What are the downsides of interleaving on ADSL / VDSL2 connections?

g67575

g67575

g67575

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My line has recently had some interleaving applied to it recently by BT's DLM system.

Does this matter? The only thing I've noticed is higher connection latency. When pinging bbc.co.uk, the latency was about 11ms before interleaving (Path mode was 'Fastpath'), and around 25ms with interleaving enabled on the upstream and downstream.

What's the reason interleaving isn't enabled by default on most lines?
 
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It is also enabled by default on a new line or change of provider, it may or may not be removed by DLM depending on numbers of errors.
 
You'll generally get higher stable bandwidth with interleaving on vs fastpath - though it will lower bandwidth vs a stable line obviously.

The only disadvantage, if it is needed to keep the line stable at a higher level of bandwidth than max stability with fastpath is for fast paced online gaming.

Even that can be a bit subjective - some people will notice it more than others and for some 1 depth of interleaving the more consistency latency might be more desirable than the higher variation with fastpath. But higher interleaving depth even more casual players will notice.

I had a long conversation on this with someone from BT's executive level complaints team once - turns out quite a few of them are gamers - which is part of the reason they don't just chuck everyone on interleaving and call it a day. (I was about 25 at the time and talking to a women who sounded in her 50s or so and held a highly professional role in the company, talking quite enthusiastically and knowledgeably about Quake was a little surreal).
 
I was wondering, so do FEC errors only occur when interleaving is enabled?

I seem to be getting a lot of FEC errors since interleaving was enabled recently on my line.
 
FEC is a way of encoding data with extra redundancy - hence higher latency and lower bandwidth - when that encounters too much noise to reliably send data you get an FEC error.
 
My router rebooted and resynced at a higher line speed today (undoing any changes I'd made):

resync.jpg


So, it looks like the interleaving is helping a great deal on my line, and might even allow the line to sync at around 72mbps (downstream). Assuming that's true, I might have to find out how to manually apply interleaving via SSH commands.

There's quite a lot of FEC errors on the line:
https://i.ibb.co/R9G2wMt/Capture.png

I have a theory that the DLM system may be increasing the interleaving if it detects a large increase in the number of Upstream / Downstream FEC errors, is that possible?
 
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From a quick google you are currently 1 below the maximum interleave depth on the downstream, you should stop using that asus router :cry: i used a asus dsl-n66u briefly and my fttc line that was 15.5mb/0.7mb on a decent broadcom chipset, could only get 10mb/0.7 on the n66u which uses a mediatek chipset same as yours, have a look at this thread on here that deals with another asus router with the same garbage chipset https://www.overclockers.co.uk/forums/threads/anyone-using-an-asus-dsl-ac68u.18606945/

There are a few other lines of enquires on getting the most out of your line, google quiet line test and do one, second whats your internal wiring like? you have the router connected to the master socket not on the end of some dodgy extensions.

I am still puzzled to what problem you are having you don't seem to care about latency, was it frequent disconnects? or you trying to achieve the best sync on the line?
 
I don't mind higher latency much, I'd like the line to be near 100% reliable (ideally no errors / data loss), with a reasonably high downstream sync rate.

Your line shouldn't be capped unless you are getting a lot of CRCs or 'Errored Seconds', or disconnections. I switched the router/modem because my fairly new broadcom based kit was bouncing between high syncs at 3db, to lower syncs at 6db, both had plenty of line errors.

The Asus router/modems have a lot of options that can improve the line statistics, which in some cases can lead to improved line sync rates. They also have very good firmware + web interfaces.

I've tried lots of router/modem chipsets over the last few years and people tend to exaggerate the difference it makes, the line length is the main factor that will decide the speed and quality of the connection. Another factor is the type of cabinet, e.g. ECI cabinets do not support G.INP.

The line still seems to be getting some CRC errors with interleaving, but it does seem to help. The only thing I've found that works is disabling the D3 downstream band, which can be done quite easily via Telnet or SSH. Disabling the D3 band also seems to reduce the interleave depth.
 
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