Hi all,
I have received some more questions about line stats;
So what actually determines your broadband speed is something call the
sync rate, which is how fast your modem in your house and the DSLAM on
the other end of the telephone line in the exchange are happy to
communicate at. The content of my talk relating to your BT cabling etc
were all tips towards inproving the sync rate on your line.
The main factoring in determining your sync rate is your telephone
line length from the exchange to your home. The longer the line the
higher the attenuation (so this means the signal is getting weaker as
it travels a longer distance).
If you log onto your router/modem at home you will see various
statistics such as sync rate, signal to noise ratio, attenuation,
output power and receive power.
I have just logging into my router at home and pulled the following
stats from it;
Downstream Upstream
Rate (Kbps): 9214 kbps 695 kbps
SNR Margin (dB): 6.2 8.8
Attenuation (dB): 42.0 22.2
Output Power (dBm): 0.0 12.3
I have a sync rate of 9214Kbps down stream. When your modem boots and
initiates the DSL line it has a conversation with the DSLAM, both ends
measure the noise on the line, and the attenuation (so signal loss
from distance) etc and the DSLAM dictates what the sync rate will be.
I won't be able to get 9.2Mbps because there will be some overhead
room here. I have just done a speed test to
http://speedtest.vostron.net/ and held a comfortable 7.74Mbps download
rate. The sync rate is always slightly lower than what the DSLAM
thinks you line can handle as noise is always coming and going from
your line throughout the day. This means I perhaps could hold a sync
rate of 9512Kbps or slightly higher, but my connection may
periodically drop out when someone in my shared house uses the
microwave or plays soldiers with some walkie talkies. So this is a
safety net to keep your connection up by sacrificing a little bit of
speed.
If your sync rate is too high for the quality of your line you will
experience transmit (and receive) errors on your connection. If you
are experiencing a lot of errors any good ISP (such as Vostron :P)
should after a quick phone call be able to change the stability option
on your line. They can tell the DSLAM to be more reserved and force it
to sync at an even lower rate than it would normally, sacrificing some
speed for stability (we can in fact stage this down several times
putting you down to a "super stable" option which chops 25% (or more)
of your speed off, for stability. You should be able to check for
errors by logging into your router/modem and looking for the error
counters such as FEC errors or CRC errors, Reed Solomon errors and
Drops. Look at these values in relation to the number of packets (or
cells or frames) transmitted and received.
Looking at mine now in the downstream direction, my router has
transmitted 18,698,683 packets and encountered 10,859 errors. That is
not very good, that is roughly one error every 2000 packets. I
currently have an absolutely rubbish router (as I lived in a shared
house, its out of my control!). I have just pulled these from a router
in my office remotely;
Cells: 293077295
Reed-Solomon EC: 0
CRC Errors: 23
Header Errors: 13
A good line like that should only be getting roughyl 1 error in every
million packets/cells. This is a good page about the errors:
http://www.kitz.co.uk/adsl/error_correction.htm
Any good ISP should be able to turn on interleaving on your line to
improve the stability, however this will add on some latency (delay)
to your connection. It shouldn't be horrendeous unless you are a
finanical trader or hardcore gamer, we have plenty of VoIP customers
on lines with interleaving enabled.
This is a good page explaining interleaving:
http://www.kitz.co.uk/adsl/interleaving.htm
Have a read through this page;
http://www.kitz.co.uk/adsl/linestats.htm
And this one:
http://www.kitz.co.uk/adsl/linestats_explanation.htm
They will tell what all your various line stats mean and give you an
indication of what you should be able to achieve. If you are on
ADSLMax (so not ADSL2/2+) see the following link for the various IP
profiles your sync rate is going to be mapped to:
http://www.kitz.co.uk/adsl/IPprofile.htm
This site is reasonably accurate at guestimating what you should
expect if you pop your stats into its calculator for either
ADSL1/2/2+:
http://www.coolwebhome.co.uk/calc/calculator.php
If you have an attenuation of 60dB or higher, may the force be with
you. 60dB is typical of a line length of greater than 5.5Km which is
really at the tip of what ADSL will operate at, at all.
I hope that proves useful somehow!
Cheers,
James.
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