Important ADSL Parameter

SNR Margin

SNR Margin is the difference between actual SNR on the line and the SNR needed for a particular sync-rate or bandwidth. For example, if the actual SNR is 45 dB and the SNR needed to maintain sync-rate at 2 Mbps is 20 dB. Then the SNR margin is 25 dB.

Consistent SNR Margin is essential to absorb fluctuations in interference on the line, and is therefore meant to keep the service stable. SNR Margin is applicable to both upstream and downstream.

Rule of thumb 1:

SNR Margin

Remarks


6 db or below

Poor and subscriber wont be able to sync, intermittent sync problems or any connectivity issue.


7 dB – 10 dB

Fair but does not leave much room for variances in copper line conditions.


11 dB – 20 dB

Good with little or no sync problems


20 dB – 28 dB

Excellent


29 dB or above

Outstanding


Increasing sync-rate by 1 Mbps will reduce SNR margin by approximately 5 dB.

Rule of thumb 2 :

There are two ways to increase SNR Margin:

It is recommended to isolate and remove external source of noise or interference.

· Parallel lines can considerably reduce noise margin and also introduce impulse noise when phone rings or during calls.

· Power lines causing inductive interference especially inside the premise.

· Poor quality drop wire or internal wiring. (Normally can be inspected by the quality of the insulator).

· Poor quality cable pair.

· Improper patching at MDF, Cabinet or DP.

Short-term fix can be done by reducing ADSL sync-rate until SNR level reaches acceptable value.

SNR Margin value can be obtained from modem, ADSL test gear, EMS and BMS.



Attenuation

Attenuation is the amount of transmits power loss due to line impedance and is generally proportional to the length of cable. The maximum operational limit to initiate and maintain synchronization is 65 dB.

under mixed gauge cable environment, usually 13.6 dB loss per kilometer is used to estimate distance.



Rule of thumb:

The attenuation value can be obtained from modem, ADSL test gear, EMS and BMS.



TM guideline for SNR Margin & attenuation:

ADSL Speed

SNR Margin

(Upstream & Downstream)

Attenuation (Downstream)


512 kbps

> 12 dB

< 60 dB


1 Mbps

> 12 dB

< 55 dB

1.5 Mbps

> 13 dB

< 48 dB


2 Mbps

> 15 dB

< 40 dB


4 Mbps

> 15 dB

< 30 dB

Throughput

Throughput is the amount of data moved successfully from one place (e.g., your computer) to another (e.g., any given website on the Internet) in a given time period.

A throughput test is done by downloading and/or uploading a file (depending on the measurement type selected). Download throughput is calculated by taking the file size downloaded and dividing by the time taken to download. Upload throughput is calculated by taking the file size uploaded and divided by the time taken to upload.

Throughput can be obtained from TM Net Speedometer or http://www.izzi.com.my/speedtest.