DSL

DSL stands for "Digital Subscriber Line" and is a technology that transforms ordinary copper phone lines into digital lines for high-speed Internet access. The use of digital coding techniques and DSL modems enables high-speed Internet access -- usually without installing a second phone line.

DSL technology is available in several forms, collectively referred to as xDSL. With ADSL (Asymmetric Digital Subscriber Line), the download speed is faster than your upload speed, and this usually fits the way most people use the Internet. Speed is optimized at up to 1.54 Mbps or more down (getting things off the Internet) and the upload speed is up to 384 Kbps. For comparison, dial-up connections have a speed of 33.6 Kbps or at best 53 Kbps.

DSL is often among the fastest types of connection available to University customers. However, it is not portable and is more expensive than analog connectivity options, though recently pricing has become far more competitive. High-speed services such as DSL are still maturing and may not be the ideal choice for everyone. We encourage you to investigate your options and be aware of the issues and possible complications that go along with DSL service. For example, DSL installation can take several weeks to complete and may require multiple visits from both the phone company and the DSL provider.

For more information on DSL, try reading Everything DSL or Broadband Reports.

Verizon (800) 567-6789
SpeakEasy (800) 556-5829

Cable Modem

A cable modem is an external device that allows your computer to connect to the Internet through a cable TV wire, instead of a telephone line (or other system). Cable modems translate radio frequency (RF) signals to and from the cable plant into Internet Protocol (IP), the communications protocol spoken by all computers connected to the Internet.

The cable modem has two interfaces: a standard "F" port connector and a 10Base-T Ethernet RJ-45 port. The PC attaches to the cable modem via the 10Base-T Ethernet cable. The "F" connector attaches to the same cable that provides the video signal to your television/VCR. When attached to a two-way cable system, the modem will send and receive data via the cable. The downstream (network to home) channel will occupy a single 6 MHz (standard CATV) channel within the Radio Frequency (RF) spectrum -- 54 to 750 MHz. Advanced modulation techniques allow data to travel as fast as 36 Mbps on a single 6 MHz analog carrier. To avoid consuming too much of the CATV spectrum on the "upstream" return, several cable modem manufacturers haved esigned their products to use less than a full 6 MHz carrier out of the home. The cable runs from your neighborhood to a central location, referred to as the headend. Additional equipment is installed there that communicates to all the cable modems in subscribers' homes.

For those who can get it in their area, cable modem service has quickly become a popular high-speed alternative due to competitive costs and very high speeds.

Comcast (800) 266-2278
Time Warner (Road Runner) (866) 829-7772

Dial-up

Analog modems (MOdulator-DEModulatorS) are devices that convert a computer's digital information into audio frequencies (analog) for the telephone system and convert the audio frequencies back into digital information at the receiving side. Modems also dial the number, answer the call, and control transmission speed.

All new modems have built-in error correction (V.42) and data compression (V.42bis, MNP 5). On files that are already compressed, the hardware data compression adds little value, because it cannot make compressed files smaller. Modems also have automatic feature negotiation, which adjusts to the other modem's speed and hardware protocols.

Analog modems are slow compared to DSL, Cable, and ISDN, but are fast enough for many users, require the fewest changes, and are the least expensive of any of the remote access connectivity options.

Penn-Preferred Dial-Up Service Providers

DCANet (888) 432-2638
NavPoint (215) 836-4600
Quadnet (215) 322-2300

Other Considerations

ISDN Service Offerings (when DSL or cable are not available)

ISDN (Integrated Services Digital Network) is a telecommunications standard for transmitting voice, video, and data over digital lines running at 64 kbps.

ISDN uses 64 kbps circuit-switched channels, called B channels, or "bearer" channels, to carry voice and data. It uses a separate D channel, or "delta," channel for control signals. The D channel is used to signal the telephone company computer to make calls, put them on hold and activate features such as conference calling and call forwarding. It also receives information about incoming calls, such as the identity of the caller.

ISDN's basic service is Basic Rate Interface (BRI), which is made up of two 64 kbps B channels and one 16 Kbps D channel (2B+D). Both B channels can be combined into one in a process called bonding, which doubles the total data rate to 128 kbps.

ISDN is noticeably faster than analog modems but significantly slower than DSL connections. ISDN can be installed in almost any location in the tri-state area, but is not portable. ISDN has fallen out of favor in comparison with DSL and cable, as it is an aging, slower technology.

upenn.talk.isp

There is a newsgroup devoted to further discussion about experiences with ISPs which you are encouraged to read and participate in at upenn.talk.isp.