Connectivity by Rawn Shah

Communications technologies -- a peek at the next generation

In the first of a series on emerging communications technologies, we explore what's available and how the role of service providers is changing

November  1997
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This article is the start of a short series on communications technologies like DSL, ISDN, cable modems, and others: how they work, at what cost, and where they are available. You may have heard of some of them, while others may not be available in your area yet. Though none is a cure-all, most provide a viable solution for a subset of the market -- and may be the answer to your communications challenge. We start with an outline of the technologies available and a description of communications service providers and their changing roles and services. (2,000 words)

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This decade has been most interesting when it comes to developments in communications technology. Although the 1980s saw some improvements in this arena, it was not until the 90s that we actually saw active deployment of digital wireless, digital subscriber lines (DSL), ISDN, cable modems, fiber optic lines, and even satellite communications. Each is a big improvement compared to the 20-year-old analog modem and 40-year-old digital leased lines. These new technologies will contribute to the future of how we send and receive our data.

You will notice that these are transmission systems that I am talking about and not network protocols or application software. These systems provide the means for pushing raw data (bits and bytes) from one location to another. These are also more for communications outside the LAN: in the metropolitan area network (MAN), or the wide area network (WAN).


The old and the new
Before we start on the specific technologies, let us take a look at the grand scheme of things. The following two tables list the currently available technologies: Table 1 contains an older set and Table 2 the newer, more advanced systems. For each we give you an idea of the amount of bandwidth you can achieve, the distance that it can go, and what it is normally intended for.

Table 1: Current widely used transmission technologies
Technology Bandwidth Area/Distance Intended Use
Pure analog modems 300 bps - 33.6 Kbps 18,000 ft. Low-end computer data
Digital data service 56 Kbps Unlimited Low-end computer data
T-1 and fractional T-1 (E-1 in Europe) 128 Kbps - 1.544 Mbps (128 Kbps - 2.048 Mbps) Unlimited Mid-end computer conferencing data, video
T-3/DS-3 and fractional (E-2 and E-3 in Europe; J-2 and J-3 in Japan) 3.088 Mbps - 44.7 Mbps (8.45 Mbps and 34.37 Mbps; 6.3 Mbps and 32.06 Mbps) Unlimited Mid- to high-end computer data, video conferencing
X.25 2.4 Kbps - 1.544 Mbps Unlimited Low-end to mid-end computer data

Table 2: Newer transmission technologies
Technology Bandwidth Area/Distance Intended Use
ISDN 64 Kbps - 1.544 Mbps 18,000 ft. point-to-point, unlimited with ISDN central switches Voice, mid-end computer data, video conferencing
Digital subscriber lines 384 Kbps - 52 Mbps 1,000 ft. - 18,000 ft. Non- switched system. Digital television, mid- to high-end computer data, video conferencing
Cable digital "modems" 200 Kbps - 45 Mbps 2,000 ft. - 40 miles (with amplification) Mid-end computer data, video conferencing
Synchronous Optical Network (SONET) [fiber optics] 52 Mbps - 9.9 Gbps (potentially 20 - 40 Gbps) 2 km with multimode fiber, 40 km with single- mode. Unlimited with repeaters. High-speed computer data
Digital wireless telephony (PCS, CDMA) 2.4 Kbps - 19.2 Kbps 2 miles - 100 miles, unlimited when used with multiple cell towers Voice, low-end computer data
Spread spectrum wireless 64 Kbps - 45 Mbps 1,000 ft. - 10 miles Mid- to high-speed computer data
Ku-band satellites 16 Kbps - 2 Mbps Unlimited Low- to mid-end computer data
Ka-band satellites 400 Kbps - 155 Mbps (potentially 1 Gbps) Unlimited Mid- to high-end computer data, digital television

If you are heavily into WAN communications, you will notice that we did not include every single type of transmission system available. Well, that isn't always possible and some of the ones not listed here are simply variations of the ones listed here. For example, frame relay is really more of an abstraction of higher levels of the data link layer; it can work at various different speeds and can even use several different types of transmission systems ranging from 56-Kbps DDS to 45-Mbps DS-3, although most still equate it with T-1s. Another example is asynchronous transfer mode (ATM) connections which are essentially specialized SONET links running ATM cells over them instead of something else like native TCP/IP on SONET. On the other hand, in our "newer technologies" table, there are so many different varieties of spread spectrum technology, it would be hard to list them all; most are proprietary and only interoperate with other products from the same vendor although all are based on similar concepts.

Also, you will notice that we did not put any indication of prices or the areas of availability of these services. The price for some of these services vary greatly depending on where you go. For example, an X.25 line in Africa can cost up to the equivalent of several thousand dollars a month for a basic 19.2-Kbps link; on the other hand, it can cost a few hundred dollars on the east coast of the U.S. In other cases, a T-1 in Southern California can cost $500, whereas in Central Arizona, it can cost $2,500 (keep in mind these are only line charges and not ISP or other charges). It greatly depends on your location and the distance between the points of communication. Don't be fooled by such generalized statements like, "A T-1 costs $1,000/mo in the U.S."

Prices for some of these services are also dependent on the service provider in your area and the regulatory commission. Although they can charge more or less (we can hope), they are required to stay at a certain level for some services. For example, Pacific Bell has been authorized to sell BRI ISDN service around $25/mo whereas US West can charge around $60/mo.

In some states and countries the newer technologies may not be available for financial, administrative, or political reasons. What the service provider says they have and what they will actually provide are quite different. Take DSL for example. It is not widely available in many regions in the U.S. for the following three reasons: It's expensive to introduce; there aren't sufficient technical and business administration facilities yet; and many local exchange carriers (LECs are your local phone companies) don't want to provide it because it affects the sales of other products (like their lucrative T-1 business).

Service providers: their changing role
Let's familiarize ourselves with the different types and levels of service providers (SPs). For now we are going to ignore higher levels of service like Internet service providers (ISPs) because we are only talking about transmission systems.

An SP has the legal, financial, and technical capability to bring a physical connection between two points within its territory or provide you with an interconnect to an intermediary or foreign SP outside its territory. In the U.S., telecommunications for the voice industry and part of the data communications industry used to be strictly regulated. This was done to prevent any single massive monopoly like the old Bell system from developing. This has all changed over the years and in 1996, Congress released a new Telecommunications Act allowing greater freedom in telecommunication vendors territory and type of service. Previously you had a strict division between local and long distance industry and industries such as cable and voice/data. The restrictions have now been lifted to allow companies to invest in these other services as well.

In the international market it gets more complex. The case is different in many countries, but the majority of the world's nations have a government-controlled or subsidized monopoly on communications with little or nascent competition. Such a monopoly ensures a common service level and availability to all citizens; unfortunately, it also introduces government bureaucracy and politics into the issue. In countries like Japan and some European nations, this is different. Also many modern countries's international and multinational telecommunications SPs are making serious inroads in the global data communications market. Some technology areas like DSL may never open up to international competition because of locality; however, others, especially high-speed communications, are becoming common. Moreover, satellite communications is promising to bring a new level of open communications availability across every single square foot of the globe.

Back in the U.S., with the new Telecommunications Act, some SPs are already consolidating their territories and services together to better survive in these days of decreasing profit margins on services. Already we are hearing news stories such as Pacific Bell joining SBC to form a newer multistate phone company, or even the latest multibillion dollar MCI- British Telecom-WorldCom-GTE dance of the merging companies. In some cases, companies are jumping into other markets like TCI and Time-Warner Interactive providing data and voice services over their large collection of cable plant systems in towns and cities across the U.S.

Competing technologies
To make matters more complicated, many of these newer technologies not only compete with the older ones but with themselves as well. There are several markets to consider:

Financially, for the vendor, each of these markets means something completely different even if they use the same technology. This is where business matters come in to affect price and availability. Some, like the local low-end, local high-end, and wide-area items, are established markets undergoing a shift in implementation. Instead of DS-3s, companies are investing in SONET OC-3Cs. And instead of analog modems, users are buying ISDN "modems." Other technologies like digital voice and telephony have just emerged within the past few years with the wide acceptance of cellular phones. Still others like digital television and video conferencing are barely in trial stages but hold a very important future.

To give you an idea of how the markets are faring take a look at the following estimates of revenues in the telephone, wireless, and cable TV markets in the U.S.:

Table 3: Communications revenues
Service Type 1994 ($ billion) 1998 est. ($ billion)
Local voice calls 41 49
Long distance voice 16 18
Data networks 28.7 29.6
Wireless 15 25
Cable TV 25.5 35
(Source: "Video Dialtone Technology," D. Minoli, 1995)

Anyone can see why some SPs will want to get into certain areas -- soon. Apparently, the grass is always greener on the other side. In following the technologies employed in their current markets, these SPs are trying to take what they are familiar with to these other markets rather than make huge investments into completely different systems. Hence, what you see are telephone companies investing in DSL and SONET and cable companies looking at cable modems and satellite services.

Now that you have seen what these technologies are and who the players are, we can go on to talk about the specifics of these systems. In this continuing series of columns, we will pay closer attention to how some of these newer technologies work and how they are offered from a business perspective. We will also talk about higher-level services and variations of these that are publicly available.


About the author
Rawn Shah is vice president of RTD Systems & Networking, Inc. He has worked with many different aspects of the LAN world and is currently strongly investigating the world of ATM and DSL and their implementation and implication on the future of voice, video, Internet, and data networking. Reach Rawn at

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