How to improve SNR ?
Hot tips for reducing line noise
- Make sure the unshielded receiving wire (i.e. wall to modem phone cable) is as small as possible in length.
- Use the first point in the house (generally the one closest to the front of the house). Branch it out after the splitter if required.
- Make sure there’s no devices on the line causing noise (unplug everything else).
- Keep the modem and line away (1m+) from anything else that uses power.
ATM
ADSL is only a physical layer specification, i.e. how the data should be transmitted over the line. ADSL then implements a network layer specification called ATM. ATM is designed as a large switching network run at very high speeds (fibre optic, etc). You find a path through an ATM network via two numbers, a virtual path identifier (VPI) and a virtual circuit identifier (VCI), written as VPI/VCI. Given that ADSL is a point to point network and not large scale switched network it really doesn’t matter but both sides have to be listening at the same address. In Nepal, the traditional ADSL VPI/VCI is 8/81, as a general rule each country or region tends to use its own default values.
NTC ADSL modem configuration: Routing Mode
VPI – 8 VCI – 81
Encapsulation – PPPOE/LLC
Authentication – CHAP
Username – adsl123456(Provided by NT )
Password – adsl123456(Provided by NT)
Change your password after first successful login at http://ntbro.ntc.net.np:8086/
PPPoE vs PPPoA
PPPoE – Point to Point Protocol over Ethernet
PPPoA – Point to Point Protocol over ATM
PPPoE uses one extra eight bytes long header which eats into the payload. PPPoA does not have this header so it has less overhead and each packet can carry more useful data (8 bytes more) which results in slight (around one percent) speed improvement.
Note: NTC ADSL only supports PPPOE
MTU issues
The default MTU for PPPoA is 1500 bytes. The same default for PPPoE is 1492 bytes (8 bytes less due to increased overhead because of one extra 8 bytes header mentioned above/1454 bytes MTU for PPPoE).
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COUNTERS ON DSL STATISTICS. What do they mean?
FEC – Forward Error Correction – packets with errors that have been fixed.
CV or CRC – Code Violation or Cyclic Redundancy Check – packets which have to be retransmitted due to errors.
ECS – Error Corrected Seconds – counter of number of seconds in which a FEC occured.
ES – Errored Seconds – counter of number of seconds in which a CV/CRC occured.
SES – Severely Errored Seconds – counter of number of seconds in which 10 or more CV/CRC occured.
UAS – UnAvailable Seconds – number of seconds that the connection wasn’t able to transmit in.
LOS – Loss of Signal Seconds – number of seconds that DSL singalling has been lost.
