ISDN ........... Zoom!

[reprinted from IEEE - Fort Worth Section Signals December 1995]

by Jeff Carrell, Electronic Communications Chairman

Want to communicate *fast* to the Internet or other computer networks, then consider ISDN, it's 4 times faster than 28.8Kbps dial-up.

ISDN Starting Point:

Integrated Services Digital Network (ISDN) is not something you talk about at parties, nor at the coffee break at work, but soon it might be. In order to make use of this faster communications medium, you'll need the following: hardware, software, ISDN telephone service and Internet ISDN service.

ISDN is digital telephone technology that has been in existence since 1984, but its practical deployment has only occurred in the last three years (actual date: 11/16/92). ISDN provides data rates from 64Kbps up to 1.5Mbps and is broken down into two basic types: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). Each type has a number of 64Kbps bearer (B) channels and one data (D) channel. B channels are used for voice and/or data connections and the D channel is the call setup and signaling/control side of the link. BRI has two B channels and one 16Kbps D channel (2B+D) and PRI has 23 B and one 64Kbps D channel (23B+D). BRI is the most common for home or minimal business use, based mostly on price.

BRI can be used to link at 128Kbps speeds, depending on the type of equipment and service you get. So you may want to decide ahead of time how much bandwidth you need, before purchasing equipment or signing a contract for Internet service. ISDN can even be used for voice phone calls, but remember if you want that nice crisp digital sound, the party your calling must also have ISDN, or your using ISDN like an analog line.

When using ISDN, you actually dial a phone number just as if you were calling a 'normal' phone line, it just happens to be a digital line your calling. When using ISDN for "home" use, the service from some Internet providers is called "Dial-up ISDN" as opposed to full-time network connections, sometimes referred to as "LAN or Network ISDN".

Some basic differences between ISDN and dedicated leased lines are: ISDN is dial-up technology, thereby not requiring equipment to maintain a full-time connection; it can dynamically mix data and voice based on the call type; it provides for dynamic bandwidth (based on equipment and service type); and most importantly, it is much cheaper per month.


Connecting ISDN to your computer is not difficult, but you cannot use the same modem you've been using. There are ISDN "modems" but they are referred to as terminal adapters (TA). They convert the serial communications (RS-232) from the PC to ISDN. TAs come in various configurations: ISA/EISA/MCA internal adapters, PC Cards (formerly known as PCMCIA) for notebooks and external standalone units that connect to your PC's RS-232 interface connector. The starting price for a TA is about $600.

Once you have the PC side of the hardware, you must have the phone company side of your equipment. SWBT will terminate the ISDN service to your house (usually the outside box), but you must then connect your own network terminator 1 (NT1) to the jack. The NT1 multiplexes and also converts from the 2-wire telco line to the 4-wire ISDN signal from the TA. NT1s are a bit less expensive than TAs, starting at about $200.

There are a few manufacturers now integrating both the TA and NT1 into a single device with costs starting at about $500. You can purchase the TAs, NT1s or the combination unit from SWBT for fairly reasonable prices or purchase them from an alternate source, so shop around before buying.


As in any PC, hardware always requires more (or different) software. You basically need a communications package that will work with an ISDN card or interface unit, just like you do for a serial modem, and support for Serial Line Interface Protocol (SLIP) or Point-to-Point Protocol (PPP). If you are using Chameleon from NetManage (some versions) for Internet communications now, you can still use it for ISDN. Otherwise, there are other commercial as well as shareware communications packages that have ISDN support.

Phone Company Issues:

In the DFW metroplex, SWBT charges $57.90/month for BRI, with a (steep) one-time installation charge of $578.00. However, the benefit they have over many other ISDN providers is no usage fees in addition to the monthly charge. You pay the flat rate (just like a "regular" phone bill) whether you use it 5 minutes or 500 hours a month. SWBT also offers NT1, TA and NT1/TA equipment for sale. This one-stop shopping does make for an easy task of obtaining ISDN service and needed hardware to complete your physical connection.

ISPs Supporting ISDN:

Of the almost two dozen Internet Service Providers (ISP) in the DFW area, only a few offer (today) ISDN support. Of these, the monthly fees and setup charges vary substantially:

ISP              1B Channel   2B Channel 128K    Setup    Notes                    

OnRamp             95.00           195.00      95.00/195  1B/2B-LP - if only one   
                                                          line is open,            
                                                          connection is made at    
                                                          64K, otherwise           
                                                          connection made at 128K  
                                                          - 145.00/145.00          

CompuTek           24.95           59.00           *                               

Internet           49.00           99.00       0.00/99.00 120 hours per month      

CyberRamp          69.95           119.95          *                               

PSI                29.00           29.00           *      29 hrs/14.5 hrs          
                                                          included in prime time,  
                                                          extra per hour charges   
                                                          of 1.50/3.00 afterward   

* - contact ISP directly for pricing information

ISDN Info Sources:

Many places on the 'Net have resource information on ISDN. Try some of these web pages: the best on ISDN with many links to other places! the Texas ISDN Users Group in Austin look for the BitSURFER Pro excellent ISDN Technology Paper

General Info:

Have a question or want to know more details about e-mail, the Internet electronic communications or related technologies? Send a note to me or Signals editor we will cover it in a future article.

If your society, company or other organization would like an Internet presentation, demo, discussion, etc., let me know. (no commercial pitch, just plain 'ole techie talk :-)


snail-mail: Jeff Carrell POB 1593 Hurst TX 76053

phone/fax: 817.595.0343

Copyright 1995 Jeffrey L. Carrell. All Rights Reserved