Wireless streming to 150 tablets or monitors

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Aikiseeker

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I'm trying to design a classroom with monitors similar to the flight seats with inbuilt monitors. The monitors can take a video feed from the CCTV installed in the classroom and also from the Projector that is connected to the teacher's PC.

What hardware would I need and software for that matter.
 
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bill001g

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Wired is pretty easy it is a generally done with multicast and once of the many clients including Microsoft media player that can accept multicast traffic.

Wireless and I will assume you mean 802.11 type wireless and not tv broadcast is almost impossible. You of course could still use multicast since it is supported on wireless. The larger problem is that since this is a edge device every user will need to get a copy of the stream. Even a small 300k stream will kill your AP when you try to run 100+ users on it.
 
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Aikiseeker

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Thanks. But I plan on distributing the load across 6 APs from a single switch connected to the media server. So if I get it right, I'll be looking at streaming HD Cam into my media server and have that multicast over the network for the tablets to receive using a multicast client.

I believe the solution for the slides would be to have it as a stored file in the server for the tablets to access and run through independently to the lecturers. This way, the students have the flexibility of pausing or going back and forth the slides whilst the lecturer goes on and on...
 
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bill001g

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Your problem is not the number of AP it is the total radio bandwidth. The AP themselves normally support multicast and you would only send one feed to each AP so the uplink to the AP itself will only have the one copy of the traffic. If you worked at it really hard you could split your users into 6 different radio channels. This is a huge pain because you would have to manually assign SSID for the users to connect to to ensure even load.

You are still talking 25 users per AP sharing a single channel. If you could somehow only allow the AP to transmit it might work but I can't see how you avoid data collision and retransmission which is what greatly reduces the throughput of a AP when you have multiple users. You notice the manufactures only claim their 150m or 300m or whatever when they test between a wired user and a single wireless user.

I would run this as a non encrypted system to reduce the cpu load on the AP since it would have to encrypt 25 copies of the stream. Its too bad there was not a wireless sniffer program that could capture the data out of the air and play it back. You would only need a single AP and single video feed.
 
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bill001g

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So after some more reading on how multicast works on AP it appears I am incorrect.

It does appear that multicast packets are actually sent out over the radio itself only 1 time and the clients can all share the same exact packets. This would mean it is more effective to use only a single AP to do this. Of course the AP need to be able to a tolerate that many sessions in its memoery tables but since the clients send only IGMP keep alive message the traffic should be minimal. This assumes the end devices are not allowed to send other data and eat up bandwidth.

I would still recommend a open system but it does appear WPA2 solves even this problem if you need the multicast encrypted. From what I read there is a special key generated called a GTK key that is used to decrypt these multicast messages. Unlike the session keys each user is using for their connection the GTK is the same for all users so anyone who has a valid session will have this key and can decrypt the multicast. The only down side I have seen is the GTK key is recalculated and sent out to the client every time someone disconnects. This you would think would impact video streaming traffic if you had lots of machine going on and off the AP.

I now am going to have to get my wireless sniffer setup again and see what multicast traffic really looks like.
 
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Aikiseeker

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OK, that sounds more appealing. I'm sorting out all inputs and so far my concept design would be.

Surface RT's for the tablet. Since they are pretty darn cheap for a windows touch tablet. And I'm not sure how to go about with an android device.

A PC acting as a media server and a separate NAS for the lecturer files, which would be mostly power point one would think.

The PC will attach to a switch which also connects to the various APs that would be configured as a single point.
2 HD IP cams would be attached to the switch and the PC will act as an NVR that would record and also live stream the video feed. The feed would be captured by the tablets via IP address using IE.

Or I'll look around for a dedicated streaming software. I'm not sure yet.
 
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bill001g

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Most times I use VLC to test with it is not nearly as nice as commercial stuff but for no cost it works well and it is one of the few that you can stream mulitcast with. I know a lot the commercial stuff like to use microsoft silverlight for the player. Mostly I deal with the issues of delivery of the multicast traffic to multiple location spread over the world I do not know exactly how they are generating the traffic. There are a bunch of competing platforms on the market and I know the one they selected for our company allows them to switch between live video and recorded video or screen presentations.
 
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Aikiseeker

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that's great, could you elaborate on your server side set up and how the media casting or selection occurs?
 
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bill001g

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I wish I could. They don't let me play with their toys. I just use VLC and stream files or webcams to test multicast. When they are running real feeds I am spending all my time tracking down which of the many routers in the path are preventing users from receiving it. I forget who they bought the software from it is a package deal that is designed for live corporate presentations.
 
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