Can someone explain why this happens

I've been testing my routers sync to the exchange, and was considering moving the router to get the best possible sync by plugging it in directly to the master socket, but I have a strange issue that I can't explain

The router normally sits in my office and is on the end of good quality telephone extension wire that weaves it's way under floor board and up walls, and is probably 15 metres in length by the time it reaches my office

When the router is plugged in to this extension, it syncs to the exchange at about 19750 downstream and about 828 upstream

When I plug it in to the master socket (disconnecting all extensions), the router syncs at about 17000 downstream and 1000 upstream

When I return everything back to it's original position in the office, the router syncs back at 19750 downstream and 828 upstream

I have tried this several times and when moving the router to the master socket the downstream sync drops and the upstream sync increases

The thing that is puzzling me is that when plugged in to the master socket, I would expect the best up and down sync, but the downstream decreases but the upstream increases

Can any one explain this behaviour to me?

Could be a bad source of noise close to the master socket, or your wiring is not how you expect, i.e. the master socket is actually an extension.

When using the master socket, are all other sockets in the house dead, i.e. a filter and phone do not work?

It's definitely the master socket as BT put it there last year

I removed the front plate and and plugged the router directly in to the test socket

as you increase frequencies in a wire, you start seeing more and more the effect of tuning of the wire length to the frequencies involved. I don't want to give the impression I understand this fully, but you need to change the length of a radio antenna to match the wavelength, or half/quarter/two wavelength etc to get best reception. Normally when extensions are used they are flat cables which means not twisted. Twisted is the best way to stop cross-talk (interference) between the wires. Flat is the worst and maximises the cross-talk.

My hypothesis is that your high quality extension is twisted, and adds just the right length to tune the wire for the higher frequencies of ADSL2+ broadband, giving you that extra boost in the top end.

If you can get the list of bits per channel (per DMT tone) from the home router in each location, it may shed more light on if it is the top end data rate that increases (adding weight to my hypothesis) or if some mid-range band is drowned out....suggesting a local noise source is the issue.

Or just plug it in where u get the best outcome and sit happy )

In reply to a post by ntm1275:

It's definitely the master socket as BT put it there last year

I removed the front plate and and plugged the router directly in to the test socket

And when the router is connected to the test socket, do phones work in any of the other sockets in your house, particularly the one in your office where the router is usually connected. I know you say it is a master socket, and it obviously looks like one, but with tracing the wiring from where the BT wire enters your property, it's hard to say for sure.

Hi, Myth is exactly on the right lines here... But it is more complex due to the large number of different frequencies used by ADSL or VDSL connections...

With a single frequency on a cable or twisted pair, as in the case of a telephone line, there are certain lengths which are odd multiples of a quarter wavelength of the frequency where the cable performs like a filter.

With the (hundreds) of tones used with xDSL, the effect is not usually seen to the point that it matters - there are always some tones that perform less well - but there are certain line lengths where a few tones show the problem and a lower sync speed is seen.

I have the exact same issue on my primary telephone line (before it was converted to an 80/20 FTTC connection) where the router connected slightly faster when on an extra 30m or so of cable, regardless of if it was cat5 or BT extension cable.

You may well get the better speed with a longer (or shorter) cable at the master socket - but trying to find a cable length that improves the speed is very hard as the DSLAM will soon get fed up of the repeated disconnections and raise the target SNR...

Bottom line is that xDSL is more like shortwave radio in its behaviour on the PSTN line - and that's why multiple extension cables tee'ed after the master socket reduce sync speeds as they each look like an "off cable stub" which forms a filter at multiple specific frequencies. Many joins and tee's makes many filters, hence the benefits of a filtered master socket and a clean unfiltered pair to the router - even if it's quite a long way.

Yes all phone lines in the house go dead when the front panel is taken off the master socket

UPDATE

I've bought a ADSLNation XTE-2005 faceplate filter from BroadbandBuyer and all my problems are now sorted

Router now syncs at 20014 downstream and 1020 upstream

Pings are lower as well

The thing I like about it as well is that it has separate connections inside to have filtered and unfiltered extension wiring

Now a happy chappy

Does anyone know what the maximum downstream and upstream sync rate is for Talk Talk ADSL2+ LLU up to 24meg?
Just want to see how far I'm off the maximum, but I'm definitely happy with my current syncs

Rebooted the router again and it's gone up to 20139 downstream - getting better all the time

Edited by deleted (Mon 23-Apr-12 18:31:30)