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 TEST CENTER Broadband for business: DSL or cable? By Todd Coopee and Kevin Railsback, Infoworld Test Center November 3, 2000 Two wired Test Center experts argue about the corporate viability of DSL and cable
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. Todd, I'm not sure what you mean when you talk about DSL subscribers who upgrade to Windows Me. A DSL modem gives the user an Ethernet jack to plug in to, just like a cable modem does. There's no difference between the two technologies here at all, except for the cable industry's hype about how DSL is so difficult to set up. Bandwidth issues Kevin: As the cable industry claims in its commercials, cable sometimes offers more bandwidth than DSL for the same cost. But with cable you're sharing a limited amount of bandwidth with others on your segment. With DSL, each user has his or her own dedicated copper that goes directly to the phone company's central office. It is also true that if you want the higher bandwidth offerings of DSL you must pay more. But this is true of every other WAN option, and I don't see what's so weird about the idea of paying more for faster service. Then of course there's upload speed. With DSL there is a choice of both downstream and upstream bandwidth. Downstream is typically a guaranteed 384Kbps with bandwidth up to 1544Kbps available, depending on your line conditions and distance to the phone company's central office. Upstream speed is normally 128Kbps, just like cable. But DSL can be customized to the user's needs, whereas the upload speed of standard cable modem service is capped at 128Kbps. If you need both high downstream and high upstream bandwidth, SDSL allows 384Kbps to 1544Kbps in both directions, or even higher speeds if needed. Todd: Because cable takes a shared bandwidth approach, its performance can fluctuate with the number of users on a particular segment. The larger the number of users, the less bandwidth available for allocation to each individual workstation. Often this can result in performance fluctuations and degradation. Many cable modem providers are working around this problem, however, by placing restrictions on the number of modems per CMTS, and by blocking or filtering certain types of bandwidth-hogging IP traffic. Companies such as Lucent's Bell Labs are also amplifying the fiber-optics used in cable technology to make them operate at increasingly faster speeds, which will also decrease performance bottlenecks. Industry averages for cable speeds usually check in around 750Kbps over a range of 500Kbps to 3Mbps. Kevin is correct that some vendors cap the upload speed to 128Kbps. But many vendors are also easing their cap rates up a few notches. It appears that xDSL has an advantage here. But before all you DSL mavens -- like you, Kevin -- rejoice at my admission, remember that the entire Internet is based on the notion of shared bandwidth. So while the bandwidth of an individual DSL connection may not be shared, eventually all DSL connections will terminate at an Internet router, at which point these individual streams will merge together into one or more upstream connections, causing a potentially hazardous bottleneck. Installation hurts Todd: Let's be honest, Kevin. Installing DSL can be more painful than undergoing gum surgery. I have often read that DSL actually stands for "Damn that Service is Lousy." And what's up with having to use "micro-filters" on all of the telephones in your remote office anyway? DSL installations rely heavily on the quality of phone lines and the distance away from the phone company's central office. If you are more than 18,000 feet away from a central office, you can expect performance and installation problems, period. In comparison, cable offers a painless installation process. In general terms, an existing coaxial cable plugs into the cable modem, and an Ethernet cable runs from the output of the modem to a network hub or network interface card. This simple process requires minimal software configuration on a user's workstation. Kevin: I must admit, typical DSL installations can be pretty bad. As with any other very popular service, it can take weeks to get a DSL line installed. When I had mine installed a year and a half ago, the wait was only four days, but because I was an early adopter, the demands on installation crews were not as intense as they are today. Fortunately, many DSL providers are now offering self-installation kits, and doing it yourself is no more difficult than connecting a few wires and installing a new phone jack. Security issues Kevin: When it comes to security, DSL wins hands down. There are two major issues here: overall network security and VPN capabilities. As far as network security goes, DSL and cable offer similar features. But with DSL, each end-user has a dedicated connection to the central office. With cable, all users share the same cable with others in their neighborhood, which not only endangers privacy, but also diminishes the overall bandwidth for each cable user. As far as VPN capabilities go, DSL and cable should be identical. But some cable providers have clauses in their service agreements prohibiting the use of VPNs across their networks unless you pay a higher cost. This reminds me of the DSL cost structure that cable people complain about in their TV ads. In contrast, DSL providers have no such restriction, and a basic business DSL line, at least in my area, is priced identically to a basic personal DSL line. While it may be difficult for the cable company to detect if you're using a VPN across its network, the very thought of an institution restricting your IP-based services should be a big red flag to any responsible IT department. And besides, do you really want to depend on your local cable company for your business Internet access? I sure don't. Todd: DSL companies point to cable's shared-bandwidth as a glaring, potential security hole, and they have some valid points. Even I was surprised to open up the Network Neighborhood on my local PC and see everyone's PC in My Neighborhood that was attached to the cable network. But some companies such as Cox cable are taking very effective actions to address these security concerns. For example, some ISPs have turned off all of the IP ports that support Windows file sharing and others are allowing customers to call and request that file sharing ports be blocked on an individual basis. In addition, the next generation of cable modems will support the Data Over Cable Service Interface Specification (DOCSIS) 1.1, which provides numerous security hooks and safeguards for data transmission. Parting shots Todd: Honestly Kevin, I have used both cable and ADSL services over the past few years, and I concede that both have their merits. Because competition is a good thing for consumers, let's hope that both technologies flourish and provide us with two reliable and low-cost options. But until xDSL can iron out its installation issues and do something about its distance limitations, cable is clearly the alternative of choice. Kevin: Ack! The last thing I want is for my Internet service provider to start blocking ports and filtering my Internet connection. Besides, Windows file sharing ports are far from being the only vulnerabilities that need protection. For the soccer-mom users out there, or for those who can't yet get DSL in their area, cable modems are a good choice. But I've had too many problems with my cable company in the past to ever trust my Internet access to it. Return to the Test Center's Special Report on Broadband Kevin Railsback, West Coast technical director for the InfoWorld Test Center, believes that until we all have wireless gigabit connections for our toasters and cappuccino machines, DSL will work just fine. Send him your thoughts at kevin_railsback@infoworld.com. Todd Coopee, technology analyst for the InfoWorld Test Center, was on of the first beta-testers of the @Home cable network in West Hartford, Conn. Drop him a line at todd_coppee@infoworld.com. SPONSORED WHITE PAPERS 
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