Expected speed based on 'resistance' reading?

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ashtonaut

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#9676 4-Oct-2006 10:22

Hi,

After calling TelstraClear yesterday and finding out our suburb (Avonhead, Christchurch) doesn't have access to TCLs cable internet, I called Telecom to find out about Jetstream availability.

The guy checked our number and confirmed that Jetstream appeared to be available, but there was no guarantee until everything was connected up (fair enough).

I have read that the distance from the local exchange is one important factor in determining how fast the connection will be. So, I asked the guy where the nearest exchange was:

Me: "So, can you tell me how far away the local exchange is?"
Him: "No, sorry, I can't"
Me: "Why? Does Telecom not have this information?"
Him: "Yes, we do have this information, but it is private and we can't tell customers"

I was amazed - does anyone have any idea why Telecom don't tell customers how far they are from their local exchange? I can't think of any good reason why this information isn't public...

All he would tell me is that the "resistance" reading on our line was "22" (he didn't mention units). He said this value meant I was "pretty close" to the exchange.

Can anyone tell me what this "22" is actually a measure of, and how it compares with most connections? Based on this number, would I expect to get a decent speed out of a Jetstream connection? (I know there are several other factors that influence final speed, but let's just assume all other things remain equal here).

Cheers,

Ash

JAMMAN2110

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#47497 4-Oct-2006 11:26

Perhaps they can't tell you because they don't know themselves..

Although one would assume that if it was "resistance" it would be Ohms...

Fraktul

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#47515 4-Oct-2006 13:26

Telecom measure resistance in monkeys per foot second. At 22 monkeys per foot second, resistance is futile.

cyril7

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#47516 4-Oct-2006 13:45

Telecom measure resistance in monkeys per foot second. At 22 monkeys per foot second, resistance is futile.

LOL.

I think the main reason they wont tell you where the exchanges are is because they are concidered an important infrastructure detail, and as such can become the target of terrorism. And we dont want Billy boy to have to come down here and stamp it out now do we.

Cyril

juha

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#47555 4-Oct-2006 18:34

Line attenuation, measured in dBm, possibly.

Juha

3g

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#47559 4-Oct-2006 18:54

I know that Telecom can give you quite a bit of information based on the response I received from them a month or two ago:

"For your information you are 137m from the Broadband equipment with resistance of 37 Ohms and line noise of 3dB."

Distance sounds good - not sure about the other figures.

Nigel H.

SilentOne

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#47585 4-Oct-2006 21:31

You can ring and ask for this information.. distance, ohms & Db.. however they won't always tell you exactly where an exchange is (ie street adress).... just ring up and ask them for a broadband line check so you are able to find out how far away it is.. at the same time they will be able to ascertain the noise in Db and the resistance in Ohms.

The information from memory takes about and hour to get and reply back so if you call they should be able to email it or ring you back.

They don't hold back this information..... you are allowed to ask for it.... the Telecom Rep may not be aware your entitled to ask but they don't intentionally withold it.

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juha

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#47589 4-Oct-2006 21:39

No, it's not withheld information at all, which is a good thing.

Juha

ashtonaut

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#47613 5-Oct-2006 08:54

Thanks for the replies. I called back, got put through to Technical Support, who then forwarded the request to Advanced Technical Support. I got a call back fifteen minutes later telling me that the distance to the exchange was just over 1km, and the "noise resistance" (hmmm) was 21dB (I take this to be the resistance value).

So - back to my original question - how does a resistance of 21dB compare to others? The lady on the phone said the results were 'very good', would others agree?

cyril7

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#47614 5-Oct-2006 09:06

Makes more sense, they will be refereing to the Downstream attenuation, which a figure of 22dB is good.

At just over 3.5km from the DSLAM my Belkin modem reports 48dB and I get a connection speed of 4.2Mb/s. The uplink attenuation is 28dB and connection speed of 160kb/s.

So at 22dB I assume you should be able to acheive nearly full rate or at least 7Mb/s or greater.

Cyril

ashtonaut

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#47615 5-Oct-2006 09:07

Great, thanks Cyril :)

JonC

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#47651 5-Oct-2006 13:33

This is veering slightly off-topic, but I have a TCL cable modem and it reports a signal-to-noise ratio of 39dB. This is obviously a completely different case as it's a TCL cable modem reporting SNR rather than an ADSL modem on phone line reporting attenuation, but for a signal-to-noise ratio, presumably the higher the dB, the better?

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cyril7

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#47654 5-Oct-2006 13:47

JonC your are correct the Signal to Noise ratio is just that a ratio in dB, therefore the more the better, every 3dB indicates a doubling of power ratio. Ie if your 39dB S/N increased to 42dB but the carrier power remained the same then it would indicated that the noise power had reduced to half what it was.

ADSL modems also deal with C/N (or Signal to Noise) but the attenuation fiqure is just a simple method for quickly evaluating the lines length and potential ability. It obvously does not indicate if there was a strong interference on the line.

My modem as I previously stated indicated 28dB line attenuation, it also indicated 17.8dB S/N on the download circuit.

Cyril

barf

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#47662 5-Oct-2006 14:19

Attenuation is to AC circuits (ie phone lines) what resistance is to DC circuits. Thats a heap of textbooks thrown out the window but hopefully helps you understand.

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JonC

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#47664 5-Oct-2006 14:27

Whoah - just had a flashback to 6th-form Physics :-) It's all coming back to me now - thanks barf and cyril.

Fossie

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#48227 10-Oct-2006 17:29

My router gives me this information:

SNR Margin (dB):	14.9	31.0
Attenuation (dB):	25.5	20.5
Output Power (dBm):	11.1	19.8
Attainable Rate (Kbps):	5824	1056
Rate (Kbps):	4288	160

(is the attenuation any good?)
How does this compare to everyone elses?