 almost exclusively residential service providers; if they are to break into the potentially lucrative busi- ness market, they must have a presence there. Cable Modems As cable providers have progressively upgraded their networks to include more fiber in the backbone, their plan to offer two-way access to the Internet has become a reality. Cable modems offer access speeds of up to 10 Mbps, and SO far the market uptake has been spectacular. Cable modems provide an affordable option to achieve high-speed access to the Web, with current monthly subscription rates in the neigh- borhood of $40. They offer asymmetric access, that is, a much higher downstream speed than upstream, but for the majority of users this does not represent a problem, since the bulk of their use will be for Web surf- ing-during which the bulk of the traffic travels in the downstream direction anyway. While cable modems do speed up access to the Web and other online services by several orders of magnitude, there are a number of downsides that must be considered. The greatest concern that has been voiced about cable modems is security. Because cable modems are "always on," they represent an easy entry point for hackers looking to break into machines. It is, therefore, critical that cable subscribers use some form of firewall software or a router that has the ability to perform filtering. Data over Cable Standards As interest grew in the late 1990s for broadband access to data services over cable television networks, CableLabs®, working closely with the ITU and major hardware vendors, crafted a standard known as the Data Over Cable Service Interface Specification, or DOCSIS®. The standard is designed to ensure interoperability among cable modems as well as to assuage concerns about data security over shared cable systems, DOC- SIS has done a great deal to resolve marketplace issues. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use 