Subject: [AVT] Multicasting real-time traffic

From: "Flaks, Jason" <[email-masked]>
Date: Thu, 16 May 2002 09:55:31 -0700

Hello,

I am trying to send RTP data to a multicast address and am having some
problems.  I have three machines hooked together as a peer-to-peer (ad-hoc)
802.11 network, and I seem to have problems getting all the machines to
acknowledge each other.  There are no issues with unicast, and I am pretty
sure it is not my code.

Someone suggested to me that there are issues sending multicast packets that
exceed 1514 bytes.  Is this true?  Because the Dolby Digital RTP packets are
exceeding this at the moment.  Are there any other reasons I may be having
problems that are protocol related?

Thank you,
Jason

Jason Flaks
Technology strategy - Home networking
Dolby Laboratories
100 Potrero Ave
San Francisco, CA 94103
P: 415-558-0373
F: 415-863-1373

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From: Paul Stewart <[email-masked]>
Date: Thu, 16 May 2002 10:38:28 PDT

In message <[email-masked]> you write:
>I am trying to send RTP data to a multicast address and am having so
>me problems.  I have three machines hooked together as a peer-to-peer
>(ad-hoc) 802.11 network, and I seem to have problems getting all the
>machines to acknowledge each other.  There are no issues with unicast,
>and I am pretty sure it is not my code.
>
>Someone suggested to me that there are issues sending multicast 
>packets that exceed 1514 bytes.  Is this true?  Because the Dolby
>Digital RTP packets are exceeding this at the moment.  Are there any
>other reasons I may be having problems that are protocol related?

We've multicasted large frames (~40k at times) over 802.11b with 
moderate success, even in infrastructure mode.  If anything, ad-hoc 
mode should be easier.  We've seen problems with Windows CE 
receiving these multicasts, most likely an issue with fragment 
reassembly.  Some indication of what platform you're doing this under 
would be helpful.

--
Paul