Speeds in practice - DSLzoneUK speed test results as a % of reported modem sync speed, plotted against time of day for four ISPs in the second half of August 2006 :-

With apologies for the pink background - no idea what happened there !

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.

Make	Model	Chipset	MaxDownRate	SNR tweak	DMT	SNMP
BT Voyager	205	Globespan	Yes	No	No	pass
Speedtouch	5x6 family	Broadcom	No	Yes	Yes	pass
Netgear	DG834(G)	TI AR7	No	No	No	pass
Belkin	7633	Broadcom	No	Yes	No	pass
Belkin	7632v1000	Conexant	Yes	No	No	pass
USR	9105	Broadcom	No ?	Yes	No	Yes
Draytek	2800	??	Yes	No	No	Yes
Westell	6100	TI AR7	No ?	Yes	No	Yes
Dlink	DSL-300T	TI AR7	Yes	No	No	Yes
Westell	6301	Broadcom	No ?	Yes	No	Yes

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.