Thursday, August 24, 2006

Routers....

the challenges of MaxDSL and longer lines are handled with varying degrees of success by different models of ADSL router. This is an attempt to identify routers with pertinent features. Some folks have found that modems from the same chipset as the exchange DSLAM work best, so I'll try to include that as well. The abbreviations used for Vendor ID are a bit confusing at times.

The features identified include :-

MaxDownRate - the ability to limit downstream modem sync speed. This gives a higher SNR margin and hence more reliability, or the capacity to accept a night-time noise increase without a resync.

SNR Margin tweaks - commands that allow the user to adjust the target SNR margin so that the modem syncs at a lower speed (higher margin) or higher speed (lower margin) than it would if left to its own (and the exchange's) standard settings.

DMT - compatibility with the German DMT software tool which provides a GUI access to router configuration and tweaking commands plud monitoring information.

SNMP - SNMP functions to allow graphing of throughput, sync speed, SNR margin etc using tools like PRTG.

MakeModelChipsetMaxDownRateSNR tweakDMTSNMP
BT Voyager205GlobespanYesNoNopass
Speedtouch5x6 familyBroadcomNoYesYespass
NetgearDG834(G)TI AR7NoNoNopass
Belkin7633BroadcomNoYesNopass
Belkin7632v1000ConexantYesNoNopass
USR9105BroadcomNo ?YesNoYes
Draytek2800??YesNoNoYes
Westell6100TI AR7No ?YesNoYes
DlinkDSL-300TTI AR7YesNoNoYes
Westell6301BroadcomNo ?YesNoYes

Note that some features may be available in individual versions of firmware and not in other versions, or may be confined to certain versions or batches of the stated model. It is common for manufacturers to maintain a model number through a range of alternative hardware & firmware configurations and the user may not be able to check this before purchasing.


The TI AR7 chipset has a good reputation on long lines, especially if combined with a TI DSLAM. MaxDownRate limits are helpful to sure instability, and SNR tweaks to get more speed out of a line with a high target SNR margin. SNR tweaking can also reduce speed and increase margin, when I tested a USR9105 it appeared to only tweak the margin up and the speed down.


When using these "semi supported" features like maximum down rate or SNR tweaking you may find the setting disappears on a reboot. An automated telnet program can be used to quicky restore favourite settings.

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