Rim Semiconductor Company (fka RSMI)

[theforce3]

DSL On The Rise

http://www.techweb.com/wire/story/TWB20010406S0013

we could save them money and bank at the same time.


(04/06/01, 4:59 p.m. ET) By Darrin Woods, Network Computing
DSL swept across the residential broadband Web access market like a tidal wave, and now, after almost two years, the groundswell is finally reaching corporate customers.

While most broadband technologies start in the enterprise market, DSL is different.

The technology was once seen as simply an inexpensive route to high-speed Internet access: For less than $100 a month, homes and small businesses could connect to the public network at speeds approaching DS-1 levels.

Now DSL has grown to include voice and VPN services.

For companies paying more than $2,000 per month for a full DS-1 link to the Internet, DSL is a windfall, and enterprise customers of all sizes are weighing the pros and cons of using the technology to link remote and branch offices.

How did DSL evolve? Its development is written in the annals of security monitoring systems.

Monitoring companies needed instant communication with the alarms in buildings being guarded. Using regular telephone lines was an option, but the RBOCs (regional Bell operating companies) didn't like the idea of keeping a circuit nailed up 24x7 while being able to bill only $20 per month for it.

A solution was to use dry copper pairs that did not pass through the switched telephone network. Circuits didn't need to be nailed up, and most areas had enough spare copper pairs to accommodate the needs of the security companies.

By the mid-1990s, analog modem technology had peaked. Because telephone circuits are digital at their core, there was no way to go beyond DS-0's 56-Kbps to 64-Kbps data rate.

Enter those copper pairs used for security systems. The dry copper lines used for monitoring weren't connected to the PSTN (public switched telephone network), so they could be pushed to very high speeds. Thanks to low tariffs, these lines were also very inexpensive.

Manufacturers began creating devices that would use these inexpensive copper pairs to push data at nearly DS-1 speeds for a mere fraction of the cost of a DS-1 line, and DSL was born.

As with analog connections, devices are necessary at both ends to make DSL work. DSLAMs (DSL access multiplexers) are placed at the CO (central office) to terminate the service provider's end of the connection.

Because the DSLAM is located at the CO, all the DSL lines coming into that location can be multiplexed onto an ATM OC-3 (or higher) link that goes to the service provider's network.

And since most DSLAMs are modular, they can accommodate interface modules for every flavor of DSL supported by the manufacturer.

DSLAMs incorporate ATM or IP as their transmission method of choice, but ATM has until recently been the popular format because of its QoS (Quality of Service) abilities.