ADSL (G-Lite) for dummies - AWRE,PAIR,ORCT,ASND,COMS,NN Message Board

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Technology Stocks : ADSL (G-Lite) for dummies - AWRE,PAIR,ORCT,ASND,COMS,NN

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To: Jon K. who wrote (180)	5/17/1999 8:38:00 AM
From: John Stichnoth	Read Replies (1) of 201

My understanding is that all the DSL lines get aggregated into a unit called a DSL Access Multiplexer (DSLAM) at the central telephone office. From there one pipe provides access to a more central connection to the multi-gigabit capacities of the internet backbone. The issue of course is that the DSLAMS cost money (duhh!<g>). The telcos and isp's have an incentive to minimize the capacity of their DSLAM and the pipe they provide to the internet. So, a bunch of different 8 meg lines running into the central office can put quite a strain on that pipe. Minimizing the infrastructure support for their higher-bandwidth access is usually ok, because people tend not to use too much of their available bandwidth. For instance, if you download a movie, you'll then start watching it--and won't use your copper line at all for a while. The telcos develop probability models to predict what kind of pipe they need to support their installed access dsl's and analog modems. That usually works just fine, as long as they don't get too cheap about things. On the "Last Mile" thread there has been quite a bit of discussion about quality of service issues. One of the big determiners of QoS, I understand, is the infrastructure support behind the connection. How does the isp get your connection through to the backbone? That kind of thing. Cable works differently. With cable, the line you share is the one going from your neighborhood to the office. In the office they have similar constraints to accessing the backbone of the net. But, they have the additional constraint of sharing bandwidth in the last mile. That is usually not an issue today, the web pages we download are so skinny that we use the bandwidth provided in very short bursts. But try this scenario: George Lucas releases Star Wars 6, "Skywalker's Grandma", for download over the web. It's a 10 gigabit file. [Numbers completely made up] At optimal speeds it might be downloaded in 20 minutes over a DSL line at 8 megs. But, how many of the big and little kids in your neighborhood will simultaneously try to download the film at midnight on the day of its release? In addition to any router and dslam bottleneck issues, the 20 people simultaneously trying to download the big file will see their download times go to 10 or 20 times the 20 minutes. Got to get the kids off...

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