[streaming] Re: Multicast over wlan flooding the network

[Chhaya, Harshal]

> I'm experimenting with multicasting video over a WLAN network, using

There are two specific issues with multicast over a WLAN that
might be causing the problem:

1. Most APs send multicast/broadcast data at a lower rate
than unicast data. This is to make sure that everyone in
the network can successfully receive the packets. If your
video stream needs a higher bit-rate than supported by the
AP for multicast, you will lose packets.

Some APs allow setting the multicast rates to be the same
as unicast rates. Check if your AP allows this. This may
solve the problem.

Since you mentioned that your WLAN becomes really busy when
you stream the video, it could be that the video stream needs
all the available multicast bandwidth. Try transcoding the
stream to a lower rate and see if that works.

2. The other characteristic of multicast traffic over a WLAN
is that it is unacknowledged. Unicast data uses acknowledgements
on the protocol level and is is re-transmitted if there is any 
error and so is more reliable. Multicast data does not use these
acknowledgements and so is not re-transmitted even if there are
errors. If your wireless channel is not robust i.e. if there are
other WLAN networks close by or if you have other devices - 
cordless phones, even microwaves - that cause interference, you
will lose data due to errors but it will not be re-transmitted.
The result will be missing data and a choppy, unusable video stream.

The solution to this is to first try different channels and see
if they are 'cleaner'. 

If using unicast streaming is an option, be sure to use that.
That will solve both these problems. 

Regards,
- Harshal

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