Tot And Tt&t

[Phil Conners]

I have two phone lines, one from each of TOT and TT&T. The TOT line does not have ADSL enabled, only the TT&T line, and I use Maxnet with it.

By accident I plugged my router into the TOT line today and ... surprisingly it worked (with Maxnet).

the line quality settings are quite different:

TOT: Down Up

Noise margin 21.2 14.0

Output power 18.6 12.4

Attenuation 46.5 31.5

TT&T: Down Up

Noise margin 30.2 24.0

Output power 13.9 12.3

Attenuation 22.0 12.0

Note the big difference in the values. Seems to me the TOT line is the better line, right? Does that have any significance?

Repeated speed tests seems to indicate little or now difference in up/download speed so perhaps it's not important?

[monty]

Hi Phil,

Nope, the TT&T line is definately better

Attenuation should be as low as possible, this is the amount of signal you lose on the line.

ToT =46.5 and TT&T is only at 22, indicating that the TT&T exchange is much closer to you then the ToT exchange!

Noise margin on the other hand should be as high as possible. The higher the margin, the better the modem can distinguish between the actual signal and the noise the line picks up along the way! Also called the Signal to Noise Ratio (SNR).

You shouldn't see any difference in speed, since the numbers indicate that both lines could support speeds of over 1024 kbps...

The sharing happens at the ISP (Maxnet) where their routers will decide how big a pipe you will share with how many users. The TOT and TT&T lines are only conduits to the ISP, and they both support higher speeds then what the ISP is willing to give you!

[Phil Conners]

Hi Monty, I kinda had a feeling you'd be the one to reply

Thanks for the clarification. Funny that it works at all through the TOT line (which isn't explicitly enabled for ADSL) isn't it?

[Naam]

"By accident I plugged my router into the TOT line today and ... surprisingly it worked (with Maxnet)."

AMAZING THAILAND! i too happen to be on Maxnet and TT&T and got recently (for a fistful of dollars) an additional TOTline to be used as a back-up with a different IS-provider in case Maxnet causes problems again (big problems in the past).

will try later to plug in my modem/router into TOT and see what happens.

my values vary a lot. presently:

noise margin downstream: 19 db

output power upstream: 13 db

attenuation downstream: 61 db

noise margin upstream: 26 db

output power downstream: 11 db

attenuation upstream: 31 db

i don't realize too much difference in speed when attenuation is bad but it slows terribly down when downstream noise margin drops below 12.

used to be on 1024/512 which was much slower than my present 512/256.

[monty]

Dr. Naam,

Seems like you are on the absolute distance limit away from your exchange! As a rough guess I would place your distance from the exchange to be between 5 and 7 km.

The noise margin is right in line with the attenuation and the speed you get.

With an attenuation of around 60db, you can expect the snr (= noise margin) to drop below acceptable levels when the modem tries to connect at anything higher then 512kbps.

You'll see that right after you reboot the modem the snr will be a bit over 20, to then drop to a lower but stable level (between 15-20db).

On these marginal lines, it'll depend a lot on how good your modem can handle the noise, and wether it can seemlessly reduce the connection speed to keep acceptable snr levels. (the lower the speed, the higher the snr, hence the upstream levels, normally at half the speed of the downstream, always will show better snr)

You are absolutely correct in saying that the attenuation does not affect speed, but low snr levels do. With a low snr there will be so many errors in the transmission that results in half your speed being eaten up by your modem requesting data to be sent again, as well as downloads being corrupt after completed...

Unfortunately, TT&T can do jack all for your problem, since it's noise picked up along the way which is deteriorating your signal. Simply a faulty transformer for a neon light somewhere in the vincinity of where your line runs can completely stop your modem from connecting!

This is simply a major drawback form the lines being strung between the poles, as opposed to the underground lines we are used to in the west...

So in short, you are not experiencing problems with your ISP (Maxnet), but with your ADSL line provider (TT&T). These are two different things, and although Maxnet is owned by TT&T (it was originally set-up by Ji-net for them), they are two completely different departments. Switching for example to Csloxinfo as an ISP using the same TT&T line will not make any difference at all!

Just shoot of a prayer that the TOT exchange is closer to your house then the TT&T one

Edited October 27, 2006 by monty

[Naam]

"On these marginal lines, it'll depend a lot on how good your modem can handle the noise, and wether it can seemlessly reduce the connection speed to keep acceptable snr levels. (the lower the speed, the higher the snr, hence the upstream levels, normally at half the speed of the downstream, always will show better snr)"

*****

thanks a lot Monty for your informative answers. as far as modem-routers are concerned i was under the impression that there is no difference. but my Surecom modem was fried by lightning (as was the motherboard of my main PC) and now i'm on Zyxel P-66OH which seems to render a better performance. but that might be just my subjective view as the speed varies a lot depending on the time of the day. could you comment on that.

p.s. haven't tried out the TOT-line yet because i was too lazy to move my desk

[monty]

Hi Dr.,

There's several factors determining how good a modem (actually the chipset used by the modem, several diferent brands of modems might use the same chipset) will work on a marginal line.

First is the sensitivity, meaning the more sensitive your modem, the lower the SNR ratio can be without getting transmission errors.

Compare it to a radioreceiver, the more sensitive radio will still get reception in remote areas, whereas an el cheapo radio will pick up nothing but noise!

The second is the firmware controlling the chipset. It's the firmware which will force lower your connection speed until a usable snr ratio is reached. A good written firmware will be able to drop speed a bit in order to keep connected without you even noticing it.

I've seen modems just stay connected with a very low SNR, resulting in almost total loss of data transfer, without even attempting to go to a lower speed.

So yes, there definately is difference between different modems when used on marginal lines

[Naam]

"The second is the firmware controlling the chipset. It's the firmware which will force lower your connection speed until a usable snr ratio is reached. A good written firmware will be able to drop speed a bit in order to keep connected without you even noticing it."

*****

thanks again Monty. all that modem tech is uncharted territory for me and it was of no interest when i had a 5mbit connection where speed variations were not or hardly noticeable. now of course -being on "amazing thai" snail speed- each and every little improvement counts.

question: what kind of information is available (if any) concerning the 'quality' of firmware? i checked Zyxel's website which shows that there is an upgrade -dated end of august- available but i have of course no idea from what date my present firmware is. i bought the modem only 10-12 days ago.

n.b. i have also no idea how to load/replace the firmware. learned only a few weeks ago by trial and error how to set the basic parameters in the modem/router with the cold sweat running down my back. was fed up with my local "expert" who refused to explain anything so i kicked him out and now i'm on my own.