Some articles about ISDN leave the reader with the feeling of "I Still Don't kNow". Here is a practical guide intended to explain ISDN and what it means to you. ISDN stands for Integrated Services Digital Network. ISDN was conceived in the late-sixties/early-seventies by the CCITT. (Consultative Committee for International Telegraph and Telephone). It gestated during the eighties and is now being realized (in North America) in the nineties. Before I get into the details, here's a summary list of the basic capabilities of ISDN:
These original principles of ISDN still hold true today. For example, multimedia (voice, data, image) and open standards (limited set of standardized interfaces) are still prime movers in today's converging telecommunications, computer, entertainment, and information industries. However, it is necessary to recognize two distinct stages of ISDN evolution.
Narrowband ISDN: Today's implementation of ISDN is based on the original ISDN specifications. This (here and now) stage is commonly referred to as Narrowband ISDN. Narrowband refers to the electrical transmission of information over copper-based telephone lines at speeds of up to 1.5 Mb/s (Megabits per second), usually in increments of 64 Kb/s.
Broadband ISDN The upcoming implementation of ISDN is referred to as Broadband ISDN. Broadband ISDN will be more appropriate for today's concepts of multimedia, (multimegabit bandwidth) video and interactive services. Broadband refers to higher speed communications (typically from 45 Mb/s to 622 Mb/s) over fiber optic network access and transport lines.
This article describes salient aspects of the Narrowband ISDN. The three primary concepts embodied in the CCITT definition of ISDN are described below:
The early ISDN architects adopted digital encoding and transmission schemes to overcome this condition. Even with today's sophisticated error-correcting modems, the local access (local loop) portion of the telephone network is still susceptible to induced noise. This causes degraded transmission efficiency and poor data quality primarily because of the underlying analog encoding and transmission scheme.
Today's sophisticated error correcting modems (with compression techniques) are limited to the 30 to 50 Kb/s range over the conventional public telephone network. Because of its inherent digital encoding and transmission scheme, ISDN provides virtually error-free transmission at higher speeds up to 1.5 Megabits/second. These speeds are achieved without compression. Still higher throughput will be obtained with ISDN-based transmission devices that incorporate compression. (Ratios could range from 2:I to 6:1.)
The BRI provides a total transmission bandwidth of 160 Kb/s. The 160 Kb/s is divided between overhead, signaling/control and user (Bearer) information. Of the 160, 16 Kb/s is dedicated to overhead. This includes data organization (framing) and an embedded operations channel for network maintenance and performance management functions.
This leaves 144 Kb/s available for control and user information. The 144 Kb/s bit stream is logically partitioned into two 64 Kb/s "Bearer" (B) channels and one 16 Kb/s signaling/data (D) channel. Hence, the BRI is often referred to as "2 B + D". The D channel always carries control/signaling information but can also simultaneously support an X.25 Packet-Switched Data Bearer service with throughput of up to 9.6 Kb/s. Bearer (B) channels carry user information and can be assigned to any of the following (Bearer) services:
The PRI provides a total bandwidth of 1.536 Mb/s. The PRI bitstream is partitioned into 23 user-assignable 64 Kb/s logical B channels and one 64 Kb/s logical D channel which only supports user-to-network signaling. The PRI is targeted at "high speed" bulk information transfer and high call volume applications. This includes such host-to-host file transfers, group video conferencing, remote computer aided design/ computer aided engineering workstation access and Private Branch eXchange (PBX) network access.
The open-standards-based D-channel protocol is the key to the flexibility and utility of the (BRI and PRI) ISDN interfaces. Because the D-channel protocol is derived from X.25, it inherits the X.25 multiplexing technology that allows simultaneous logical "sessions" over a single physical interface. This allows multiple calls and call types (i.e., VI, CSD, and PSD) to exist simultaneously on a single ISDN line.
The ISDN equivalent of a modem is called a Terminal Adapter, which is dramatically different from a modem. Because ISDN capable equipment delivers digital information to your telephone jack, analog/digital conversion is not necessary. The computer modem will eventually be replaced by an inverse multiplexer. This will act as a data separator to route data to your computer.
In November of 1992 the first version of this standard was successfully demonstrated. Since then, actions have been taken to increase ISDN availability by:
1) Tariff agreements for ISDN serviceAdditional work is underway with computer industry giants like Microsoft and Intel to define Applications Programming Interfaces. The net result of these and many other activities is that technical obstacles to widespread national ISDN availability are being swiftly overcome.
2) Nationwide interconnection agreements between long distance voice and data carriers.
3) End-user equipment manufacturers working together to provide high quality, low cost ISDN terminal equipment.
(By Matt Young)
ISDN is a digital dial-up telephone service technology that does not require modems. ISDN operates 5 to 10 times faster than current modem technology. ISDN is widely available now for businesses, but not to home users. Upgrades to telephone company equipment are necessary before offering digital dial-up service to the consumer. These upgrades are not yet completed in suburban areas.
Rate adaption is one of the many ISDN standards. Rate adaption allows multiple low speed data streams between two sites over a single ISDN telephone line. For instance, an office site could connect to both an email and a database service from the headquarter's office over a single digital telephone link.
The next ISDN rate adaption specification was called Frame Relay. Multiple bytes from one source are packed into a single frame and sent to one destination. Then another frame of bytes is packaged for the second source, and so on. The frames (data packets) look like streamlined X.25 packets, but with only half of the header information. Frame Relay is very popular and today users can obtain frame relay service from most public packet networks. The Frame Relay is a competitor to X.25.
The third rate adaption specification is called Time Division Multiplexing (TDM). The digital data stream is broken into bytes, and bytes are assigned to each source. The first source uses bytes 1 and 2, the second 3 and 4, and so on. This is the current form in which traditional phone calls are packed into high-bandwidth links for long distance transmissions.
Yet another method to implement rate adaption is called fast switching. Fast switching maintains two or more connections through a network. The end user's software tells the network to direct the data stream to one of the connections. The data stream follows the requested path until the software indicates that the stream should be redirected. A convenient feature of fast switching is that if only one connection is established, the data stream behaves like a 'normal' modem connection.
Fast switching depends upon having another frame-based rate adaption technique. This other technique allows requests and responses between the network connection controller and the user's software.
Are the telephone companies going to be the ones to make this work? Maybe not. Internet and Tymnet use this technology now, but their methods are not optimized for BBS users. Because of the growing importance of online operations, the industry is beginning to take a look at rate adaption standards optimized for high speed modems. You can be sure that any standards will be compatible with all current software, and all current and planned modems.
However, for the uninitiated, the unwilling, and just about anyone else outside of the techno-fraternity (90% male according to my BBS statistics), the BBS menuing system can be confusing, intimidating, and obscure to the point of frustration. The best we (as Sysops) could do for our novice users was to use ANSI colors and simplified layouts in an attempt to make the "What do I do now?" question as self-answering as possible.
The luckiest novice callers would have a mentor/guru at their side (or at least one only a phone call away). The rest had to suffer with vague help screens full of techno-babble.
New BBS callers can be intimidated by online menus full of BBS jargon. I have watched people on my own system give up half way through the new user questionnaire when they were asked to "Please select a default download protocol".
Who knows what a default download protocol is? Some of my users didn't even understand the full implication of what "default" meant, let alone what a "protocol" is. I have, of course, changed that question since then, but you get the idea. RIP allows almost all of this "techno-speak" to be either eliminated entirely, or learned at a much slower "learn as you BBS" pace. The key is to eliminate the traditional BBS menuing system and move to a point and click interface.
The number of people who are "Command Line Impaired" is huge. However, the number of "Mouse Enabled" people is growing faster than ever before, due to the wide spread acceptance of Graphical User Interfaces on all platforms (even Unix!).
RIP will allow all types of BBS software packages to appear to be the same to the callers. The caller will be spared from having to remember the differing commands for each type of BBS software.
With RIP, the caller only needs to click on the New Personal Mail button, regardless of the underlying BBS system software. The same buttons will do the same thing on all RIP-compatible systems. BBS software authors may not like it, but RIP will remove the BBS software specific "flavor" from most packages, much to the caller's delight!
Locally stored icons use a small amount of disk space. If you call 10 RIP BBSs, you're going to have 10 sets of icons stored on your hard disk. RIPTerm itself installs 500K of icons - which provides most of the icons that will be used. Additional storage demands should be minimal, depending on how "RIP Happy" your Sysop gets.
The tools and software for RIP BBSs are less than three months old, but already I am seeing virtually every BBS package announcing RIP compatibility. To give you a "Taste of RIP", download RIPTM153.EXE and call any v3.9 Wildcat BBS. Many other BBS software companies are also starting to support RIP.
Page 29 was a full-page ad for Halted Specialties, Inc. (www.halted.com)
Page 30 (back cover) was a full-page ad for TeleText Communications.
End of Issue 7. Go back, or to Issue 8, or to Mark's home page.