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Author Topic: Birmingham RAS  (Read 1687 times)

Smoke

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Birmingham RAS
« on: December 16, 2009, 09:09:53 PM »

Hi All,

Odd one this, but here goes. Over the last few days (from the 4th approx. onwards) I have noticed a big reduction in my download speed (5.5mbps - 2mbps) and during peak times a big increase in my latency. (25ms - 100ms+)

As its been years and years since I had a problem like this I decided to do some investigation. I checked my sync rate 6304kbps seems ok - checked my IP profile 5000mbps no problem there.

At this point I contacted my ISP Eclipse who were very helpful and did some checks they could see no line errors and the IP profile was as was reported and they confirmed that it wasn't congestion on their network by logging in on one of their test adsl lines with my user details.

This placed the problem either at the exchange or on the BT network. The guy on the phone was fairly certain it was exchange congestion but Im not so sure as its a small exchange here (very rural) and I am certain theres hardly any IPStream Max connections to it like mine as there are next to no businesses connected to this exchange.

However I recently found this on AAISPs status updates.

http://aaisp.blogspot.com/2009/12/open-birmingham-and-kingston-20cn.html

BT obviously make no mention to this. But I am guessing this is probably the cause. I spoke to a friend of mine who is on a completely different exchange which uses the Birmingham RAS and has reported similar problems to mine.

I was hoping if anyone could confirm if this problem is the likely cause and if anyone has ever heard of congestion at a RAS before? I was also wondering if any users here on the Birmingham RAS could report any similar issues over the last 1-2 weeks.

Thanks in advance.

Mark

EDITED: to add that I am on ESR7.Birmingham5
« Last Edit: December 16, 2009, 09:14:07 PM by Smoke »
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kitz

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Re: Birmingham RAS
« Reply #1 on: December 17, 2009, 11:10:21 PM »

>> Im not so sure as its a small exchange here (very rural) and I am certain theres hardly any IPStream Max connections to it like mine

Just as an aside - The VP backhauls are scaled accordingly and its a myth that if you are on a rural exchange you have less chance of exchange congestion.  In fact the smaller the VPs and the less people on them actually because of the way contention works, means that less people sharing the relative same amount of bandwidth, then the more likely it is for you to see contention.
eg if 2 people were sharing a 8Mb link at 2:1 then theres a good chance you will see some contention.   The more people sharing the more varience of their habits therefore less likely to see the effects of contention.

>> if anyone has ever heard of congestion at a RAS before

Not specificially, but I have definitely seen cases of rerouting to different RASes causes increase/decrease in latency. 
Since the RAS will also have a link to either the Colossus network or 21CN network depending on which network youre on... Then yes its entirely possible that if BT didnt keep an eye on things and order new fibre in time for the link...  then its entirely possible that it could occur.
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Smoke

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Re: Birmingham RAS
« Reply #2 on: December 17, 2009, 11:32:44 PM »

Hi Kitz,

Thanks for that. One of the reasons I didn't think VP congestion was an issue was down to the checkers always reporting the VP status as green. But I'd like to know just how accurately this is reported. Also my friend on a different exchange but routing via the Birmingham RAS was reporting similar issues.

Things seem to have improved slightly. My latency is back down to something sensible (25ms) and my throughput is back up. I also noticed this status update on aaisp.

http://aaisp.blogspot.com/2009/12/open-birminghamkingston-20cn-ras.html

Cheers
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kitz

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Re: Birmingham RAS
« Reply #3 on: December 18, 2009, 02:06:34 AM »

"Usually" if it is exchange congestion you wouldnt see an increase in latency.  The dslams installed since 2003  can perform low level QoS.   Ive seen cases of very bad exchange congestion, but none of them have seen any probs with latency.

From what has been reported so far from AAISP and your experience it doesnt look like the RAS boxes do QoS...  perhaps expecting it all to be handled by the dslams & msans.  There are lots of RAS boxes at a RAS location, so I should imagine that its the actual link from the RAS to Colossus that is suffering from bandwidth.   Weird that it should happen when they are moving over so many to 21CN.  Wonder if theyve reassigned some of the fibre and not left enough for 20CN?

As regards to red exchanges...  I dont think any exact figures have been released, but it used to be once speeds got down to around the 400kbps mark.   Get a good period again and the checkers will swing back into green on their own and I believe there is a period of time before an upgrade is actually processed and upgraded.
 
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Smoke

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Re: Birmingham RAS
« Reply #4 on: December 18, 2009, 07:36:12 PM »

Hi Kitz,

Thanks again for the info. It always amazes me just how low a speed has to get off normal before BT consider taking any action on it. It will also be interesting to see how BTs backhaul holds up as more people move over 21CN.

It looks like BT completed their emergency work last night and I am pleased to say my throughput is back up from 2mbps to 5.5mbps with a normal latency of 25ms.

Cheers
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