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Author Topic: Great - not!  (Read 9642 times)

guest

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Re: Great - not!
« Reply #30 on: November 21, 2007, 03:21:59 PM »

Well I'm not sure that its a case of "not using it". I think perhaps something is just a bit broken in the new DSLAM firmware because it still sort of works. I suspect that the "upgrade" may have had more to do with enforcing the 16Mbps "limit" that the service has now.

I still get more than 16Mbps obviously but perhaps I should start monitoring latency a bit more just in case 22Mbps legacy customers = bad boys and get contended as such. 16Mbps customers are 20:1 max and 22Mbps are 33:1 remember? :P

I think SRA may be a bit problematic in that it tends to run right up to the limit so CRC errors are always present. Not many but I can't help wondering what the real effect is on upstream links. I'm thinking in terms of links across the Atlantic which are usually run at close to 90% capacity at all times*. You get big enough RWINs (from "tuning" sites) and the retransmissions would become significant I reckon. One thing is for sure kitz, none of the current ADSL2+ operators are showing much enthusiasm for SRA. There has to be a significant financial reason for that I think as the savings in support costs are obvious but........  :shrug2:


*By "links" I mean rented transit rather than "We own the fibre". Either way its still expensive - ask Be (Telefonica) who threw at least one 10Gbps transatlantic link at a problem to see the bandwidth saturate on new links within weeks.
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kitz

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Re: Great - not!
« Reply #31 on: November 21, 2007, 11:19:17 PM »

>>> I think perhaps something is just a bit broken in the new DSLAM firmware because it still sort of works. I suspect that the "upgrade" may have had more to do with enforcing the 16Mbps "limit" that the service has now.

:(

>> There has to be a significant financial reason for that I think as the savings in support costs are obvious but........ 

I cant quite figure that out ...  aside from continually running at max could obviously cause some problems - but surely there are still other configurable aspects such as target SNR?

"In theory 33:1" should be ok - but obviously it depends on the type of user at your particular exchange.  Unfortunately those who elected for the higher speeds are probably most likely to be higher users :(

>> I should start monitoring latency a bit more

You know your BTw exchange is one of the very few which Ive seen suffer from latency problems due to contention (ignoring all the long grass stuff).
In all the times that Ive suffered contention despite from some very low speeds Ive never had a problem with latency nor did the other 30+ users on our exchange.  Ditto with the 1Mb and 2Mb upgrades.  Poor speeds but latency ok.  About 12-18 months ago when about 60% plus exchanges were on red I was monitoring AG and although poor speeds were an obvious issue I never saw anyone complaining about latency.

I suspect that some dslams are capable of doing a basic type of QoS and BT do use it for stuff like latency.  IIRC you were on one of the early enabled exchanges with possibly an older type dslam.  The Juniper ERX's installed by BTw during the period circa 2003-2005 certainly is capable of doing a basic form of traffic prioritisation.  Its were the gold/silver/bronze stuff came from in the first place.
I was told in 2004 that its the older CISCO dslams that have problems identifying traffic/account types and hence why BT replaced a load of CISCO dslams in 2004 with Junipers.

>> *By "links" I mean rented transit rather than "We own the fibre"

Still cheaper than centrals though :D
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guest

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Re: Great - not!
« Reply #32 on: November 22, 2007, 08:21:38 AM »

Yeah the DSLAM I used to be on was a first-gen Alcatel so QoS was probably a "feature" - ie didn't work properly :D

The SNR doesn't appear to be configurable with SRA active - not from the user side of things anyway. Mine stayed at 6.2dB regardless of what I set the target margin to using DMT.

Re latency - I've always been able to see latency increase relative to traffic load. I don't mean my traffic either. I could see the gateway latency vary on Be depending on time of day and I can see the same thing on UKO. We are talking about 5-20ms increase here so the average punter wouldn't notice as its obviously more of a "spikey" increase rather than sustained.

Re 33:1 - depends where the contention is applied really - if its at the DSLAM then it's unlikely to get any worse than it is now as its a legacy service. It may even improve due to churn - depends how closely UKO monitor the backhaul transit.
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kitz

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Re: Great - not!
« Reply #33 on: November 22, 2007, 01:34:35 PM »

>> I could see the gateway latency vary on Be depending on time of day

Now you mention it - its something Ive seen on Chris's Be connection too...  although I'll let him comment on that because I wasnt looking in depth.

>> if its at the DSLAM then it's unlikely to get any worse than it is now as its a legacy service.

Thats true
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guest

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Re: Great - not!
« Reply #34 on: November 22, 2007, 01:47:55 PM »

Heh ask Chris about the next couple of hops - I bet he's not stunningly impressed with what he sees ;) When you get no response on the hop after the gateway then its because the router is struggling - to say the least.

You have to wonder about networks which routinely expose non-routable addresses in tracerts - it indicates a serious lack of understanding.
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guest

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Re: Great - not!
« Reply #35 on: December 03, 2007, 11:47:16 AM »

There's been a second "software update" on the DSLAM and SRA now works again.

Can we say "rollback"? I think so :D
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