SNR Margin ??

Forums › New Zealand Broadband › SNR Margin ??

bw

3 posts

Wannabe Geek

#10835 14-Dec-2006 20:16

Hi
Can anyone confirm a decent SNR margin for an ADSL router ?

my current one seems to jump between 6-12 on the down. From what I have googled it seems it should be alot higher 25+ ?

my current download speed tests range from 50 - 1500 k and fingers acrossed its something telecom can fix

thanks

Brendan

Whistleblower

7 posts

Wannabe Geek

#55531 15-Dec-2006 08:03

Hi there,

Your router should be able to give you SNR Margin, Line Attenuation & Physical Connect Rate figures.

First up the Physical Connect Rate is pretty important.

I’ve found not all routers “are equal” in determining what your Physical Connect Rate is.

For example, a DSL-G604T router never achieves a physical connect Rate that gives me a download speed more than 1.2Mb, where-as if I connect a Nokia M1122 router I can get 2.1Mb. How annoying.

So, with Service Providers saying "as fast as your telephone line can give you" is pretty interesting, when different equipment can get more data down my telephone line.

Then, those other numbers (as a guide because Alcatel/Telecom NZ have various approaches to massage these numbers..):

SNR Margin
In general, a higher signal to noise ratio will result in less errors.

6bB. or below = Bad and will experience no line synchronisation or intermittent synchronisation problems.
7dB-10dB. = Fair but does not leave much room for variances in conditions.
11dB-20dB. = Good with little or no synchronisation problems
20dB-28dB. = Excellent
29dB. or above = Outstanding

Attenuation Rates

In gerneral, attenuation is the loss of signal over distance. Unfortunately, dB loss is not just dependent on distance. It also depends on cable type and gauge (which can differ over the length of the cable), the number and location other connection points on the cable.

20bB. and below = Outstanding
20dB-30dB. = Excellent
30dB-40dB. = Very Good
40dB-50dB. = Good
50dB-60dB. = Poor and may experience connectivity issues
60dB. and above = Bad and will experience connectivity issues

Distance

And for distance, the equation I have seen suggests that downstream attenuation divided by 13.81 will roughly equal KM from the exchange. For example; if you had a downstream attenuation of 40dB...

40dB / 13.81 = 2.896 KM

For me, 17 / 13.81 = 1.2KM

If you request an AMFM/ADSL test from Telecom including they advise you if you connect via a "Conkin", they will provide one and update your telephone account notes with the outcome. An AMFM test provides Ohms, distance etc, and if "Conklin" equipment is on your neighbourhood, then this applies to you:
http://www.geekzone.co.nz/forums.asp?ForumId=49&TopicId=10288&page_no=5

Speed

A prickly topic.

If you go to www.jetstreamgames.co.nz/speed and complete the 1Mb download speed test and record the details. Clear your browser cache.

Then, as fast as you can, change the userid/password in your ADSL router to be user@jetstreamgames.co.nz with any password, restart your connection, and repeat the speed test (the only website you can get to with this login is www.jetstreamgames.co.nz/speed )

If you find the second speed test has a DRAMATICALLY increased speed results, then there 'could' be an issue with your ISP ATM link.

If you find the first and second speed test results pretty similar, and the speed is awesome, that's good.

But, if you find the first and second speed test results pretty terrible, then perhaps your ADSL Physical Connect Rate on the telephone line that is responsible, AND/OR the capacity available at your telephone exchange at the time of the tests being run.

Good luck.

Wendy

59 posts

Master Geek

Trusted

#55535 15-Dec-2006 08:51

Speed
A prickly topic.
If you go to www.jetstreamgames.co.nz/speed and complete the 1Mb download speed test and record the details. Clear your browser cache.

Then, as fast as you can, change the userid/password in your ADSL router to be user@jetstreamgames.co.nz with any password, restart your connection, and repeat the speed test (the only website you can get to with this login is www.jetstreamgames.co.nz/speed )

If you find the second speed test has a DRAMATICALLY increased speed results, then there 'could' be an issue with your ISP ATM link.

Just be aware that if you're on UBS using the login user@jetstreamgames.co.nz will not work as your connection is tunnelled directly to your ISP and all that happens is that your ISP sees failed authentication attempts with this username (we see it all the time).

grant_k

3539 posts

Uber Geek
+1 received by user: 124

Trusted

#55539 15-Dec-2006 09:13

Thanks heaps Whistleblower for that very informative post

.

I've seen all those figures reported by my router but didn't have any definite ideas on how to quantify them. Your post provides that and much more.

Now I can quickly assess a connection and make a judgement call as to whether there are likely to be synchronisation problems or not.

Cheers,
Grant.

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#55543 15-Dec-2006 09:44

Excellent post Whistleblower.

Cyril

bw

3 posts

Wannabe Geek

#55601 15-Dec-2006 18:48

thanks for the info

Telecom at this stage agree the snr level shouldn't be going up and down so we will see what happens...

weasel

2 posts

Wannabe Geek

#56430 27-Dec-2006 19:59

Wendy:

Speed
A prickly topic.
If you go to www.jetstreamgames.co.nz/speed and complete the 1Mb download speed test and record the details. Clear your browser cache.

Then, as fast as you can, change the userid/password in your ADSL router to be user@jetstreamgames.co.nz with any password, restart your connection, and repeat the speed test (the only website you can get to with this login is www.jetstreamgames.co.nz/speed )

If you find the second speed test has a DRAMATICALLY increased speed results, then there 'could' be an issue with your ISP ATM link.

Just be aware that if you're on UBS using the login user@jetstreamgames.co.nz will not work as your connection is tunnelled directly to your ISP and all that happens is that your ISP sees failed authentication attempts with this username (we see it all the time).

On that note, if you have issues with customer connectivity where the customer has ADSL sync, but you are unable to see their login requests on your RADIUS or LNS (ignoring the usual VPI/VCI settings etc), then it's possible there's a tunneling fault. A common one we see is where the customer has had their line moved from one DSLAM to another (a port "re-host") and (I think...) their new DSLAM has the port config set to Xtra by default. When this happens, try and get them to log in to the Jetstream Games realm - if they can, they're tunneled to Xtra. In this case, we generally wait until the port configs are generated next (the port configs are generated automatically at 1am, 7am, 1pm, 7pm AFAIK... correct me?) - and if it's still not happy, we go ahead and report a tunneling issue to WS faults.

.. This kinda sucks, because it means Xtra can provision lines faster than UBS in some cases since there is no PVC setup required?

Bah.

Lenovo

Shop now for Lenovo laptops and other devices (affiliate link).

cokemaster

Exited
4937 posts

Uber Geek
+1 received by user: 1089

Retired Mod

Trusted

Lifetime subscriber

#56431 27-Dec-2006 20:06

As far as I know, connections to Xtra still require PVC. I've had issues on family connections where PVC had to be recreated.

webhosting

Loose lips may sink ships - Be smart - Don't post internal/commercially sensitive or confidential information!

Fraktul

836 posts

Ultimate Geek

Trusted

#56436 27-Dec-2006 21:10

The PVC config is still there, what is probably setup be default is that there is an identifier send to the LAC which proxys the PPP setup via a L2TP tunnel to your ISP's LNS. It is this identifier is probably set to Xtra be default.

weasel

2 posts

Wannabe Geek

#56466 28-Dec-2006 10:52

.. This kinda sucks, because it means Xtra can provision lines faster than UBS in some cases since there is no PVC setup required?

Bah.

Oops, should have read 'No PVC config change required' or something like that.. but Fraktul hit the nail on the head anyway :) Cheers!

cokemaster:

As far as I know, connections to Xtra still require PVC. I've had issues on family connections where PVC had to be recreated.

I think some of the good sorts in WS faults tend to blow away (*wink*) and recreate the PVC on the Nokias when it decides not to play ball. Port resets and PVC recreation on the Alcatels seems less common, from what I've gathered... and port resets on Alcatel gear hardly ever works. :(