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Avoiding DSL Hell
A slightly-warped SBC DSL users' guide
This is a work-in-progress, but I wanted to post it as-is for the information it contains.

I have been a mostly-happy SBC DSL user for nearly two years; but with a default Windows installation, virtually-worthless quality-of service (QoS) monitoring software clogs the system and there is no default optimization; I would suspect that the setup that most users wind up with these days may be far less than optimum.   This article lays out some things that I have developed based on my experience in software, hardware, and telephone work.  While SBC-centric, much of the included information will apply to all DSL installations--and other broadband users may find it useful, as well.  There will be links to other articles and information, too--there is no need to reinvent the wheel, after all--but I would like to think that the material presented here will bring it all together in a useful way that goes beyond what I have seen published.

It also must be pointed out that what we are discussing here is mostly the transport aspect of your Internet service, not the content.  In this case, SBC provides the transport and Yahoo! provides the content.

Let's start out with links to some of the material and software upon which this article is to be based:

http://www.tldp.org/HOWTO/DSL-HOWTO/index.html -- Though this HOWTO is Linux-oriented, it still contains quite a bit of useful information for Windows users, especially sections 2 (installation) and 6 (overview), though the instructions given in the HOWTO article vary slightly from those that will be presented here.  My technique for filter installation, for example, which is shown here (adapted from the article diagrams):

    <--------Home/Office-------><------Loop------><--Central Office-->     
                                                                         
     X--Voice--+--[RJ11]------+                                          
                              | (filter)     |                                          
  POTS (phones, |              D                      CO                  
   fax, etc.)  |              a                    -------               
               |              t                    |     |               
     X--Voice--+              a                    |     |               
               |              &                    |  D  |               
               |              V  -----             |  S  |=- Voice Switch
     X--Voice--+              o  | N |   2 wire    |  L  |               
                              i-=| I |=-----------=|  A  |               
                              c  | D |  Local Loop |  M  |=- ISP --> Internet
                              e  -----             |     |               
           -----------        |                    |     |               
 PC  X----=|  Modem  |=-------+                    |     |               
           -----------                             -------               

One filter for all phones reduces signal loss and isolates the house wiring from the digital signal.

It has been said that each additional filter is equivalent to adding 700 feet to the signal line.  In addition, filtering ahead of the house wiring reduces possible signal loss and interference from the phone wiring itself.

RASPPPoE is an implementation of the PPPoE protocol upon which SBC, and most other DSL communications, are based.  It has several advantages over the implementation provided by SBC--for example, the DSL connection is treated as if it were a dial-up connection instead of a separate program, such as the provided Enternet package.  PPP is the Point-to-Point Protocol; in order to transfer it over Ethernet, each PPP data packet is "wrapped" so as to make it appear as an Ethernet packet to the network interface in the subscriber's PC.  At the receiving end, the wrapper is stripped and the PPP packet is decoded.  This has an effect on computational overhead and certain settings.  Since some of these settings vary from the defaults, some tweaking may be needed.

The most important of the default settings that should be tweaked is the maximum transfer unit (MTU).  This Microsoft Knowledge Base article discusses MTU settings in Windows XP.  Also see http://www.DSLReports.com -- this site provides both the tests and the tools for the required tweaking.  The TweakTest provides the current values and DrTCP is the tool to get you to the optimized values.

Last revised: 07-June-2004.  Copyright © 2004 Michael Rudas. All rights reserved. The opinions expressed in this article are not necessarily those of the other members of the Oak Park Computer Club. All trademarks and brand names referred to herein are the property of their respective owners. This article was created using the EditPad Classic text editor and Mozilla Composer HTML editor, both free. Permission is hereby granted to publish this article in an unmodified form, except for formatting (contact me for changes or updated versions). Technical questions and help requests can be directed to my tech-support mailbox, the link to which can be found on this site or the OPCC site.