Subject: Re: [AVT] Multicasting real-time traffic

From: [email-masked]
Date: Fri, 17 May 2002 09:16:25 -0500

Hi Paul,

It seems to me that 802.11b does not have a native mode supporting 
multicast. You could use either broadcast mode or spy mode to fake a 
multicast. Is this the way you did with multicast over 802.11b? or, 
something I have missed?

Stan

Paul Stewart <[email-masked]>
Sent by: [email-masked]
05/16/02 01:38 PM
Please respond to stewart

        To:     "Flaks, Jason" <[email-masked]>
        cc:     "[email-masked]'" <[email-masked]>
(bcc: qiong-stan li/BRQ/RESEARCH/PHILIPS)
        Subject:        Re: [AVT] Multicasting real-time traffic
        Classification: 

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.

---

From: Paul Stewart <[email-masked]>
Date: Fri, 17 May 2002 12:23:12 PDT

In message <[email-masked]> you wr
>multicast. Is this the way you did with multicast over 802.11b? or, 

"Native mode supporting multicast"?  I really don't understand the
comment, especially with respect to the protocol 802.11b itself, as 
opposed to a specific hardware implementation.  If a frame is 
addressed to a multicast MAC address, it's a multicast.  I'm not sure 
where "broadcast mode" and "spy mode" get into it.  There are 802.11 
chipsets that implement multicast receive lists and promiscuous mode 
in exactly the same manner as 802.3 (ethernet) controllers do.

--
Paul

>--=_alternative 004EFDFF85256BBC_=
>Content-Type: text/html; charset="us-ascii"
>
>
><br><font size=2 face="sans-serif">Hi Paul,</font>
><br>
><br><font size=2 face="sans-serif">It seems to me that 802.11b does 
>not have a native mode supporting multicast. You could use either br
>oadcast mode or spy mode to fake a multicast. Is this the way you di
>d with multicast over 802.11b? or, something I have missed?</font>
><br>
><br><font size=2 face="sans-serif">Stan<br>
><br>
></font>
><br>
><br>
><br>
><table width=100%>
><tr valign=top>
><td>
><td><font size=1 face="sans-serif"><b>Paul Stewart &lt;stewart@parc.
>xerox.com&gt;</b></font>
><br><font size=1 face="sans-serif">Sent by: [email-masked]</font
>>
><p><font size=1 face="sans-serif">05/16/02 01:38 PM</font>
><br><font size=1 face="sans-serif">Please respond to stewart</font>
><br>
><td><font size=1 face="Arial">&nbsp; &nbsp; &nbsp; &nbsp; </font>
><br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; To: &
>nbsp; &nbsp; &nbsp; &nbsp;&quot;Flaks, Jason&quot; &lt;[email-masked]
>&gt;</font>
><br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; cc: &
>nbsp; &nbsp; &nbsp; &nbsp;&quot;[email-masked]'&quot; &lt;[email-masked]
>g&gt;<br>
>(bcc: qiong-stan li/BRQ/RESEARCH/PHILIPS)</font>
><br><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; Subje
>ct: &nbsp; &nbsp; &nbsp; &nbsp;Re: [AVT] Multicasting real-time traf
>fic</font>
><p><font size=1 face="sans-serif">&nbsp; &nbsp; &nbsp; &nbsp; Classi
>fication: &nbsp; &nbsp; &nbsp; &nbsp;</font>
><br></table>
><br>
><br>
><br><font size=2 face="Courier New">In message &lt;DFF1DE9BFABDD211A
>[email-masked]&gt; you write:<br>
>&gt;I am trying to send RTP data to a multicast address and am havin
>g so<br>
>&gt;me problems. &nbsp;I have three machines hooked together as a pe
>er-to-peer<br>
>&gt;(ad-hoc) 802.11 network, and I seem to have problems getting all
> the<br>
>&gt;machines to acknowledge each other. &nbsp;There are no issues wi
>th unicast,<br>
>&gt;and I am pretty sure it is not my code.<br>
>&gt;<br>
>&gt;Someone suggested to me that there are issues sending multicast 
><br>
>&gt;packets that exceed 1514 bytes. &nbsp;Is this true? &nbsp;Becaus
>e the Dolby<br>
>&gt;Digital RTP packets are exceeding this at the moment. &nbsp;Are 
>there any<br>
>&gt;other reasons I may be having problems that are protocol related
>?<br>
><br>
>We've multicasted large frames (~40k at times) over 802.11b with <br
>>
>moderate success, even in infrastructure mode. &nbsp;If anything, ad
>-hoc <br>
>mode should be easier. &nbsp;We've seen problems with Windows CE <br
>>
>receiving these multicasts, most likely an issue with fragment <br>
>reassembly. &nbsp;Some indication of what platform you're doing this
> under <br>
>would be helpful.<br>
><br>
><br>
><br>
><br>
></font>
><br>
><br>
>--=_alternative 004EFDFF85256BBC_=--

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