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On this page:
Introduction
Cable Modem
DSL
Comparing Cable Modem and DSL

Introduction

This page gives general descriptions of, and a table comparing cable modem and DSL (Digital Subscriber Line) service for high-speed connection to the Internet, and to MITnet. For more information, see High-Speed Remote Access to MITnet. In selecting a service provider, always check the provider's web site for detailed, up-to-date information about what is offered, technology requirements, and current rates.

The choice between cable modem or DSL will depend on what is available in your locale, and on what specific services or rates are best for you. General hardware needed for both technologies include an Ethernet card, and a high-speed modem; each ISP will specify its hardware requirements.

Security and "always on"
Both cable modem and DSL provide an "always on" connection to the Internet -- unless you specifically disconnect or turn off your computer. Leaving your computer always connected to the Internet makes it an easier target for hackers. The same precautions should be taken with your computer at home as with your computer at MIT. To make your computer more secure, be sure to do the following:

• Apply all necessary security patches to your system.
• Use strong passwords for your system and its users, and for any password-protected files or services.
• Disable any services such as file-sharing after you are finished using them.
• Keep your anti-virus software up to date, and run it regularly.

Disclaimer
MIT Information Services and Technology offers this information as a service to the MIT community, and does not endorse any particular provider. Also, IS&T does not support home networking, and cannot guarantee how remote connection to MITnet and MIT-specific applications will operate with cable modem or DSL connections.

Cable Modem

The cable modem is a device which attaches to the cable TV network connection and to your computer. This technology is being driven by cable companies to provide services beyond traditional broadcast cable TV, such as Internet access. The cable industry faces a number of challenges, including return-path capabilities (uploading), customer service issues, and standards. Potential bandwidth estimates, however, range upwards of 30 mbsp (megabits per second) from the service provider to the subscriber.

Cable networks are inherently different in design than telephone networks. Cable networks are broadcast oriented, with all subscribers in an area receiving the same signals. Lines are shared with other users, which can affect transmission speeds. Cable networks are hierarchical in nature and require two paths for data transmission: one for downloading and one for uploading. This requires either a second cable plant for uploading, or a second frequency band allocated onto the existing system.

Use of the cable modem does not affect cable TV reception, and you do not need to subscribe to cable TV service in order to subscribe to cable Internet service.

DSL

DSL (digital subscriber line) technologies use sophisticated modulation schemes to pack data onto existing telephone lines (i.e., Plain Old Telephone Service or POTS). These are sometimes referred to as "last-mile" technologies, because they are used only for connections from a nearby telephone switching station to a home or office, not between switching stations. DSL is circuit oriented so that each connection is independent of all others, giving greater consistency in connection speed.

You do not need to install a second phone line, as your existing line is split to carry phone/FAX service and DSL modem service simultaneously. With DSL you can do voice/FAX communication at the same time as data communication. Lines are not shared with other users, so transmission speeds are constant.

xDSL is next-generation technology, backed by telephone companies, to provide high-bandwidth services to homes and businesses using the existing telephone cabling infrastructure. Asymmetric Digital Subscriber Lines (ADSL), and Symmetric Digital Subscriber Lines (SDSL) are two of the more popular types of xDSL service available.

Comparing Cable Modem and DSL

The following table compares general characteristics between cable modem service and DSL service. Again, your choice of service may depend on what is available in your area. For basic information about providers in the greater Boston/Cambridge area, see High-Speed Remote Access to MITnet.

Note on fees and costs: Figures given here are for usual home rates (business rates are generally higher). Providers often offer special pricing for new subscribers, which may include free installation, discounts on monthly rates for the first few months of service, or free modems.

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