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This chapter is from the book

This chapter is from the book

Comparison of Cable Modem Versus DSL: Speed and Cost

When compared to DSL, the cable modem has few advantages and several disadvantages for Internet access. DSL, on the other hand, has many advantages. Unlike ISDN, DSL isn't metered by the minute. Better yet, DSL is truly an always on service, which makes it suitable for a wider range of applications, including interconnecting LANs, Web site hosting, videoconferencing, and connecting branch offices (see Tables 2 and 3).

Table 2 DSL Versus Cable



Cable Modem

Consistent download speed



Consistent upload speed



Immune to degradation from



neighborhood usage



Secure, exclusively dedicated



line with isolated data



Carrier guarantees performance



Table 3 High-Speed Services Compared








128Kbps to 1.544Mbps

Cost per month




(including Internet service)

for moderate usage


depending on speed


Per-minute charges make full-time connections impractical.

Price can vary with mileage, usage, and service level.

Wide spectrum of services; distance limitations; incompatible versions.


In every cable modem network neighborhood, hundreds (perhaps thousands) of households all share a common transmission medium. Download speed could be high if conditions are optimal with absolutely no activity from neighbors. However, typical download speeds in many neighborhoods are no higher than 400Kbps range during real-world usage. Upload speeds are even slower because the cable modem network is optimized in one direction only and, depending on cable provider, is often capped.


As more users pile onto cable modem services, performance goes down rapidly, diminishing the value of the service. In response, many cable modem providers around the country now cap subscriber outbound speeds at 128Kbps (equivalent to about two 56K modems). DSL is immune from both real and artificial speed restrictions. The quality and value of DSL remains constant for the lifetime of the service, while cable modem Internet quality degrades and loses value over time. Combine that with a yearly term requirement imposed by the cable modem enterprise with each subscription, and you may discover that you are locked into a losing investment.


Aside from performance variations and diminished quality, the shared cable modem network also introduces concern for security. Data from one household passes over the same wire connecting others, potentially exposing credit card, email, and other sensitive data. For this reason, users either find cable Internet access unacceptable or must arrange encrypted software tunneling to secure networks, which impedes performance.

No Surprise Here

Not surprisingly, DSL use is expected to boom. According to market research analysts at TeleChoice 26, the number of installed DSL lines is expected to grow from 566,000 in 2000 to 2,126,000 in 2002, to 4.57 million by 2004. DSL is expected to do well among people working at home (telecommuters) and in urban areas where cable services are not widely deployed.

Residential Users

Residential cable modem service can be a good value for high-speed access. Still, there are some limitations for residential cable modem service, as mentioned earlier. Cable is a shared medium, unlike DSL, which offers a dedicated line for each user. When too many users in one neighborhood try to share the same cable, performance suffers dramatically as users compete for the limited resources that one cable can afford. For this reason, residential cable customers are basically prohibited from telecommuting, hosting Web sites, and using video teleconferencing and any other bandwidth-intensive applications. The security problems of using a shared medium makes cable modem users much more vulnerable to data interception, unauthorized monitoring, and hacking from other users along the same cable network. While there is a market for residential cable modem service, obviously there can be some significant drawbacks.


Telecommuters using cable modem service are required to pay a rate that is generally designed for the few enterprises that have cable modem service available. Service packages start at almost double what a DSL telecommuter would pay for the same speeds. Additionally, cable telecommuters are subject to the same security and bandwidth problems that residential cable customers face. Therefore, cable modem service is not a particularly attractive option for these customers.


Although the number of enterprises supplying DSL service and Internet access is increasing, would-be users face a confusing range of choices about availability, price, equipment, and configuration. DSL service is hardly ubiquitous. Even in areas where DSL has been deployed, if you're too far from the phone enterprise's central office (where the switching hardware is located), you can't get it or you don't get the maximum possible speed. Prices, while reasonable for enterprises, are steep for individuals. 128Kbps service can cost as little as $89 per month, while 1–1.544Mbps service can go for several hundred dollars. Equipment is not widely standardized, and there are a number of DSL variants to contend with (see Table 1).

So, what are the planning implications for the enterprise network manager? Let's take a look.

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