How does DSL compare to Cable Modem Internet Access?
No discussion of DSL technologies would be complete without a review of cable modems. These modems use cable TV companies’ coaxial networks as the transport medium. DSL technologies use the Regional Bell Operating Companies’ (RBOC) telephone network to transfer users’ data.
There are several major issues that impact the deployment and use of cable modems. The first is that a limited number of existing coaxial distribution systems are capable of two-way traffic. The cable industry is investing heavily to upgrade their facilities to a hybrid fiber /coax based network. Most coaxial networks are designed for one-way downstream distribution only, requiring the expensive replacement of distribution nodes. The second is that all subscribers on a distribution network (from 500 to several thousand homes) share the bandwidth, which can reduce an individual’s throughput to analog modem dial-up speeds.
Most cable providers advertises their Internet access speeds to be up to several MB/second. This is simply not the case and is largely a marketing gimic to attract new customers. Under ideal laboratory conditions, the speeds they advertise might be possible. However, in the real world your bandwidth usage will be dramatically decreased by may factors including other users in your neighborhood. The fact also remains that few sites on the Internet can deliver data to you very fast anyway. Most sites only deliver data at 1MB/sec or slower. If you truly had a 3MB/sec cable connection, you would never take advantage of the full speed if you can only receive data from the SENDER at 1MB/sec or less. Large pipelines that are 2MB/sec or faster usually only help if you have many users in your office sharing the same connection.
For users who SEND or UPLOAD a lot of data such as e-mail attachments, Cable will be a poor choice since the upload speed is always much slower than the download speed. Typically, cable upload speeds are only 256K compared to DSL which can be as fast as 1MB/sec. Cable companies always forget to mention this, but it can be a very serious problem if you plan sending much data at all.
Most importantly from a speed perspective, DSL puts the potential bottlenecks in areas that your Internet provider can control. For instance, if the ISP’s connection to the Internet is filled with client’s data, they are in control of that. They can upgrade their pipelines and fix any bottlenecks.
With cable, if a neighborhood is saturated with very heavy use, there is very little that the cable company can do to increase the available bandwidth to you. It’s a “best effort” network and when it’s full, everyone will suffer.
Another cable modem topic of discussion is that un-terminated cable TV jacks, (no TV connected and no terminating resistor cap screwed on), act as antennas on the distribution node. Any RFI-generating (radio frequency interference) equipment near an un-terminated jack injects noise into the entire distribution network. AC motors (vacuum cleaners), computer monitors, fluorescent lights, and a host of other household items generate RFI. This is not critical for TV viewing, but can adversely affect modem throughput.
Since DSL runs over your telephone line, you may have your high-speed connection anywhere in your home or office. Cable service will only be available where your television jacks are located, which may be less convenient.
Another significant factor when using Cable is the fact that you are stuck with only one service provider that can give you service. If you are unhappy with their service, there is no way to change providers.
With DSL, you often can choose from several dozen or more ISP’s who can do your Internet access, e-mail and other services.
Lastly, since cable is a shared network in your neighborhood, there are serious security issues that need to be addressed. Many cable modems are now set up as firewalls, but they need to be configured and maintained otherwise all other users in your neighborhood can “see” your network.
