This is part of The Pile, a partial archive of some open source mailing lists and newsgroups.
Subject: Re: DSL shared/non-shared From: "Thomas J. Ackermann (TJACK)" <tj@tjack.com> Date: Tue, 11 Apr 2000 14:21:51 -0700 Hi, At 09:53 AM 4/11/00, Chris Maresca <ckm@crust.net> wrote: >[...] > >DSL lines are not like cable modems (which are like large party lines). >Each subscriber is isolated from the other, effectively a dedicated line, >even if you are on the same subnet as others... The only real problem >with DSL as far as security goes is that some of the modems/bridges are >configurable via telnet and the DSL providers sometimes (often) leave the >default passwords... That is not necessarily true, and varies from provider to provider. Business DSL (usually SDSL to make sense) is more often connected directly connected, and not shared. Some providers (such as Rhythms Business SDSL, which I use at my house) deliver their DSL even via extra cable (not piggy-backed on existing phone line; result: better quality, more bandwidth), and monitor their equipment remotely for failures. PacBell's ADSL (especially to the home user) is shared, contrary to popular belief, for the last mile between the home and the Central Office. There it gets an ATM back-end connection (an approach which allows PacBell to utilize their heavy ATM investment). The same is true for Covad, where they use PacBell facilities (which to my knowledge is the case for the majority of the connections). In that regard, there is no difference for the home user between cable and ADSL. Just my $0.02 ;-)) Thomas === Subject: Re: DSL shared/non-shared From: Chris Maresca <ckm@crust.net> Date: Tue, 11 Apr 2000 15:36:17 -0700 (PDT) This is actually totally wrong. In all cases, DSL is point-to-point. It uses ATM as the transport from the modem to the CO agregation point, which functions much like a switch. These units are made by companies like Redback and Copper Mountain, and are generally connected directly to backbone providers. It is sometimes run over existing phone lines, but is still point-to-point using splitters at each end. In fact, all phone lines are point-to-point, since this is how the phone system is architected, at least from your house to the CO. In the case of Covad, PacBell only provides dead copper wiring, and nothing else. Covad provides all IP infrastructure, including the ATM switch and the DSL/ATM bridge. In contrast, cable modems are more like traditional Thin Ethernet, where each modem is 'tapped' into a trunk line with no switching, sharing the aggregate bandwidth. The trunk line is then terminated at a headend which splits the video and data signals, routing data to an internet backbone. Some cable modem providers will use a protocol called PPPoE (PPP over Ethernet), which tunnels a PPP connection from the local machine to the headend. This, however, does nothing to aleviate the bandwidth problems that cable modems suffer. The only way to handle this is to reduce the number of people on the trunk line, which is expensive. Some cable mode companies have therefore resorted to asymetric bandwidth caps on their users. More information about DSL at: http://www.dslreports.com/ Specifically: http://www.dslreports.com/information/kb/DSL-1/pictures and http://www.dslreports.com/faq/1/12 === Subject: Re: DSL shared/non-shared From: Chris Maresca <ckm@crust.net> Date: Tue, 11 Apr 2000 18:33:28 -0700 (PDT) Everything you state above seems correct, with the exception that the ONLY WAY > cable modem providers eliminate the low sharing of aggregate is to reduce the > number of people. > > Our Florida provider ADDED NEW T(n) lines to increase the bandwidth. True, they can add capacity at the headend, but that does not help the overall 10bt bandwidth at the trunk level, which much be shared. That's where the bottleneck exists. > However, your statements about everyone sharing the same Trunk are correct, > and, worse yet, everyone is as visible as on a large (corp) network.. Not if they use PPPoE or the newer encryption built into cable modems. Otherwise, yes, you can sniff all packets, much like a typical hub-based network... ===