[AusNOG] Strange ADSL problem - troubleshooting / diagnosis advice wanted

[Jarrad Mitchell]

I'm not sure if it has been mentioned or not as I just joined, but VDSL2 supports Vectoring, which as I understand it is basically scheduling transmission across the different pairs in say a 100 pair bundle.  This way, cross talk based interference is run.
Quote Paul:"VDSL2 doesn't really add much functionality to ADSL2 other than the vastly expanded frequency range."
'Frequency Range' literally means Bandwidth ;)  How much data you can transport over that - the Bitrate, which is what us IT folks generally mean when we say 'bandwidth' - really just comes down to how clever you are with math.  
For Example:Interleaving in ADSL2 allows you to dedicate less of your bitrate to error correction, and hence make available more bandwidth.
Vectoring in VDSL2 allows the DSLAM some control over how much noise each pair will be subject to.  Imagining we have Pairs A,B,C,D in a flat ribbon.  Vectoring would ensure that Pairs A&C and B&D Transmit at the same time, but never A&B and C&D.  Because of this, each individual pair is subject to less crosstalk, and hence more bandwidth is usable over the same physical medium, and a higher bitrate can be achieved by increasing the width of your modulation scheme (eg, moving from 256 Bins to 512 Bins as in ADSL2->2+) or changing the complexity of your scheme (eg, ADSL1->ADSL2).
Sorry If I've repeated someone,
Cheers,
Jarrad

Date: Fri, 12 Sep 2014 18:03:52 +1000
From: pbrooks-ausnog at layer10.com.au
To: ausnog at lists.ausnog.net; jeremy at visser.name
Subject: Re: [AusNOG] Strange ADSL problem - troubleshooting / diagnosis advice wanted


  
    
  
  
    On 10/09/2014 3:28 PM, Jeremy Visser
      wrote:

    
    
      On 10/09/14 14:39, Paul Brooks wrote:

      
        ADSL2+ is supposed to re-train to a new sync rate seamlessly without
packet drops, whereas the older ADSL1 had to effectively drop the
line, re-sync, generate a new bitfield table per tone to cope with
changes to background noise and cross-talk that caused a need for a
re-sync.

      
      I thought that was a feature of VDSL2, not ADSL2+.

I’d be interested to see a source on that as happy to be wrong.
    
    

    Its actually goes back to ADSL2:

    

    G.992.5 Jan 2009  ADSL2+

    

https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.992.5-200901-I!!ZPF-E&type=items

    

    

    Page 'ii':

    This Recommendation defines several optional capabilities and
    features:

    – transport of STM and/or ATM and/or Packets;

    – transport of a network timing reference;

    – multiple latency paths;

    – multiple frame bearers;

    – short initialization procedure;

    – dynamic rate repartitioning;

    – seamless rate adaptation;

    - extended impulse noise protection;

    - erasure decoding;

    - virtual noise;

    - impulse noise monitor.

    "

    

    G.992.3 April 2009 ADSL2:

    

https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.992.3-200904-I!!ZPF-E&type=items

    

    Page 'ii':

    "This Recommendation defines several optional capabilities and
    features:

    • transport of STM and/or ATM and/or Packets;

    • transport of a network timing reference;

    • multiple latency paths;

    • multiple frame bearers;

    • short initialization procedure;

    • dynamic rate repartitioning;

    • seamless rate adaptation;

    • extended impulse noise protection;

    • erasure decoding;

    • virtual noise;

    • impulse noise monitor."

    

    "Relative to Recommendation ITU-T G.992.1, the following PMD-related
    features have been added:

    • New line diagnostics procedures available for both successful and
    unsuccessful initialization

    scenarios, loop characterization and trouble-shooting.

    • Enhanced on-line reconfiguration capabilities including
      bitswaps and seamless rate adaptation.

    • Optional short initialization sequence for recovery from
      errors or fast resumption of operation.

    • Optional seamless rate adaptation with line rate changes
      during showtime."

    

    Clause 8.16:

    "8.16 On-line reconfiguration of the PMD function

    On-line reconfiguration of the PMD function is intended to allow
    changes in the control parameters

    without interruption of service and without errors (i.e., bitswap,
    dynamic rate repartitioning and

    seamless rate adaptation)."

    

    VDSL2 doesn't really add much functionality to ADSL2 other than the
    vastly expanded frequency range.

    

    cheers...

    

    Paul.

    

    

    

    

  


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