topic Re: Actual wireless link speed low in Wireless

Actual wireless link speed low

urvininocente — Sun, 04 Jul 2021 06:00:47 GMT

Hi,

I have 2 cisco Aironet 1252 setup as a point to point link using an external antenna (one radio is setup as the root bridge the other is setup as the non-root bridge). Now I see that the connection between the radios is established at a speed of 54 Mbps. However when I perform a speedtest on the link I see that the my actual download speed does not exceed the 2,5 Mbps.

Any idea what can cause my actual speed to be far lower than the 54 Mbps? And what can I do to improve it?

Regards,

Screech

Actual wireless link speed low

George Stefanick — Fri, 09 Nov 2012 19:50:26 GMT

Hi,

Wireless is a half duplex medium. When it says you are connected at 54 you will not actually do 54. At best, with low contention you can hope for 1/2 that. But if you are only getting 2 or 5, there could be contention.

What is the distance between the bridges. Also are you testing this on the wired side of each bridge ?

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Actual wireless link speed low

urvininocente — Fri, 09 Nov 2012 23:25:17 GMT

hi,

I estimate that the distance to be around 3 to 4 km. Furthermore i am testing it on the wired site of the bridge.

Screech

Re: Actual wireless link speed low

Scott Fella — Sat, 10 Nov 2012 04:16:09 GMT

That is pretty far for a 1252 setup as a bridge. I'm not surprised your getting those speeds

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Re: Actual wireless link speed low

George Stefanick — Sat, 10 Nov 2012 05:18:59 GMT

I would agree..

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Re: Actual wireless link speed low

Scott Fella — Sat, 10 Nov 2012 18:25:27 GMT

The main difference between an indoor ap vein used as a bridge and an outdoor bridge is the max TX power. Your limited to 100mW and the 1300 or 1400 and other vendors can max at 200mW. Using an indoor ap as a bridge is fine when you connecting two buildings that are close in my opinion. Going 3k 4k, you need a real bridge.

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Re: Actual wireless link speed low

urvininocente — Sun, 11 Nov 2012 17:25:11 GMT

I have 1252 connected to an external antenna with a 23 or 27 db gain ( don't remember the exact vale), does this make any difference? Furthermore is there a specific reason why the associated brisge connection shows that the actual link connecion speed is 54 Mbps while the actual throughput is far less.

Regards,

Screech

Re: Actual wireless link speed low

Scott Fella — Sun, 11 Nov 2012 17:35:38 GMT

Here is the thing... What your seeing is what the bridge is using for modulation not what the throughput will be. Have you done the freznal zone calculation, because having a link that far requires you to make sure your antennas are high enough.

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Re: Actual wireless link speed low

urvininocente — Sun, 11 Nov 2012 19:15:23 GMT

Do you now of any utility\software that can help me determine or even better measure the actual throughput of the link.

Regards

Screech

Re: Actual wireless link speed low

Scott Fella — Sun, 11 Nov 2012 19:33:49 GMT

I typically either use jperf/iperf or an FTP client that measures upload/download throughput. Bandwidth Meter Pro I also use to test from my machine.

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Re: Actual wireless link speed low

urvininocente — Tue, 13 Nov 2012 02:34:00 GMT

Ok found. The source of the problem. The problem was being caused by a duplex mis-match on one of the interfaces of a router in our network. Now we are seeing throughput around 20 Mbps on the wireless link (20x faster) which should have a theoratical maximum speed of 54 Mbps. Is this an acceptable value for the wireless bridge that covers a maximum distance of 1.8 km?

Regards,

Screec

Re: Actual wireless link speed low

Scott Fella — Tue, 13 Nov 2012 02:48:10 GMT

That speed is fine. Since the link is half duplex that is around the expected throughput. Max is usually half of the connection speed minus obstruction or rf noise.

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Re: Actual wireless link speed low

Scott Fella — Tue, 13 Nov 2012 03:35:40 GMT

I thought that you were testing directly from the ethernet of the bridge from one of your post.... That is why I figured it must be an rf issue not a network issue:)

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Re: Actual wireless link speed low

urvininocente — Tue, 13 Nov 2012 03:56:35 GMT

That was a troubleshooting mistake from my site.

Since the link is half duplex so you expect half of the 54 Mbps as the throughput what do you recommend to configure as the bandwindth on the router interface ( this is used for Qos and routing purposes) 54 Mbps or 27 Mbps.

Regards,

Screech

Re: Actual wireless link speed low

Scott Fella — Tue, 13 Nov 2012 04:01:13 GMT

You configure the router interface as you would normally.... the wireless link is half duplex and that is why its half the connection. The ethernet port of the bridges would still be configured as auto. Seeing 27mbps or less would be normal.

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Re: Actual wireless link speed low

urvininocente — Tue, 13 Nov 2012 04:09:14 GMT

OK so that means then that as soon as I see the utilization reaching 27 Mbps you can conclude that the link is getting congested.

I am asking because our network monitoring tool uses the configured bandwith on the router interface as the capacity of the link that is connected on the router and it is herefore that I was thinking if I should configure 27 or 54 Mbps (although the interfaces are ocnfigured as auto)

Re: Actual wireless link speed low

Scott Fella — Tue, 13 Nov 2012 04:12:59 GMT

Its hard to say.... but that would be a good start... If you test throughput and your getting 22mbps, I would use that as a baseline. Try to have multiple devices upload or download across the link and then check the speed. Its easier when your doing a ftp transfer if the ftp client or server can show you the upload or download speed.

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