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    Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband

    This is a discussion on Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband within the General Computing and Internet forums, part of the Community channel category; Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband - ISPreview UK Earlier this year BTOpenreach confirmed ( here ...

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      Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband

      Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband - ISPreview UK
      Earlier this year BTOpenreach confirmed (here) that they were deploying Physical Retransmission ReTX (G.INP – ITU G.998.4) technology to improve the performance of their ‘up to’ 40-80Mbps capable Fibre-to-the-Cabinet (FTTC) lines. But at least one ISP has noticed that this is also increasing latency times by around 15ms (miliseconds).

      The G.INP technology is essentially an error correction solution that can help to tackle spikes / bursts of Electromagnetic Interference (impulse noise), which makes some problematic lines more stable and less prone to errors (Sky Broadband already uses G.INP on their LLU network).

      An Openreach Spokeswoman told ISPreview.co.uk (Jan 2015):

      Openreach is in the early stages of introducing G.INP correction, also known as Retransmission, for FTTC lines that we think can benefit from it. Retransmission supports our Dynamic Line Management process and will benefit customers by providing a slight improvement in speed on FTTC lines where it has been used. It will also improve the volume of FTTC lines running error free.

      FTTC lines will automatically accept Retransmission policies. Those currently with non-Retransmission compliant modem firmware will be identified by management systems and updated, after which Retransmission will become available.

      An upgrade process has started which is expected to take several months to complete.”
      In keeping with this the ISP Andrews & Arnold (AAISP) has noticed a number of FTTC lines drop and reconnect with G.INP enabled and an accompanying “increase in latency of around 15ms“. Latency is a crucial measure of the time (delay in milliseconds [1000ms = 1 second]) that it takes for a single packet of data to travel from your computer to a remote server and then back again (ping).

      In the grander scheme of things 15ms might not sound like much, although it is especially important for fans of fast paced online multiplayer games that like to keep their latency / ping times as low as possible (experiences vary between games, but above 60ms and you can start to notice its impact through synchronisation delays etc.).

      A rise of 15ms above the line’s existing latency time might also give some FTTC services a similar or worse latency performance than older ADSL2+ solutions (Ofcom’s comparison).

      AAISPs Service Status Update

      We’ve been in contact with BT and it does look like BT are rolling out a new profile on to their Huawei DSLAMs in the local green cabinets. It has been expected that BT would be rolling out this new profile, but we didn’t expect such an increase in latency.

      The profile adds ‘Physical Retransmission (ReTX) technology (G.INP / ITU G.998.4)’ which helps with spikes of electromagnetic interference and can make lines more stable.


      We would hope to have control over the enabling and disabling of this profile, but we don’t. Line profiles with FTTC is managed by BT Openreach and are tricky for us and even BT Wholesale to get adjusted
      .”
      The issue is unexpected since one of the advantages of G.INP is that it should be able to perform its magic without impacting latency, at least that’s what we’ve always been told by firms like Alcatel-Lucent and telecoms operators. AAISP has posted an illustration of the problem (here) and we’ve ask Openreach to clarify.


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      Re: Latency Rise as BT Deploy Physical Retransmission for FTTC Broadband

      G.INP had no adverse effect on my latency (ADSL) when sky introduced it.

      At resync i see both bearer 0 & bearer 1 + ITU G.998.4 in the logs, so it is active.

     

     

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