1300 Bridge Speed Issue

chrisareston · ‎09-01-2007

I have two buildings that are only about 200 feet from each other. I have two 1300 bridges joining both buildings. This works great! The only thing that I notice is when I copy files from our file server in one building to my PC in the other building it takes 7 min for a 700M file, and I use a monitor and see that the wireless is only transfereing 2.4MPS off of the wireless interface. I have both bridges set to require 48MPS and 54MPS and all other is disabled. Why am I not getting the full 54MPS copying the file? The rest of my network is on gig switches.

Thanks

Rob Huffman · ‎09-01-2007

Hi Christopher,

Don't forget that the 54M numbers are really only theoretical and not a reflection of the true throughput,with the subtraction due to overhead the actual throughput is much lower. Have a look;

Approximate Throughput Comparison for 802.11a, 802.11b, and 802.11g

802.11b Data Rate (Mbps)=11 Approximate Throughput (Mbps)=6

802.11g (no 802.11b clients in cell) Data Rate (Mbps)=54 Approximate Throughput (Mbps)=22

802.11a Data Rate (Mbps)=54 Approximate Throughput (Mbps)=25

From this good doc;

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_white_paper09186a00801d61a3.shtml

Here is a nice explanation from one of my favourite NetPros Scott;

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Wireless%20-%20Mobility&topic=WLAN%20Radio%20Standards&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddcbbd2/3#selected_message

Hope this helps! I know its a bummer :(

Rob

chrisareston · ‎09-04-2007

Rob

Thank you for the links! I am only getting about 2.4Mbps and there are no wireless clients connected. I have a wireless bridge on each building and they both go into gig switches. Saturday I was the only one using the bridge since everyone else was gone and I tested copying a large file and I was only getting the 2.4Mps, when I copy the file from the same building not using the bridge my time goes from 7 min to 1 min! I have the bridge set up to only use 54Mps do you have any other ideas on settings? Thanks

chrisareston · ‎09-04-2007

Anyone?

andrew.brazier · ‎09-05-2007

Tried a carrier busy test (best to run on both bridges)? Might show up some interference. Also, check the transmit/receive stats for excessive retries, dropped packets, etc.

Also, although I think from your tests you can discount it, have you got speed/duplex mismatches on your switch ports? That can murder throughput, make sure you nail the switch ports and the bridges ethernets to 100/full

chrisareston · ‎09-05-2007

Andrew

Can you look at this and tell me if it looks ok. I cant do busy test right now because it will take down the wireless. Im not sure why 1Mbps is showing anything I have both bridges set to only allow 48 and 54 all other speeds are disabled.

Thanks

andrew.brazier · ‎09-05-2007

Well, I'll admit I'm not the worlds No 1 expert on these things but those stats don't look too bad to me. There's a bit of 1MB traffic but almost all your traffic is recorded as being at 54MB. There aren't too many errors of any one kind which (I think) indicates your wireless signal is fairly clean. Carry out the CBT test when you get the chance as it may show up something. I presume you have the bridges nailed to a channel? Also, are the switchports and bridge ethernets nailed as per my last post? I've seen bridge links blamed for this sort of problem in the past when it was a misconfigured switchport all along.

PS: Next time, could you post the screenshot as a jpeg, that BMP was over 3MB! : )

chrisareston · ‎09-05-2007

Andrew

Thank you! Yea next time I will post it as a jpg sorry. As far as the channle I have the bridge choose the least used, should I have both bridges set to only 1 chan?

Thanks

Chris

andrew.brazier · ‎09-05-2007

Chris,

No problem! As for the channel, do the CBT test (repeat it several times as each run is only a snapshot) and nail the root bridge (the nonroot won't allow you to nail channels) to a channel which looks quietest. Normally in a WLAN deployent you'd stick to channels 1, 6 or 11 but in a bridge deployment unless you have other APs nearby that might give you overlap problems there's no need to (well, I don't bother too much!)