Topic: filters

[Baz]

just been swapping my dangly thing  for a faceplate...........know what I mean

anyway could someone explain what line attenuation and noise margin figures mean. What are good bad?

figures from my router are.........with dangly filter I had

line attenuation of    37.0db down and 18.0db up,
noise margin            7.9db down and 19.0db up


with faceplate I have

line attenuation of        37.0db down      18.0db up
noise margin                7.3db down        23.0db up

is this good or bad I have no idea.

[Simon]

I shamelessly stole this from another forum, but so did the original poster    so here goes:

The following may help. It is not my research but was posted some weeks ago by someone whom I neglected to identify.

Noise Margin (AKA Signal to Noise Margin or Signal to Noise Ratio)
Relative strength of the DSL signal to Noise ratio. The higher the number the better for this measurement. In some instances interleaving can help raise the noise margin to an acceptable level.

6dB or below is bad and will experience no synch or intermittent synch problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with little or no synch problems* (but see note below)
20dB-28dB is excellent
29dB or above is outstanding

* Note that there may be short term bursts of noise that may drop the margin, but due to the sampling time of the management utility in your modem, will not show up in the figures.

Line Attenuation
Measure of how much the signal has degraded between the DSLAM and the modem. This is largely a function of the distance from the exchange. The lower the dB the better for this measurement.

20dB and below is outstanding
20dB-30dB is excellent
30dB-40dB is very good
40dB-50dB is good
50dB-60dB is poor and may experience connectivity issues
60dB or above is bad and will experience connectivity issues

DSL Rate ***/tx/rx/Rate
The actual service data rate that your ISP has provisioned.

Attainable Line Rate
This is the maximum rate at which your modem can connect to the DSLAM if there was no service provisioning limiting the bandwidth. The higher the number the better.

Occupancy
Occupancy is the percentage of line capacity used. Each DSL line is capable of a certain maximum speed or "capacity" dependant on line distance and other varying factors. The occupancy is an expression of your current sync rate setting over your maximum capacity. There are occupancy rates for both upload and download. The lower the figure, the better. Because of error correction and other factors in the DSL protocols, a margin is required so that a connection can be maintained under varying line conditions. If the occupancy approaches 100%, any interference can cause the ADSL sync to be lost. A useful measurement to monitor when sync problems occur. [AFAIK the billion SNMP utility does not give a direct measurement of occupancy :-( ]

(with due acknowledgment of the other sources/forums that this info was gleaned from)

[Baz]

cheers Simon, so it seems that my line attenuation is excellent range but noise margin is just fair but a bit confusing that it went down slightly for downstream and up quite a bit for upstream after fitting the faceplate which people say should improve things.

[Simon]

Well, your upstream is just as important as your downstream, so you may still find that it balances out to a more stable connection.  If it works, and you're happy with the speed and stability, I wouldn't pay too much attention to the numbers, but obviously, they are useful for diagnostics, should you have any problems.

[Baz]

great thanks again Simon.

[Rik]

Coming to this as a Johnny come lately...

The 'gradings' for noise margin appear to date from pre-Max days. Nowadays, a BT-provided line will have an initial target noise margin of 6db, this will only increase either to gain stability, or if maximum sync speed is achieved with some room in hand.

To the OP, without knowing your sync speed, the figures don't mean a lot. Your noise margin hasn't changed much with the filtered face plate, but if your sync speed has increased significantly, then it's been worthwhile fitting it.