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What is ISDN?

Integrated Services Digital Network (ISDN) is a digital telephone network that provides 2 digital phone lines capable of carrying voice, data, or a combination of the two. Each digital channel can support either 64Kbps or 56Kbps* of bi-directional data and the two channels can be combined together to produce speeds of up to 128Kbps. ISDN phone lines are all digital which results in cleaner, error-free, and reliable data transmission. Analog phone lines used by modems are subject to data errors caused by line noise and other numerous transmission interruptions.

Although rarely promoted by local telephone companies and relatively unknown by the general public, unlimited ISDN service is now approximately $70/month. Considering the overall improvement of bandwidth, reliability and cost, ISDN has become a viable solution for businesses, telecommuters, and power-users who are unable to get DSL. Additionally, with local ping-times in the 60-80ms range, it's perfect for those who like to play online games.

How do I order ISDN?

Ordering ISDN is fairly easy, and it takes anywhere from 2 weeks to 2 months to get installed. If you know a few things before calling to order your ISDN line, you have a better chance of getting things right the first time. Here's how to order ISDN:

  • Make sure that XMission offers ISDN services in your area by referring to our XMission Locations page.
  • Find out if Qwest offers ISDN service in your area by visiting their webpage, or by calling Qwest's customer service.
  • Once Qwest has confirmed that your ISDN line has been installed, then purchase your ISDN terminal adapter or ISDN router.
  • If you plan on using a single 64kbps channel, you do not need to change anything with your XMission account. If you plan on using two 64k channels (for 128kbps), please call our accounting department at 801-539-0852 (or 877-XMISSION/964-7746) and ask to have "bonding" enabled. There is a charge for bonding, as you are using twice the system resources of a regular dial-up account. Please check our account information page for pricing details.

What is an ISDN terminal adapter (TA)?

An ISDN Terminal Adapter (TA) is a device that allows a computer to talk to another computer over a digital ISDN line. Like an analog modem, the TA plugs into the computer's serial port or into an internal expansion slot. ISDN TA's are ideal for single-computer situations, where you have only one computer that you want to use with the ISDN line. Terminal Adapters are very easy to install and, when compared to ISDN Routers, relatively inexpensive.

Terminal Adapters usually have 1 or 2 POTs (Plain Old Telephone) ports. These POTs ports allow you to connect analog devices (like Fax machines, analog modems, answering machines, etc) to your ISDN phone line. This way, you can use one 64Kbps channel to connect to the internet, and the other channel to send a fax or talk with someone.

One of the down-sides to the ISDN TA is their serial port speed limitation of 115.2k (12.8k slower than the 128k that ISDN has to offer). Most computers and many TA's only support 115.2k communications. Granted, this is still MUCH faster than a 56k analog modem, but you still won't realize the full 128k benefits that ISDN has to offer.

Some ISDN Terminal Adapters support 230.4k DTE rates, but most computers do not. You may want to check with your computer manufacturer and see if your computer's serial ports support 230.4k. If they do not, you may always purchase a 3rd-party add-on serial card that will do 230.4k. Companies like Lava Computer sell products like this. You can buy them locally from ComputerTech or CompUSA.

What is an ISDN router?

An ISDN router is an ethernet-based device that allows multiple computers to access to the internet via a single ISDN line. All of the computers connect to the ISDN router via an Ethernet hub, and use the ISDN router as their gateway to the internet. Whenever one of the computers makes a request for data on the internet, the router automatically picks up the line, dials, connects, and logs in (all within a few seconds!).

ISDN routers can also be faster than TAs in certain situations. A 10mbps ethernet connection to the router is almost 80x faster than the 115.2k serial port rate limitation that many PC/Terminal Adapter combinations experience. This is important when 128k of data becomes compressed, and can theoretically reach speeds of 512kbps. While these speeds can overwhelm both 115.2k and 230.4k serial ports, they are only a fraction of what a 10mbps ethernet device can handle.

Where can I get more information about ISDN?

Courier "IModem" Documentation Synapse Solutions' ISDN FAQ Qwest's ISDN FAQ