image processing over wireless

[suthomas1]

Hi,

One of our subsidaries has a setup where continuous video stream is generated from certain application servers processing real time image processing.

The setup goes this way; 3 PC's which run these image processing & are connected to a 3750G switch.

This switch is uplinked to an access point which then carries all these over wireless to the image processing main server.

About two weeks ago, when they tested this ,all 3 PC's had issues running together when operators viewed/worked upon the images on them.

When either one or two of them is turned off, the rest works fine with no disturbance( intermediate stop & start of images ).

Please help with suggestions on what could be the cause. I suspect bandwidth, but since this doesn't cover any WAN links, i doubt that bandwidth is actually the problem.

Thanks in advance.

[Richard Atkin]

So you have three PCs plugged in to a switch, then the switch connects to the network via a Wireless Access Point?

Presumably the AP is configured as a Workgroup Bridge? and both APs are Cisco?

How much traffic do the video streamers generate? And what type of traffic is it?

Is there anything else using the Wireless?

What data rate do the APs associate with each other at? And at what Frequency?

Is the connection between the 3750 and the rest of the network configured as a L2 or a L3 connection?

[suthomas1]

Yes, the switch connects to network via the cisco access point and AP is configured as bridge.

the imagers generate about 1.5 Mbps of traffic and its sort of video image.

The wireless is also used to a small extent by few users. But the primary purpose is to transmit the images back to the server.

The switch is a layer 2 switch connecting to the access point.  they communicate on 802.11a channel to transmit the feed back to the main server.

thanks

[Scott Fella]

When you say bridge, you mean you have a point to point bridge? What exactly is the model of the bridge and can you share the configuration.

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[suthomas1]

AP model is 1142 which is used in mesh mode.Few of these AP's carry the image back to the core network.

Configuration wise, it has a static ip address, bridge gp name.

The AP port connected to the switch is in trunk mode.

thanks & let me know if any other information is needed.

[Scott Fella]

I run a indoor mesh using 3602's and sometimes the downloads are slower than uploads. So your using Ethernet bridging I'm guessing and the map and the rap have Ethernet bridging enabled. Your placing the traffic from the users in the trunk port the RAP is connected to correct? To be honest, I don't get the performance I expect when connected to the MAP. I get higher throughput when connected to the RAP. How's the connection between the MAP and the RAP?

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[suthomas1]

Thanks Scott.

Yes, ethernet bridging is enabled. MAP to RAP looks pretty good with SNR being 32.

when one of them the viewing stations ( which view these image streamers ), the image quality gets better for viewing on the other station.

But with both on at the same time, there is a bit of tardy shakiness to the images.

Would qos help here, just wondering this is normal lan.

[Scott Fella · Accepted solution]

It depends. QoS will help if your having congestion on the wired side. WMM QoS will help for over the air. I would look at the switch port and see if you see drops on both the map and rap side. You might just be over utilizing the backhaul. Remember that it is half duplex link so that can be an issue also. I had an install with regular AP's and 3gb video uploads within 30 minutes and the only way to achieve that is only allowing 4-5 clients per AP. the testing you have done seems to show that the max you can do over that link is 2. How much other traffic is using the wireless. Maybe try to isolate those traffic on a separate RAP/MAP pair using AP Groups.

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[suthomas1]

The remaining user traffic is very minimal with about 3-4 users at times using outlook email or so. Nothing much that users use it for.

Any ways to find out if the backhaul is going above the rate? & can you please help me on WMM Qos configuration so i can see to it.

Thanks again!

[George Stefanick]

What are your rates set at on the 5ghz side ?

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[Scott Fella]

Download jperf and load that in two laptops. Place one on the switch that connects to the MAP and the other on the switch the RAP is connected to and see what throughput you get. Then I would connect them directly to the Ethernet port of the MAP to see the difference. Then you can also perform back to back testing to see how much between the device. Now you possible can load jperf on the two devices that are doing the image processing to get a baseline.

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[George Stefanick]

I would also add. It might be worth it to do an iperf across the link to see what bandwidth you are able to send across the link. Perhaps conduct 3 iperfs at the same time with 6 individual pcs.

Also check the traps, make sure you don't see anything odd.



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[Scott Fella]

I believe the mesh bridge rate is set to auto.

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[suthomas1]

Yes the rate is Auto.

I'll try with Iperf, i have never used it before!

Any thing in specific i should take note of when using iperf, best way to use or so?

Thanks for the inputs!

[Scott Fella]

I just ran iperf (wireless to wireless) from my iphone and my ipad and I get half the throughput when testing from both devices connected to the RAP (avg 10.07 Mbps) than fro the MAP to the RAP (avg 6.20 Mbps, lowest 2.21 Mbps) just to give you an example.  This is with not much traffic on the wireless also.

Thanks,

Scott

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