
> Date: Thu, 13 Jan 2005 17:13:20 +0100
> From: Klaus Darilion <klaus.mailinglists at pernau.at>
> Reply-To: Asterisk Developers Mailing List <asterisk-dev at lists.digium.com>
> To: 'asterisk-dev at lists.digium.com' <asterisk-dev at lists.digium.com>
>
> Hi all!
>
> I investigae implementing a UMTS Video <-> SIP Video gateway in
> astersik. Currently I'm analyzing the asterisk code and reading the
> specifications (H.324M, H.223). I have several questions how to
> incorporate this into asterisk and hope that some of you can give me
> some answers. (If someone is already working on this, I would be happy
> to work with you)
>
> First, I will give a very short introduction into H.324M. H.324M is
> basically the same as H.324 with some adaptions for mobile terminals -
> it uses the mobile levels of H.223 for better frame detection and error
> recovery. In case of ISDN, the setup procedure is similar to an audio
> call, except the "User information layer 1": (btw: the debug output of
> asterisk is wrong - it should be "H.324M" instead of "G.7xx 384k Video")
>
> < Bearer Capability (len= 3)
> Ext: 1 Q.931 Std: 0 Info transfer capability:
> Unrestricted digital information (8)
> Ext: 1 Trans mode/rate: 64kbps, circuit-mode (16)
> Ext: 1 User information layer 1: G.7xx 384k Video (38)
>
> After the channel is established, the setup procedure will proceed in
> the established B-channel. H.223 will be used to multiplex the various
> logical channels (audio, video, control) over the B-channel. One logical
> channel will be established implicitly for enabling call control using
> H.245. Depending on the mobile level of H.223, the H.223 packets will be
> delimited using HDLC flags (01111110) (mobile level 0), 16 bit flags
> (level 1), or more complex flags (level 2 and 3). (You can also find a
> good and short introduction at:
> http://www.dilithiumnetworks.com/news/Media%20Coverage/IEEE_Multimedia_04July.pdf)
>
> Immediately after establishing the B-channel, the 2 clients have to
> agree on a H.223 mobile level. Therefore they are consecutively sending
> the flags to indicate their mobile level capabillities. Simultaneously
> the clients are analyzing the received flags to identify the mobile
> level of the remote client. If the mobile levels differ, the clients
> have to fall back to a mobile level supported by both clients.
>
> And now my questions/problems.
>
> - Where should I implement this functionality? Should I write an
> application which does H.324 or should I modify the zaptel channel?
>
> - Up to now I wrote s small application which uses f=ast_read(chan); to
> read a frame from the B-channel and later dumps the data to a file (for
> analyzing the received bit stream). Is there a better way to retrieve
> the unmodified stream from the B-channel? Is the order of bytes/bits in
> f->data the same as received on the B-channel? (I'm currently having
> some byte sex and byte order problems).
>
> I'm willing to put effort in this gateway, but somehow I'm lost in the
> source code and help by some experts will help me to focus on the real
> problems. Btw: Is there a developer guide which describes the design of
> asterisk and the usage of zaptel?
>
> Any help is greatly appreciated.
> regards,
> Klaus
>
>
>
>
>
>
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