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DirectWireless
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One-way video broadcast to 5ghz clients

Fri Dec 24, 2004 7:26 am

Okay, imagine I am broadcasting a 36Mbps UDP stream (54Mbps air rate), multicast PtMP. The client units are each recieving the whole stream and picking up whatever channel they're looking for via multicast address. What would happen if one of those clients were to have a bad signal, would it slow down all of the other clients?

I suppose I could force 48/54 Mbps data rate on the tower side, then they simply would lose signal, right? Basically this would be one-way real time video broadcast, so if they lose signal there's no catchup, just lost packets.. (and a waiting for signal screen)

Now to the client side... if I use Routerboards for my clients, and assuming each channel takes up 2 Mbps, even though I'm broadcasting faster than the board can process whole packets, could it pick up just the multicast packets that are destined for it without losing them? I know a routerboard can't process more than 24 Mbps, but would it be able to just ignore the extra packets that it is not waiting for?

I'm hoping that the multicast UDP packets will not incur an ACK response from EACH client on every frame, and rather have the client silently repeat packets to the ethernet side... Kinda like my Dish Network system doesn't tell the satellite it got the TV signal. That would eat up my air time badly.

This is all using 5ghz, probably N-Streme. And I'm sure I'm the first person to try this :)
 
ice
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Mon Dec 27, 2004 10:10 am

looks good, but does MT know how to handle multicasting packets?
 
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sten
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Re: One-way video broadcast to 5ghz clients

Mon Dec 27, 2004 12:24 pm

I'm hoping that the multicast UDP packets will not incur an ACK response from EACH client on every frame, and rather have the client silently repeat packets to the ethernet side... Kinda like my Dish Network system doesn't tell the satellite it got the TV signal. That would eat up my air time badly.

This is all using 5ghz, probably N-Streme. And I'm sure I'm the first person to try this :)
I believe multicast frames use the basic air speed (default 6 mbits) so you would have to up this to 54 mbits. reliable 54 mbit's is really hard to get. Most outdoor installations running at 54 mbits have considerable amount of retransmissions (something which is hard to detect with RouterOS, NOTE TO THE PEOPLE AT MIKROTIK: GIVE US MORE ERROR VALUES! :) However i dont think multicast/broadcast packets need ACK, hence the second air speed setting.

I wouldnt be so sure you are the first person to try this ;-)

- Sten
 
DirectWireless
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Mon Dec 27, 2004 5:23 pm

Well, I was looking over some web sites and I'm not the first person to do video over 802.11a. But what I'm trying to ultimately do is backhaul from one main site up to 100 TV channels to multiple sites using multiple PtMP links. I was thinking 15 channels each, 30 mbps max. I've done 30Mbps UDP data throughput before PtMP.

I streamed a 6-7 Mbps DVD over a 802.11a link in multicast and found the problem you described, which made it not work right. So I will try upping the basic rate.
 
mp3turbo2
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Wed Dec 29, 2004 8:14 am

hi direct,

what software you use for multicasting? We face similar problem : we would like to distribute some huge software packages to several clients at once in order to prevent bandwidth waste (instead of having 10x ftp sessions or so with 15GB each we would like to have 1 broadcast/multicast/whatever with 15GB).

thnx, mp3turbo.
 
DirectWireless
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Wed Dec 29, 2004 3:14 pm

Problem with multicasting software to clients is error correction. Multicasting is UDP, in addition to the fact that the wireless itself doesn't do error correction when multicasting. You could only multicast something like music or video. You could use *broadcasting* (you know, x.x.x.255) which still produces wireless ACKs (and thereby some error correction) but I don't know of any UDP file transfer programs.
 
mp3turbo2
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Thu Dec 30, 2004 7:41 am

hi directwireless,

yeah I know, that's why I was asking for software solution for this. Solution means that there will be some box (either dedicated or this software could run on another linux/windows box with other current services) and it will 100% maintain that delivery, meaning I will not have to care about the broadcast alone, error correction etc.

Something like:
"Hey you, I want to have these 15GBs on those 10 clients, start at 11:30PM and if not finished, stop at 6:30AM".

bye, mp3turbo.
 
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mag
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Thu Dec 30, 2004 11:13 am

i am not sure if i understood your demands correctly, but there's a (partly) open source solution:
http://developer.apple.com/darwin/projects/streaming/
this system is devided into a coding/working server and a broadcasting server.
hi directwireless,
yeah I know, that's why I was asking for software solution for this. Solution means that there will be some box (either dedicated or this software could run on another linux/windows box with other current services) and it will 100% maintain that delivery, meaning I will not have to care about the broadcast alone, error correction etc.

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