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). 

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. 

Cable and DSL have both proven to be simpler, cheaper, and faster than ISDN !!

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.



Speed and Bandwidth
Speed and bandwidth are very important considerations when choosing a service. Speed refers to data transmission rate. Bandwidth is the capacity to carry data. Both are measured in bits per second. PRI ISDN can deliver data at rates from 128 Kbps to 384 Kbps. DSL, with its many flavors, offers much faster rates and more bandwidth for downloading files. DSLs data rates range from 128 Kbps to 8Mbps, depending on the DSL flavor you choose.

Installation: Wiring
Both ISDN and DSL work over the ordinary twisted pair copper wires that are located behind your walls. For DSL, your service provider may need to install new wire depending on the type of DSL flavor you want. Generally, ISDN installations do not require wiring upgrades.

Dial-Up and Always-On Service
ISDN is a dial-up service. To make your connection to the Internet, you must dial a phone number. The connection is ended when the caller hangs up. There is a version of ISDN that is always connected without dial-up. It is called Always On/Direct ISDN (AO/DI). If you are interested, you will have to buy both an AO/DI modem and a Dial-Up Networking Patch for Windows. You will also need to use a service provider that supports AO/DI.

DSL does not require a dial-up. Once your business has installed DSL, your service is "always on" and youre always connected.

Both ISDN and DSL are used for carrying voice, data and video at fast rates. They are both used to access the Internet, and download/upload large files quickly. Video conferencing can also be accomplished with both services.

Special ISDN Uses
If any of the following applications are practical for your business, then you may wish to consider choosing ISDN over DSL. Emerging Technologies: New DSL Products
Many new and exciting DSL products will be introduced into the marketplace soon. These products may be particularly suitable to your needs. Heres some examples of developing DSL products: Required Equipment
Unlike DSL, ISDN does not require a special modem. However, if you are going to use ISDN for high-speed Internet access for data and video transmissions, youll need a terminal adaptor to connect the line to your PC. If your network users are "sharing" the dedicated line in your network, youll need an ISDN router.

For PCs, the UART chip for the PCs serial port should support ISDNs speeds. If it does, you can use an internal ISDN card or external ISDN terminal equipment. If it does NOT, youll need to consider an internal ISDN card to bypass the slower PC port. If you are using Windows 3.1 or Windows for Workgroups, youll need to make sure your ISDN terminal equipment includes an ISDN-compatible dialer.

For Macs, youll need an internal ISDN card or external ISDN terminal equipment. MacOS 7.5.3 (and earlier) requires installation of the SerialDMA driver for faster throughput when using external ISDN terminal equipment.

For DSL, a splitter is usually required, depending on the flavor of DSL you want, or the type of DSL available in your area. G-Lite DSL does not require a splitter. A DSL modem and an Ethernet card are also required for installation.

Unlike your analog telephone line, your DSL line does not draw its current from your local service provider central office. Youll need an Uninterruptible Power Supply (UPS) to ensure continuous service in the event of a power failure.

DSL use requires that your computer have a Peripheral Component Interconnect (PCI) slot for installing the PCI. PCI adaptor cards may also be necessary to combine an Ethernet interface to your PC with DSL modem functions.

Cost and Value Considerations

ISDN is a premium service based on usage. Costs will vary, depending on your own particular use. ISDN routers may need to be installed. Setup and installation will probably be your biggest out-of-pocket expenditure. If you are building a fairly large network, ISDN may be a good choice for your business. An alternative to ISDN with a very large bandwidth is Asymmetric Digital Subscriber Line (ADSL).

DSL is a very affordable and cost-effective service based upon a flat rate. Since cost is not based upon usage, you can use this service any time for as long as you want without incurring any usage charges. It is easily and inexpensively installed. In fact, you may be able to install it yourself. However, you will need to purchase a DSL modem, a splitter and an Uninterruptible Power Supply when installing service. When selecting DSL, you should determine which flavor of DSL is best for your business. This decision will affect the price of DSL installation and service.

For businesses that need the high-end flavors of DSL with very large bandwidth and ultra fast speeds, techniques are currently being developed that will lower costs for installation, deployment, testing and maintenance of these high-speed services. By reducing or eliminating the need for additional central office switching equipment, these new products can also cut the deployment time for these new high-end services.