WiFi network setup for live video stream

[irilad]

Hi All,

Currently I have a setup using a 2.4 and 5Ghz dual band router with two SDI to IP video encoders attached to the same LAN.
I'm doing a UDP multicast of a 1.5 Mbps video version from the first encoder and an 8 Mbps encoded version from the second.

There are about 6 or 7 iPads with VLC app that receive the stream around the area of the router. The router is not great and I'm constrained by hardware I can use.

Users can connect to either the 2.4GHz or 5GHz SSID to receive either stream (they open the low bit rate multicast on 2.4 and the high bit rate multicast on 5).

It seems to work reasonably fine in testing but there have been reports of jumpy video at times.
Just wondering does this setup seem OK? I have the option to use RTSP multicast as alternative.

I'm not sure if multicast is flooding the router?

Thanks

 

[bill001g]

I would test watching on a wired connection to see if the feeds stall at the same time. It would give you a indication if the wireless is the cause.

I forget most the details but multicast over wifi is very special thing. If you were to send broadcast udp traffic the wifi would send a copy to each user using the unique session key for each person. Even though it is not required by the application the wireless chipsets will retransmit the data to avoid packet loss.

Multicast is run very differently. It uses a special key that all the clients know, this is part of they WPA/WPA2 key negotiation. It only transmits 1 copy of the data using a different encoding that tends to be more reliable and since it is sent out without any knowledge of which end clients are receiving it or if they got it successfully.

In theory at least it should take less resources on the router because it is not having encrypt the data for each user and give them each a copy.

Still the signal is susceptible to interference so it may be simple wireless interference causing the problem. This tends to be very hard to troubleshoot because even though multicast is supported by a lot of router many times you will not even see in mentioned in the documentation because the wireless chipset is doing all the work.

My normal method would be to run wireshark and capture the data to see if there was any pattern to the loss and if all machines were losing the same packets. There are sequence number in video feeds so it is pretty easy to see which data got lost. When you have IPADS i have no clue if you can even capture data.

Maybe you could run with no encryption and see if it makes any difference.

 

[irilad]

Hi Bill,

Thanks for your response..
I will do some more testing today and see how it goes.

The encoders have the option of either UDP multicast/unicast or RTSP multicast/unicast.
I wonder would RTSP be a better option? It seemed slightly more stable yesterday.

 

[bill001g]

I wish I remembered how RTSP worked in relationship to mulitcast. I thought it was a control stream that run on tcp while the data ran multicast.

If you use unicast the router will have to create a copy for each person it does not take long to kill a wifi point.

Still this might not be the same issue it used to be, the company I work for has gone to a different type of video distribution system that work more like a torrent where the end stations resend parts of the video to each other. Even though it must be sending much more data over the wifi it seems to work better......then again the problem in our case was not multicast itself it was getting the PIM to work correctly when you have lots of MPLS vendors in lots of countries, it worked fine in the lan once the multicast data got there.