|
Small packets ok... sustained lost. |
|
|
|
|
Written by kukur
|
|
Thursday, 18 January 2007 |
" Forgive the lenghty intro, but I want to make sure I don't leave any info out that may prove important.
Just before Christmas we had a pretty bad wind storm. I thought we had faired well but started noticing some problems with our backhaul. After trying to realign the backhaul several times, we still couldn't return the service to prior levels. I figured the antenna or cables were damaged some where I couldn't find and just abandoned that set and put in a new set of bridges... problem solved. Will go back up the tower when it is warmer and worry about the old set.
Now, about that same time one older client (2.5 years) lost connectivity. At her location I can ping out to the internet (sustained ping shows no dropped packets), I show noise levels at around 97db and signal strength at 77db. But when I try to pass more traffic than just a ping, it drops. It seems as though the CPE is sending the request, but the info isn't returning. I have replaced everything at her location and the same problem occurs on both her computer and my laptop.
As I have been trouble shooting this client another client just down the road (almost in the same line of sight as previous client) called for an install.
Same problem, good signal - low noise, can ping till the cows come home but can't move traffic.
If I attempt to log into my AP from the client's location, I get the login almost immediately, but once I submit that info... no traffic. It seems I can send small bursts of info but no more.
I have tried changing the channel on the AP with no luck. The other 30 customers on the same AP are happy.
The bizarre thing is I can access the CPE from the office without problems.
I am starting to wonder if the AP's antenna has moved enough to create a geographical problem in that area. Perhaps this area is on the very fringe of the sector antenna's signal and although showing a good signal, isn't able to remain stable.
Any insight would be helpful."
lutful:
1. 30 CPEs are working fine on a particular AP.
2. But from 2 CPE locations, using either your laptop or customer desktop:
- you cannot browse sites on the web
- you cannot browse the AP management page
BUT you can ping sites on the web
3. From your office, you can access these 2 CPEs through the network.
My initial thought is that AP-CPE signals are OK but maybe something has changed in the configuration of these 2 CPEs.
Can you properly reset them to factory default and very carefully reprogram them to be just like one of the working CPEs?
Also check if your AP shows the RSSI per CPE. That info will be helpful if above suggestion does not work.
kukur:
1. Correct
2. Correct
3. Correct
I have installed a new CPE at the old client's location with same results. Defaulted, re-configured the CPE and used 3 different firmware versions thinking the same thing. No difference.
I brought the original CPE back to the office and it connected fine here to a different AP.
Here is a shot of the APs info for the customers...
»smgazette.com/old-customer.jpg
»smgazette.com/new-customer.jpg
Here is the performance stats from CPEs
»smgazette.com/old-cpe.jpg
»smgazette.com/new-cpe.jpg
Here is a ping sequence to both...
»smgazette.com/old-ping.jpg
»smgazette.com/new-ping.jpg
My next step is to take the original CPE back out and do a site survey with it and see if it will communicate in a different location to the same AP.
gunther_01:
I would venture to say that your AP or AP's antenna and or cable is having a problem. I would bet that your other clients have dropped somewhat as well but maybe they are closer so it doesn't effect them as much. (graphing has helped me here)
The client has good signal but your AP shows a poor signal quality and low data rate. You will easily see through ping, that higher packet sizes will start to fail and time out. I would look out for new interference from maybe that wind storm you mentioned (pole transformers maybe).
lutful:
Cisco AP is getting almost 50% packet re-send requests from these CPEs when sending to CPE at 2Mb/s rate.
Cisco AP is receiving thousands of packets from the CPEs without error at 1Mb/s rate and 50% signal strength.
What model CPE are these? You mention they are 2.5 yrs old? I very much doubt the -95dB noise reading since CPE is not managing to receive at even 2Mb/s.
kukur:
It was an older Tranzeo CPE2 - but both are now fresh Tranzeo CPQ units.
The bandwidth is low because I thought there might be not enough stability to hold 11mbs - so I set the CPE at 1mb for testing to see if that would help.
Everything points to something at the AP antenna not broadcasting as cleanly as it should from what I see. I was hoping to get through winter and then had the plan set to replace/add new APs. Looks like I may not have that luxury.
I have checked other clients more in the sweet spot of the APs range and am finding retry requests there as well (not nearly as bad however) just as gunther alluded to.
goldenspacek:
I bet the AP can't hear the CPEs. Look at the signal levels there and check noise at the AP. Your 77db client could be -85db at the AP.
Same thing happened to our Cisco WGB350 APs. I found there was a bad antenna cable that made it hard for the AP to hear the other radios over the surrounding noise. So those that were yelling the loudest worked fine.
Also for testing use this command
ping xxx.xxx.xxx.xxx -l 1024 -n 30000
That will send a 1024 byte packet 30000 times. Pings are only 32 bytes, so it is easy to retransmit small packets.
lutful:
But please remember that exact same antenna and cable is receiving without any error. It is even receiving all those retry requests from Tranzeo without error.
Anyway can you fix the Cisco AP to transmit at 1Mbps too? One issue could be how Tranzeo firmware handles continuous switching between 2Mbps to 1Mbps speeds.
gunther_01:
While others have had good luck I suppose. I have never had a good, stable or otherwise working connection when I fix or have a radio using 1mb data rate. If it can't at least sustain 5mb I fix it or it's a no go for an install simply for that reason. Others experience varies it seems.
I will ask if the other clients on this AP also read 50% signal quality on the AP. Signal Quality is different on just about everything, but, I still have a problem with that reading 50% (biased opinion from Star V3 signal quality reading). I will stand by my Interference or AP side radio, cable, antenna problem. Especially since it has just happened after 2 plus years, and replacement CPE's had the same result.
LLigetfa:
There was anecdotal evidence posted recently where the weaker Rx signal passed through bad coax fine but the stronger Tx was getting discombobulated. It is a theoretical possibility.
lutful:
I recall such a conjecture put forward by John Galt in response djhurt during the summer months. Unfortunately the cable was discarded before any tests could be done.
Since then I have collected, tested and posted photos of some visibly damaged cables that amazingly still work.
I can say confidently that if the RF signal path is damaged in such a way that 1W signal is "shorted to ground" at certain points during common modulation schemes, the same scenario will occur so many times during a single packet transmission that no packet could be transmitted without error.
But this Cisco transmitted and recieved thousands of packet successfully, so there is something else going on.
Keithb:
I believe it was Stealthwave who was having the issue with the coax this past summer. I recall a thread and talking to him about that.
Original thread location |
All Categories 
