[Live-devel] Multicast over Wireless LAN

[Tim Stabrawa]

#TAY KOON HWEE# wrote:
> Hi guys,
>  
> I have the following problem with multicasting. My program installed 
> in my PC is able to unicast to laptops/PDA connected wireless to my 
> router. However, for multicasting, it only works for devices connected 
> by LAN cable to my router. Therefore PDA will not be able to receive 
> the multicast while laptop if connected via LAN cable to the router 
> will be able to receive the multicast.
>  
> Weird thing is if my program installed on my laptop (wireless 
> connected to my router) is about to stream (unicast and multcast) to 
> devices connected by wires to the router.
>  
> Does the RTCP Bandwidth got to do with it? I have set my 
> estimatedSessionBandwidthVideo = 512.
>  
> Can anyone advise on the above problem?
>  

My best guess is that your router itself is at fault.  The way most 
switches work with multicast is they'll treat it as broadcast and flood 
the network.  (You'd have to shell out extra bucks to get one that 
handles it smarter - read up on GMRP (802.1p) if you care.)

Now, wireless routers on the other hand, tend to do something funky with 
how they connect up the wireless and wired clients.  For example, the 
Linksys WRT54G has physically separate interfaces to the main processor 
for wireless and wired clients.  It provides connectivity between the 
two with a software bridge (which effectively combines them as if they 
were connected via a hardware switch).  FWIW, it looks like multicast 
traffic is being forwarded to my wireless link on my WRT54G (only 
verified by looking at the LED's though).

Chances are your particular router is trying to be smart and is 
filtering multicast traffic from appearing on the wireless interface 
(presumably so it doesn't bog down the wireless link with useless 
data).  It's possible, although unlikely, that you can receive the data 
from your wireless device if you do a GMRP join procedure for the 
multicast session(s) you're interested in.  I've never done this in 
practice though, since I've never actually seen a switch that supports GMRP.

Anyways, hopefully some of this is useful or interesting.  It kept me 
amused writing it at least.  :-)

Good luck,

- Tim