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Actual wireless link speed low

urvininocente
Level 1
Level 1

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

16 Replies 16

George Stefanick
VIP Alumni
VIP Alumni

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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"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
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‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
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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

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

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-Scott
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I would agree..

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"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________

Scott Fella
Hall of Fame
Hall of Fame

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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-Scott
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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

Scott Fella
Hall of Fame
Hall of Fame

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

Regards

Screech

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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-Scott
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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

Scott Fella
Hall of Fame
Hall of Fame

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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-Scott
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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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-Scott
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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

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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-Scott
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