[Asterisk-Dev] help needed implementing H324M (UMTS Video)

[Klaus Darilion]

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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