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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here
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To: Frank A. Coluccio who wrote (286)10/2/1996 10:05:00 PM
From: Tom Eames   of 12823
 
Frank

You obviously know some of the dirty little secrets of telephone lines! Yes sealing current is crucial to keeping splices from oxidizing and going bad. For regular two wire telephones its your battery, off hook and ringing that serves that magical pupose. Your point about for four wire circuits ( DDS, T1 etc..) is correct and that is why they experience low splice problems. For ISDN ( a two wire service without DC) the trick that is specified by Bellcore is to occasionally apply a gradually rising voltage then falling voltage across the two wire line to punch the oxides every few seconds or so. This is almost DC and doesn't bother the ISDN signal. xDSL needs a similar design or it won't work for long with splices especially in the humid south. There are no crossconection count rules but there are length and bridge tap rules ( a bridge tap implies a splice ). The equalizers and FEC in the xDSL modem receivers are designed to deal with the reflections from the splices and bridge tap ends as well as the ingress from radio and other EMI sources. The bottom line is that a significant number of existing lines will just work and the ones that don't will either get the splices cleaned up, bridge taps removed or the length shortened by going out to a CEV or cabinet closer to the customer. As long as the number of loops that require this cleanup is say under 10% or so then the labor cost will not be prohibitive. That was the strategy for ISDN (93%) and I think xDSL will follow a similar model. Remember also that ADSL is a lttle more troublesome than VDSL since VDSL is expected to be shorter with fewer splices and taps and larger gauge wire besides offering higher rates. I would like to say that the ANSI T1E1 and ETSI TM3 standards groups, the members and Bellcore have researched these issues at length and the results look promising. Only real live deployment will tell but I believe it will work for what thats worth.

Tom
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