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[setecio]

I just want to check I am correct in this assumption :

I've read about how ISPs set a BRAS profile to avoid wasting data down the line that your line can't handle, and that it may take 3 days for this to updated if your sync speeds go up.

Is the sync speed found in a modem admin page limited by anything like the BRAS. Obviously it will be affected by the line itself, but is it limited by any block/limit put on the line by your ISP ?

i.e. If my modem is syncing at 1152kbps and I am on adsl max (up to 8 ), is the regular modem speed sync an accurate display of the speed I should be getting once the BRAS is updated, or can ISPs somehow stop the modem syncing at it's max ? So if my modem is always syncing at 1152 while I am on adsl max, can I take it that that will be my true max, until I can somehow improve the line quality ?

So equally if my modem is syncing at 6816 for 3 weeks, and I am only getting a speed of 0.5Mbps, then I can ring up my ISP and tell them that they are blocking me getting what I should be getting (probably by  the BRAS profile) ?

Thanks.

[mr_chris]

Welcome to the forum

Kitz has a list of how sync speed relates to IP/BRAS profiles on this page. Plus it has loads of info about how the BRAS profile system works, as far as we know (it's still a bit of a mystery from BT, but it's about as accurate as I think anyone knows really!)

So equally if my modem is syncing at 6816 for 3 weeks, and I am only getting a speed of 0.5Mbps, then I can ring up my ISP and tell them that they are blocking me getting what I should be getting (probably by  the BRAS profile)

Yes, 3 weeks is way too long and indicates a stuck profile, either at your end or your ISP's end (they also may do rate-limiting in line with BT, to keep their own network in sync with your true speed too)

[roseway]

Just to be clear about this, it's not the ISP who sets the IP profile, but BT - it's an automatic process carried out by the exchange equipment. But if your profile gets stuck, then your ISP will be able to get BT to unstick it.

[mr_chris]

Sorry, yeah I didn't make that clear, was typing quicker than I was re-reading it back.. lol

[setecio]

Just to be clear about this, it's not the ISP who sets the IP profile, but BT - it's an automatic process carried out by the exchange equipment. But if your profile gets stuck, then your ISP will be able to get BT to unstick it.

Is it still done by BT if my ISP is using their own equipment in an Unbundled exchange? If not would the ISP then do a similar thing themselves?

[roseway]

IP/BRAS profiles are a BT thing. If your line is unbundled then as far as I know there isn't any profile. But ISPs can (and usually do) use traffic management procedures which can limit your speeds in various ways.

[Pwiggler]

Grrrrrrrrrr

[mr_chris]

Pretending to be a lion, Mr Wiggler? Or are we just frustrated at the words "Traffic Management"?

Incidentally, sorry to hijack the thread... it reminded me of the attached pics I took a long time ago. I was walking along next to the tram tracks one day when I spotted this board propped up against the side. I had to take a couple of pics, given it was about the time PlusNet's Premier account was getting traffic shaped, (and they were invariably getting it more wrong than right!). The second pic is a closeup, obviously!

It made me lol anyway

[attachment deleted by admin]

[attachment deleted by admin]

[Pwiggler]

STOP IT CHRIS YOU FOUL MOUTH !!!

i think the words 'traffic shaping', 'traffic management', juniper and ellacoya should be added to the swearing filter on the site 

[kitz]

[tnp]

AS I understand it, the BRAS profile is set to prevent the downstream data flooding the DSLAM. So its a bad idea not to have it. Its SUPPOSED to throttle the channel coming over the backhaul so that data arrives at the DSLAM comfortably below the level the DSLAM can pass it on to you.

One of the things that has happened fairly recently is that TCP/IP windows sizes have gone up.The TCP/IP windows size is the maximum total amount of data in many packets that can be sent before the sender will stop and wait for an acknowledge packet, saying its got there OK (or not).

I believe - don't take this as gospel - that some sites and PCS - especially running later software, will negotiate this up to 32Mbytes.  So a site might send yoy 32Mbyte - whchj i MAY secods worth - befor exepecting a reply.

If the ADSL line cannot absorb that, it has to be stored somewhere.

BT's DSLAMS can't do that. SO the BRAS profile is set to presumably throttle it back so that the ISP has to buffer it themselves in THEIR kit.

So lets say you are talking to a big mother of a server bang on the UK backbone connected at gigabit speeds to your ISP, and you are running a super hot machine with the latest TCP/IP stack and all the routers in between are latest spec. you start to download a file, open a connection, and every machine says '32Mbytes window? Yup. I can handle it!'.

So the server take that file and spits out a 32Mbyte chunk and waits for a reply from your end saying 'I got some/all the packets in that'..

The server will keep up with the acks being received to the point of always being 32Mbytes ahead of what its got back as acks.

So somewhere in the chain those 32Mbytes are sitting in a queue waiting to be forwarded on.

BT simply says 'we will not buffer: if you send us more than we can get down the users line, we will throw it in the trash can'. So BRAS is passed back by the system to I THINK the ISPS IP-to-ATM kit, and it gets buffered there. OFF BTS ATM and DSLAM kit.

I an ideal IP only world, TCP/IP should negotiate the window size to match whats going on in between, BUT in the name of cheaper kit, it doesn't..because several of the links in the chain are not running TCP/IP at all. Essentially TCP/IP stops at the  port of your modem, and reappears at your ISP.  BRAS makes sure that what is happening in between behaves like a rate limited IP line, not the superfast ATM and the rather grotty ADSL that it really is.

[setecio]

I just wanted to come back and check this.

Imagine someone had a faulty router for 6 months and had only been getting 512 broadband download speed on a line which would get 4Mb speed with a properly functioning router.

They then bought a new properly working router and plugged it in. Would the router immediately sync at around 4Mb even though the download speed might be limited by a stuck BRAS profile.

The question is basically .... is it easy to tell from a (properly functioning) modem sync speed what the current connection should be, or can the modem sync speed be limited by something similar to a stuck BRAS profile ?

Thanks.

[roseway]

In those circumstances the new router should connect at ~4 Mbps, and the IP profile should rise automatically within a day or two. If the profile doesn't rise within (say) a week, then it's probably stuck and you would need to ask your ISP to get it unstuck for you.

[setecio]

Yep, I'm just checking that nothing restricts the modem sync speed and I can therefore always look at the modem sync speed knowing that nothing in BT or ISP can be limiting that figure from what it should be.

If so then I can always look at a modem sync speed and see if I'm getting what I should be getting.

I'm pretty sure the answer is that there isn't anything that can stop the modem sync speed from indicating its true value and I wouldn't have to ring BT to get them to remove any limiting system which would make it show a lower value.

Hope I'm explaining this.

From what I've read it appears that the modem will sync with the exchange and that sync speed is indicated if I log into the router. I just want to be sure that I can look at that figure in my modem as a guage to what my speed should be ..... and know that if I can only download at 512 and look in my modem and see a sync speed of 512 then I know the slow speed is either all I could ever get or due to a pysical problem but NOT due to a stuck BRAS profile ...... whereas if I look in my modem and see it syncing at 2Mb then it could be a stuck bras profile.

So to answer my question I'm hoping someone will confirm that a stuck BRAS profile does not affect my modem sync speed, and nor does any other metering or limiting device in the exchange. .... ie a modem is always free to sync and not restricted by something similar to a Bras profile.

[Ezzer]

If your on a rate adaptive broadband (ie up to 8mb) then based on the combination of you attenuation loss & snr the system works out a theoretical maximum speed & typicaly gives you an actual connection of approx 0.5mb slower back to the exchange. This is monitored for 10 days after a new service has initaly connected (or after a fault has been closed) you spped might be tweeked a few times before it finally settles.

If your connection to the exchange is one speed yet your getting 0.5,0.25, 0.12 mb approx then you've been throttled back & yes between your isp & BT wholesale this can be removed. BUT! the service would have been throttled back for a reason, ther would have been some "events" which ment the quality of signal dropped significantly for some periods of time. Unless this has been cured then chances are you'll end up been throttled back again at some time.

It's a bit like driving on the motorway when you know you can do 70mph. but you just thought "Woh was that black ice i felt there... I'll drive at 20mph to be on the safe side until I'm confident the road conditions are ok"