Broadband for business: DSL or cable?

By Kevin Railsback, InfoWorld |  Networking

In the not so distant past, accessing the Internet from work was an activity reserved only for those employees who had a pressing business need to do so. In many cases, these lucky few even accessed the Web via individual modem lines. Of course, the Internet has since invaded every facet of the corporate world, and now companies are looking for economical ways to provide comprehensive Web access not only to all on-site employees but also to remote workers and home office networks.

Because simple dial-up accounts are too expensive for large groups of disparate users, most companies use either DSL or cable modems for cheap broadband access. Which solution is best for your company? This very question ignites a fiery and informative debate between two of our Test Center analysts.

Underlying Technology

Todd: Cable modem technology, which leverages existing coaxial cable wiring in a home or business to transmit digital data, is largely based on Ethernet-technology developed at Xerox Parc in the 1970s. Unlike xDSL, the connection between a cable modem and an ISP is not an individual line -- it is a shared connection among all users assigned to the same network node. Each cable modem talks to a Cable Modem Termination System (CMTS), which brokers all data requests. The best analogy for this setup is a large-scale client/server model with two-way communication between cable modems (clients) and a CMTS (server).

Because each node resembles nothing more than a large LAN, cable providers are able to use off-the-shelf hardware components and communicate with heterogeneous clients -- such as Windows, Mac OS, and Linux -- using standard TCP/IP protocols. Not only does this result in lower costs, which benefits consumers, but it also means that cable ISPs avoid having to write network drivers for every operating system.

To realize just how crucial a benefit this is, try talking to an xDSL subscriber who is struggling to use his or her service after upgrading to Microsoft's new Windows Me operating system.

Kevin: While cable works on a shared-network type topology, xDSL is designed around other existing WAN topologies. Basically, ADSL or SDSL (Asymmetric DSL or Symmetric DSL) is designed to work like T1 or T3-type technologies. The DSL modem at the customer site connects the local Ethernet network (be it a router or a switch or a direct connection to a PC) to the back end ATM network. This gives access to the ISP's network, which is providing the actual Internet access.

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