An error correction algorithm that makes an ADSL line more immune to the odd incorrect ATM cell.

It adds a little latency, so gamers may notice it, if they are very twitchy

Andrew

Does this Forward error correction service really add such substantial latency? Surely congestion is going to be a much bigger cause of delay.

Interleaving should prevent retrasmissions and the subsequent reduction in windowing size as well as dropped packets so surely there are substantial benefits.

I know that with ADSLMAX interleaving is is an alternate datarate profile so if you cant have say 5.5meg, the DLM system will try 5.5meg with interleaving, if it cant do this then it will drop you to 5meg, then meg with interleaving and so on.

surly it would be better to have 5.5meg with interleaving than 5meg without?

"surly it would be better to have 5.5meg with interleaving than 5meg without? "

The answer will vary according to the degree it is needed. Since Opal apply it by default end-users don't get the choice.

How much latency does the interleave depth Opal use add? Max its around 15ms, but depending on the depth set it could be 2ms through to 40ms.

Interleaving adds an overhead of 512kbps and doubles the latency. That means it reduces speed (not sync) by 512kbps and increases ping times from ~14mS to 28mS. So unless it is needed to stabilise an error prone line, interleaving is better kept switched off. A good explanation is here.

Are those figures TalkTalk LLU specific or just the BT Wholesale Max implementation.

Andrew

In reply to:

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Are those figures TalkTalk LLU specific or just the BT Wholesale Max implementation.

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From my limited experience the TT LLU interleaving seems to behave the same as BT ADSL Max has been described. For instance my maximum download speed is 512kbps short of the theoretical maximum and my pings at 28mS are twice what I would expect. The interleaving standards (trellis correction) would have to be universal because the TT service is ADSL1 and works with different end user devices (I am using a Zoom PCI modem). I have also noticed that at 8064 sync my interleave depth is always 64 (the maximum) with the upstream at 2. When I had a higher target noise margin and lower sync speeds, the interleave depth would be less. Therefore I think TT has interleave set at various levels in its users' profile whether it is necessary or not. I will find out when they manage to turn it off!