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    Sync rate Issue

    This is a discussion on Sync rate Issue within the Sky Broadband help forums, part of the Sky Broadband help and support category; HI all, Weird one for you I have syncing successfully at around 2300 for well over 2 weeks with no ...

    1. #1
      boab2791's Avatar
      boab2791 is offline Sky User Member
      Exchange: Lennoxtown (WSLEX)
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      Router: Non Sky Router
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      Milton Of Campsie
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      Sync rate Issue

      HI all,

      Weird one for you

      I have syncing successfully at around 2300 for well over 2 weeks with no drop outs and I have a target SNR of 15db at the exchange due to initial problems. I have used the DMT tool on my 585v6 to lower the target which seems to get as low as 9db, this usualy gets me the 2300 sync.

      Anyway I was out of the house for 2 days and when I got back the router had resync'd to 3338 albeit with 0db SNR down and no actual connectivity to the Net. I assumed the line monitoring system at the exchange lowered my target SNR back to defaults as I had been successfully connected with no dropouts and was getting 2 meg download throughput which I am happy with considering my line attenuation of 63.5db. While connected at 2304 my interleave FEC error rate was roughly 20000 for every week connected I think.

      Now the strange part, I had to reset the router, and it now will not connect above 1500 and the bizarre thing is the FEC error rate has shot through the roof, in over 13 hours of being connected the error count is 5,012,830 yet the higher sync I get the lower that number becomes.

      I have tried sveral times over the past few days to get my sync back to 2300 with no success and I am puzzled as to why. I am currently connected at 1472 with 10.5db SNR down. I'm also seeing quite a few CRC errors which I did see on the higher sync rate.

      I am connected directly to the master socket which has a pre-filtered BT faceplate attached if that's any help.

      Can anyone suggest any reasons for this.

      Thanks in advance for any help given.


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    3. #2
      Saturday's Avatar
      Saturday is offline Sky User Super Mod
      Broadband ISP: Sky Broadband Unlimited Pro
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      You are on Connect.

      BT have issued clear advice to ISPs on the use of tools to manipulate line rate and noise margin. To quote: "this bypasses DLM and could cause very serious performance issues".

      My guess is there would be some justification for the warning?

      With ADSL Max (Connect) rate adaption is handled by RAMBo at the exchange. RAMBo is made up of two parts - MAX and DLM. MAX monitors the line rate and adjusts BRAS and also notifies BBCR of any changes in the BRAS profile. DLM analyses the performance statistics for the line DSLAM and adjusts the line profile.

      MY guess is that if DLM sees a noise margin change then this results in a rate change which will be passed to MAX which will adjust the BRAS profile. The router has to agree a downstream rate with the DSLAM for a given noise margin. However, if the router is "locked" to a high noise margin then maybe the balance between MAX and DLM is screwed up?

      I should stress that this is pure conjecture on my part. I'd be really interested if anyone has a more solid technical understanding than I have and can explain exactly what would/does happen.

      I think your best recourse is to return your router to default state and get on to Sky Technical Tier 3 to ask them to re-profile your line.

    4. #3
      Keiran2K8's Avatar
      Keiran2K8 is offline Skyuser Serial Spammer
      Exchange: Redditch
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      Sorry to be a annoying but ;

      That has some if not all you need to know about Connect!

      @Saturday! Feel free to add to it?



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