Interleaving - worth asking for?

A struggling Draytek 2600 earned me a 12dB target margin after a couple of months.

A replacement router base on TI AR7 chipset synced faster but snr graphing showed early morning drops to 3dB all the time and even to 1dB on one occasion.

I got a Speedtouch 585 so I could use DMT. Tweaking margin down to around 8dB gave me a sync that supported 6Mb/s easily.

Out of the blue one Saturday afternoon the router resynced for no apparent reason and I was getting 8128 sync with 6dB margin. I have since removed the tweaking going back to default and it is still 6dB margin. I have no idea what caused either the resync or margin reduction.

The problem I see now are high numbers of CRC and HEC errors (never any FEC). Sometimes at night I see 600 or more errored seconds in the last 15 minutes reported. This seems to lead to timeouts sometimes and stutters in speed which are noticeable when simply surfing (ok I guess it could be contention too).

I recall reading that interleave does not fix all error types but have no idea what it does help with and what it doesn't. So...

Is it worth asking for interleave to be turned on or should I try tweaking to increase the margin a tad? Bear in mind that talking to the ISP will be a real pain as I'm currently with AOL.

here is a good link by John, one of the site's founders with an explanation of inteleaving;

Explanation of Interelaving

I would try tweaking your SNR up slightly first to trade a bit of speed for stability, as you will lose a bit of speed with Interleaving anyway.

AOL now enable it by default, so someone there should know what you're on about

I would enable it, earlier in the year I was working on 3 lines in the same place and the one that got interleaved always had the best throughput and the lowest error rate. In about 10 hours this line at 9.5 dB margin clocked up :-

LocalInterleavedChannelFEC = 9737
LocalInterleavedChannelCRC = 7
LocalInterleavedChannelHEC = 5

and its typical to see interleaving solve >90% of the errors. 600 errored seconds in 15 mins is 2/3 the time with errors, so that's fairly bad.

Thanks for the link - I'll give it a read. A quick look seems to indicate it's abbout the technicalities of how it actually works - I guess I could give wikipaedia a viewing too on that. It was practical experience I was looking for more though.

Yes that was my suspition after seeing stats posted by folks who'd been upgraded or provisioned by AOL.

Maybe it is a good idea - could cut down on problems and support calls.

During most of the day mine is actuallly fine - the errors start piling up during the hours of darkness so I still think it's MW radio. DMT doesn't show many absolute gaps even when resynced when it is erroring.

I'm not 100% certain that the slowdown and stutters are caused by the errors - a friend on bully has the same router on their 16Mb/s and he tells me that it is subject to inexplicable slowdowns when hammered which clear with a reboot. Certainly rebooting mine last night cleared the slowdown even though I still saw errors.

I've decided to reboot it every morning to retain maximum sync speed and hopefully clear out the likely memory shortage caused by a firmware bug. It isn't the NAT tables as they look fine in the stats and I dont run torrents and the like very often anyway.

I'll decide on whether to face AOL with a request for interleaving when I see how that regime pans out.

I'm a gamer & had interleaving applied to my line (turns out that a BT fault - degraded cable in distribution point was to blame, might even get it taken off now that fault has been resolved) - it's added 9ms to my ping. Not bad and in practice pretty much not noticed.

Certainly the latency doesn't bother me as I'm not into gaming.

Had another couple of spells of high error rates last night spotted by looking at router stats when I started getting timeouts on websites. Overall error rate looks good but I was hitting around 400 errored seconds in last 15 mins on this occasion which basically just killed it to all intents and purposes. About 5 mins later it was fine again until the next episode. There were some thunderstorms around but the errors lasted several minutes - plenty of time for me to get the timeouts and check the router numbers.

Will be phoning this morning to get interleave turned on and see if that sorts it.

=====

Very pleasant young Irish girl, listened attentively to the problem and what I wanted. Then admitted she didn't have a clue what interleave was and spoke to her supervisor who obviously didn't have a clue either. At least she promised to pass the request on to somebody in tech who might. I'm not holding my breath.

Edited by kwikbreaks (Thu 14-Sep-06 11:15:59)

> AOL now enable it by default, so someone there should know what you're on about

I just love optimists. Second call to enquire on progress - they couldn't even tell me what I'd asked for as the call log was just a load of rubbish. After being cut off waiting for their "technical fault department" who the first bloke tried to transfer me to I told the second one to write down exactly what I wanted ie ask BT to turn on interleaving and make sure the request was passed to someone who understood what was meant. I also told them I was going on holiday soon for a fortnight and if it wasn't done when I got back that my next call would be to request a mac.

Any ISP recommendations folks?