[xDSL Article from Data Communications mag, 3/97]
xDSL Supercharges Copper
DSL schemes promise multimegabit rates over local phone lines - and carriers and vendors are nearly ready to deliver
A nice 4 1/3 page article on xDSL technology appeared in the March, 1997 issue of Data Communications magazine. It was written by Robyn Aber of 3Com Corp. Robyn Aber is the director of WAN business development at 3Com.
It described the history of xDSL, the differing types of xDSL (ADSL, VDSL, RADSL, etc), and also the CAP v. DMT issue.
It was enjoyable reading at lunch time today.
In general, it was very positive about ADSL technology. After quoting the data rates (always impressive!), the article goes on:
"ADSL delivers a couple of other key benifits. First, ADSL equipment being installed at carriers' central offices offloads overburdened voice switches by moving data traffic off the public switched telephone network - a critical problem resulting from the huge amounts of Internet traffic tying up voice networks. Second, the power for ADSL is sent by carrier over the copper wire; as with conventional phone service, the line works even when local power fails. That's and advantage over ISDN, which requires a local power supply, and thus a separate phone line for comparable service guarantees. Third, and another benefit over ISDN, ADSL furnishes three information channels - two for data and one for voice. Thus data performance is not hampered by voice calls."
And later:
"The rollout of ADSL services will begin this year (a few services have already been deployed), and widespread availability will likely occur during 1998 and 1999."
But the caveats come later in the piece:
"A number of critical issues must be resolved before DSL technologies acheive widespread commercial depolyment. For starters, standards are still under development During 1996, both ANSI and ETSI split on the choice between carrierless amplitude phase modulation (CAP) and discrete multitone (DMT) modulation for ADSL" (note: in a sidebar to the article, Aber says "But CAP is not sanctioned as an ANSI or ETSI standard. Further, it offers relatively low ADSL performance and is susceptible to interference because of its use of a singel chanel." I'm confused!)
More concerns mentioned:
"Some of the other outstanding issues are interoperability, security, eliminating interference with ham radio signals, and lowering power system requirements from the present 8 to 12 watts down to 2 or 3."
No specific ADSL vendors are mentioned, but Bell Atlantic, Bellsouth Corp., GTE Corp., Pacific Bell, and US West, Inc. are mentioned as conducting trials in the U.S.
The article cites ISP Interaccess, Co. and ATU Telecom as current providers of ADSL services.
Back to work; I hope this was useful information.
Steve |
