DSL is next hot comm service
DSL is next hot comm service
Companies see it as best way to deliver broadband links to LANs, WANs
By William Jackson
Digital subscriber lines in various flavors have emerged as the top choice for delivering broadband network connections over the last mile'or the last five miles or so'of the existing telecommunications infrastructure.
DSL products, from chip sets to mechanical cross-connect switches, were practically everywhere on the exhibit floor at the recent SuperComm '99 trade show in Atlanta. More than 30 companies displayed products and services based on the proposed G.lite asynchronous DSL standard alone. Some of the products and services boosted speed, some increased capacity and some extended the range of DSL services.
The 10 biggest competitive local exchange carriers are rushing to provision' for DSL, said Peter Benisti, vice president of sales for NHC Communications Inc. of Quebec, maker of the Switchex/DVS cross-connect switch. Carriers use the switch to test their local loops, he said.
Oren Teper, a technical support engineer for Orckit Communications Ltd. of Tel Aviv, Israel, said GTE Corp. has equipped more than 470 of its central offices with DSL equipment from his company.
Businesses are going to have a very happy time [with DSL] this year,' said Paul Nurflus, product manager for Metalink Transmission Services Ltd. of Tel Aviv. 'Residential is going to come later.'
DSL technologies carry digital signals over the copper local loops of the switched telephone system. Asymmetric DSL, which is faster downstream than upstream, can share a voice telephone channel. Symmetric DSL has the same speed in both directions but generally cannot accommodate a voice channel.
Microsoft Corp. president Steve Ballmer, speaking at SuperComm, said more user bandwidth is crucial to advanced networking. 'Broadband is essential,' he said.''
Although Microsoft has no bias for broadband access via DSL, cable or wireless connections, its future Windows operating systems will be optimized for DSL. Ballmer said the company is teaming with switch manufacturers to use DSL access.Only one platform
Metalink's Nurflus said the company wants to make a single silicon platform for symmetric and asymmetric DSL.
Nurflus said a single platform would be more affordable and would simplify networking.
The company has announced a multimode chip set for DSL access multiplexers and routers that can handle software configurations for single-line DSL (SDSL) and high-bit-rate DSL (HDSL), both of which use two copper pairs, as well as SDSL2 and HDSL2, which use a single copper pair.
Future chip set releases will incorporate ADSL and G.lite ADSL, too. 'That's a major challenge,' Nurflus said.
Just how much bandwidth users will get out of DSL will depend largely on their distance from a central telephone office. Generally, the greater the distance, the slower the transmission speed. ADSL can deliver 64 Kbps to 800 Kbps upstream and 500 Kbps to 8 Mbps upstream over a single wiring pair at distances of 12,000 feet to 18,000 feet. Different flavors of SDSL range from 26 Mbps to 144 Kbps.
Adtran Inc. of Huntsville, Ala., announced H2R, an HDSL2 repeater that effectively doubles the 12,000-foot service range. Without a repeater, the symmetrical service, which can provide T1 speeds over a single copper pair, could reach only about 60 percent of telephone users, said Keith Atwell, Adtran's product line manager. With the repeater, HDSL2 could serve as many as 95 percent, he said.
A second Adtran product, Total Reach SDSL, extends SDSL without a repeater.
DSL has been around for several years in the T1 market, but adoption of the always-on ADSL with a concurrent phone channel has been waiting for central-office equipment that can work over local loops. Although ADSL is seen as vanquishing Integrated Services Digital Network for broadband residential access, competitive local exchange carriers will first market ADSL to businesses, Nurflus said.