Cable vs DSL vs ISDN
*** a technical overview of each ***
For many years, corporations were the only ones who could afford high-speed Internet access. The common citizen was relegated to using slow, dial-up. Although there are still millions of dial-up users (just ask AOL and Earthlink), Cable and DSL are rapidly taking over, with their blazing speeds. There really is no comparison, and if you are on dial-up and your area has cable or DSL . . . switch !!
Here we briefly describe the services and then compare them:
Description of the Three Services
Cable, like DSL, supports different speeds for sending and receiving data. Upstream speed on cable networks is generally rated at 128 Kbps, but you can purchase up to 512 Kbps of upstream throughput. For most businesses 512 Kbps is more than enough. Most people are generally only sending requests to the Internet and downloading information to their computers. This makes the downstream capability more important, and cable offers downstream speeds up to 10 Mbps. Most of us will generally get between 0.5 Mbps and 3 Mbps while surfing the Web. One of the advantages of cable over DSL is that it is available to all users inside a cable company's cable network, and not limited to a specific distance from a central office.
DSL (Digital Subscriber Line)
Unlike cable, DSL is provided by the telephone company over your existing copper wire. With DSL, you can get both voice and data over the same pair of wires. Unlike cable modems, most DSL implementations only allow you to send and receive data anywhere from 144 Kbps to 1.5 Mbps, depending on the type of DSL service available in your area. One of DSL's biggest limitations is that it is only capable of delivering its higher-speed data access to users within 18,000 feet of the telephone company's central office.
Unlike ISDN, DSL is an "always on" digital service. To connect, you never have to dial-up. There is only one path for carrying voice, video and data. There are two flavors of DSL that are widely being used today: Symmetric DSL (SDSL) and Asymmetric DSL (ADSL). The difference between them is their ability to carry data in upstream (i.e., upload) and downstream (i.e., download) directions. SDSL uses upstream and downstream capacity to carry data in both directions. ADSL delivers higher speed downstream service, and slower speed upstream service. If users at your business spend more time downloading files than uploading files, you may choose ADSL since you can download pages faster.
ISDN (Integrated Services Digital Network)
ISDN, often jokingly referred to as "I Still Don't Know", like DSL, is a digital telephone line provided by the telephone company. It was an interesting concept, because it uses the telephone company's switched voice network to send data across. Like DSL, you must be located within 18,000 feet from the telephone companys central office (CO) to get this service.
Line Conditioning and Load Coils - standard POTS (Plain Old Telephone System) lines cannot carry ISDN, because they have inductors, placed every 1000 feet or so . . . called Load Coils, placed in serial with the lines - to reduce noise. That's great for voice, but inductors inhibit high frequencies, which are needed for digital signals. Therefore, for every ISDN line, all the load coils must be either removed or bypassed. This is called line conditioning, and is a major headache.
The two Types of ISDN
ISDN comes in two flavors - BRI (Basic Rate Interface) and PRI (Primary Rate Interface).
- BRI is 2B+D. It has two 64kbps "B" channels for data, and one 16k D channel for signaling.
- PRI is 23B+D. It has 23 64k B channels, and 1 64k D channel.
ISDN is a switched digital dial-up service. It combines video, voice and data on a single access line. Basic Rate (BRI) ISDN is generally for home use and has three channels. Primary Rate Interface (PRI) ISDN is the business version of ISDN and has 24 channels, or paths. It uses 23 B channels for carrying voice, video and data on the same copper wire. Channel 24, the D channel, is used for carrying low speed data communications, switching, and signaling. This signaling is what produces the ringing of the phone, busy signals, alarm signals, and other non-voice functions. ISDN cannot transmit video or data to analog lines. Some of your customers may need special ISDN equipment to receive certain data files sent by your business.
ISDN was originally made for point-to-point switched digital calls - not as an Internet access method. Many small companies bought ISDN instead of expensive T1 (also point-to-point but they stayed ON 24x7) connections, because they could dial-up their sister site, transfer files or use long-distance applications, and then when finished - disconnect. But if someone forgot to disconnect, and left the connection up for the weekend - huge fees resulted !!
Later, as ISDN came down in price - it became somewhat popular as an Internet access method. But still, it only brought users up to 64k (most ISP's did not offer the faster 128k ISDN speed), and most already had 56k - so it never was a big seller.
A few years ago, in answer to slow dial-up, ISDN was slated to be the final answer to high-speed Internet access with voice on one line. But DSL and Cable have now eclipsed ISDN by a huge margin.
Simpler - ISDN is difficult to setup - so difficult, that for years, many techs were simply unable to install it
Cheaper - ISDN is not a flat fee. It is usage-based (per minute). It typically costs anywhere from $70 to $200 for installation, and then
ISDN is a phone call that communicates with digital data instead of analog voice.