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Standard User BatBoy
(legend) Fri 19-Apr-13 01:26:49
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Re: Effect of IP profile and how do individual ISP's use it


[re: yarwell] [link to this post]
 
Interesting comment in benstrongs blog
s9 said...

Um, RFC 3390 is an update to RFC 2581, which was obsoleted by RFC 5681. The maximum initial window specified by RFC 5681 is four.
I guess benstrong didn't wiki it either http://en.wikipedia.org/wiki/Slow-start


__________________________________________________________________________The back pedalling starts here__________________
Standard User Chrysalis
(legend) Fri 19-Apr-13 16:28:45
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Re: Effect of IP profile and how do individual ISP's use it


[re: yarwell] [link to this post]
 
I know they cheat but thats just a jump start on the ramp up rather than starting at full speed.

BT Infinity 2 Since Dec 2012
Standard User legume
(experienced) Mon 24-Jun-13 00:18:50
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Re: Effect of IP profile and how do individual ISP's use it


[re: yarwell] [link to this post]
 
In reply to a post by yarwell:
My maxing out occurred on a 2M line wrongly assigned 622M as its throughput doing a bonded link with another 2M line, one was maxed out and the other was useless, as it was getting 2/622 or some similar fraction of the total throughput.


I would think misconfigured load balancing is a different issue from what is being discussed here.

From tcp's point of view I can think of no difference between hitting your bottleneck before or after it's gone from ISP to BT bras.

It will be a bit better for the ISP to create the bottleneck as it should save some small amount of packets being sent over their expensive BT connection that will be dropped anyway.

It will be a lot better for the ISP saving their BT link if you get DOSed - but then as has been said, maybe ISPs that don't follow IP profile still set some limit, or have other DOS workarounds.


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Standard User yarwell
(sensei) Mon 24-Jun-13 10:27:31
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Re: Effect of IP profile and how do individual ISP's use it


[re: legume] [link to this post]
 
I would think misconfigured load balancing is a different issue from what is being discussed here.
It was an illustration - everyone's link is effectively load balanced due to the oversubscription, as we're all running in tunnels and not one big tcp/ip sea.

So the profile system allocates an appropriate amount of bandwidth to each tunnel which makes sense to me as there's no point in giving a 1M customer the same share of the total at peak times as you would give to a 10M customer if the result was the 1M case being maxed out.

The other reason for the profiles is that on 20CN ATM based systems with no buffering the TCP/IP performance under congestion is poor when cells are lost which contain fragments of TCP/IP packets. The steep fall off in performance is well documented. Profiles stop the ATM links being overloaded with data they can't usefully forward.

I assume the people who wrote the RFC for a BRAS had a grip on these things, more than anyone here at least.

--

Phil

MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics
Standard User mixt
(experienced) Mon 24-Jun-13 12:35:38
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Re: Effect of IP profile and how do individual ISP's use it


[re: jelv] [link to this post]
 
FYI, AAISP do copy the IP profile speed, or some factor of it (configurable by the user).

http://aa.net.uk/kb-broadband-shaping.html

They explain in detail why do this (quite a good read, if you have the time). On my line, I have set the AAISP limiter to 99% of my BT profile rate because AAISP apply some basic traffic shaping to give priority to VOIP and other small packets. Limiting to just less than the BT limit means their equipment can intercept and shape inbound traffic before it hits my router, well before any "dumb limiting equipment" at BT limits it instead (which has no traffic shaping/prioritization at all).

Now on <aaisp.net> (21CN+IPv6+FTTC/40Mb)
Previous ISPs: Virgin Media (50Mb/Cable), Be* Un Limited, ZeN
Is Linux routing your internet connection?
Need to make BIND geo-aware?
Standard User legume
(experienced) Mon 24-Jun-13 12:43:58
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Re: Effect of IP profile and how do individual ISP's use it


[re: yarwell] [link to this post]
 
In reply to a post by yarwell:
I would think misconfigured load balancing is a different issue from what is being discussed here.
It was an illustration - everyone's link is effectively load balanced due to the oversubscription, as we're all running in tunnels and not one big tcp/ip sea.

So the profile system allocates an appropriate amount of bandwidth to each tunnel which makes sense to me as there's no point in giving a 1M customer the same share of the total at peak times as you would give to a 10M customer if the result was the 1M case being maxed out.

The other reason for the profiles is that on 20CN ATM based systems with no buffering the TCP/IP performance under congestion is poor when cells are lost which contain fragments of TCP/IP packets. The steep fall off in performance is well documented. Profiles stop the ATM links being overloaded with data they can't usefully forward.

I assume the people who wrote the RFC for a BRAS had a grip on these things, more than anyone here at least.


Yes, I agree with the above reasons for BT wholesale setting profiles.

The point I was trying to make was narrower than that, and specifically about whether or not and what effect the ISP shadowing the profile on their kit has.

I still don't see (apart from differences between the exact mechanism like buffer vs police) that tcp will notice where the bottleneck is.

As bras may limit/balance at peak times any ISP profile setting isn't even going to be hit then, though maybe these times are rarer now than in the past.
Standard User Chrysalis
(legend) Tue 25-Jun-13 07:32:26
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Re: Effect of IP profile and how do individual ISP's use it


[re: legume] [link to this post]
 
the bit I disagree with yarwell on is how tcp deals with profiling.

It simply doesnt, tcp doesnt care if its a dialup modem, a 10mbit ethernet connection or a OC192. It starts at a single packet payload and ramps up from there until it finds a sweet point. Some servers are configured to have a higher ramp up starting point but the principle remains the same.

Generally speaking the only realistic way I can see if a line is getting too much data shoved down it is either a denial of service attack which someone else also mentioned in this thread, excessive syn packets, or something thats broken.

BT Infinity 2 Since Dec 2012
Standard User jelv
(knowledge is power) Tue 25-Jun-13 10:51:00
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Re: Effect of IP profile and how do individual ISP's use it


[re: Chrysalis] [link to this post]
 
So how does that work if you already have a download running that has found the sweet point and then start a second? Or worse try to make a VoIP call.

jelv

Plusnet user since November 2001 - not sure for how much longer
Standard User Kper
(regular) Tue 25-Jun-13 12:10:20
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Re: Effect of IP profile and how do individual ISP's use it


[re: jelv] [link to this post]
 
This is how PlusNet's Head of Products and Digital Care (KellyD on these forums?) explains the way their profiles are applied in conjunction with the BTw IP Profile:
There are 5 potential speed points on your line, applied in this order:

1 - Your theoretical speed. This is the quality of your line. You will never get higher than this without technology changes
2 - Your BT Speed Profile. This is a profile set on your line which the exchange equipment has determined as your stable speed. On a good, stable line this will set and shouldn't change too much. If you have an unstable line, it will theoretically decrease until your line becomes stable.
3 - Your Plusnet speed profile. This is set to a little below your BT speed profile. We do this so that we can control the maximum amount of data we send down your line. This allow us to use our QoS to protect your experience.
5 - Rate limits. We are able to apply a rate limit across our traffic. We do this on our Essential, Plus, Extra and legacy accounts at peak hours for protocols like P2P. Our current Unlimited product does not have any.
6 - QoS level buffering/packet drops. Because we've identified the types of traffic you are using, we can cause packets of those particular types to buffer, and eventually drop. We use this to ensure that, along with your Plusnet speed profile, if you are maxing your bandwidth, we'll make sure you get your high priority packets first. If our network is also under heavy load (i.e. we've cocked up our bandwidth forecasting) this will start to apply to ensure time sensitive traffic is protected at the expense of the less time sensitive traffic.

Unlimited has no 5, and 6 is applied on a per user level if you are maxing your line. 6 is always in affect, but our WBMC network is scaled so that no buffering is happening. (There has been a little bit on IPSC over the past few weeks which I'm working with Dave T to fix)

We can set 3 at any time by hand, but is usually automatically adjusted a couple of times a day based on messages from BT about what 2 is set as. (THere are some issues in the messages coming from BT on this.) This manual adjustment is what I did for Finguz

We can't influence 1 at all, beyond advising you to fix dodgy cables and sending engineers.
Standard User legume
(experienced) Tue 25-Jun-13 12:39:31
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Re: Effect of IP profile and how do individual ISP's use it


[re: jelv] [link to this post]
 
In reply to a post by jelv:
So how does that work if you already have a download running that has found the sweet point and then start a second? Or worse try to make a VoIP call.


If another TCP starts then the first will get more loss and back off. TCP isn't fair so what rates they get will depend somewhat on the latency between the endpoints.

Historically at least BT BRAS buffer quite a lot which can be seen as a bad thing - buffer bloat, and is not nice for voip.

As has been said, some ISPs will help here doing Qos for you by setting their rate a bit below BT profile.

IME an ISP that has a policer set at ipprofile rate still fills the bras buffer as they have to set a burst as policers tend to be a bit aggressive otherwise. Policers just drop - no buffer, but in practice they use a virtual buffer = burst.

ISPs using ip profile to do active QOS for you is a good thing - if yours doesn't you can do it your self but being the wrong and of the bottleneck makes it harder and involves sacrificing bandwidth. The slower your line the harder it is.

Of course no ISP using BT wholesale can guarentee QOS like this as at peak times the bras buffers may run below line speed - though this may be rare.

BT wholesale will sell QOS to ISPs to avoid this but it's expensive, I think BT vision uses it - but then I guess expensive doesn't matter so much if you can keep it in the family smile
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