Many network vendors and suppliers exist, each with its own ideas of how things should be done. Without coordination, there would be complete chaos, and users would get nothing done. The only way out is to agree on some network standards.
Not only do standards allow different computers to communicate, but they also increase the market for products adhering to the standard. A larger market leads to mass production, economies of scale in manufacturing, VLSI implementations, and other benefits that decrease price and further increase acceptance. In the following sections we will take a quick look at the important, but little-known, world of international standardization.
Standards fall into two categories: de facto and de jure. De facto (Latin for ''from the fact'') standards are those that have just happened, without any formal plan. The IBM PC and its successors are de facto standards for small-office and home computers because dozens of manufacturers chose to copy IBM's machines very closely. Similarly, UNIX is the de facto standard for operating systems in university computer science departments.
De jure (Latin for ''by law'') standards, in contrast, are formal, legal standards adopted by some authorized standardization body. International standardization authorities are generally divided into two classes: those established by treaty among national governments, and those comprising voluntary, nontreaty organizations. In the area of computer network standards, there are several organizations of each type, which are discussed below.
Who's Who in the Telecommunications World
The legal status of the world's telephone companies varies considerably from country to country. At one extreme is the United States, which has 1500 separate, privately owned telephone companies. Before it was broken up in 1984, AT&T, at that time the world's largest corporation, completely dominated the scene. It provided telephone service to about 80 percent of America's telephones, spread throughout half of its geographical area, with all the other companies combined servicing the remaining (mostly rural) customers. Since the breakup, AT&T continues to provide long-distance service, although now in competition with other companies. The seven Regional Bell Operating Companies that were split off from AT&T and numerous independents provide local and cellular telephone service. Due to frequent mergers and other changes, the industry is in a constant state of flux.Companies in the United States that provide communication services to the public are called common carriers. Their offerings and prices are described by a document called a tariff, which must be approved by the Federal Communications Commission for the interstate and international traffic and by the state public utilities commissions for intrastate traffic.
At the other extreme are countries in which the national government has a complete monopoly on all communication, including the mail, telegraph, telephone, and often, radio and television. Most of the world falls in this category. In some cases the telecommunication authority is a nationalized company, and in others it is simply a branch of the government, usually known as the PTT (Post, Telegraph & Telephone administration). Worldwide, the trend is toward liberalization and competition and away from government monopoly. Most European countries have now (partially) privatized their PTTs, but elsewhere the process is still slowly gaining steam.
With all these different suppliers of services, there is clearly a need to provide compatibility on a worldwide scale to ensure that people (and computers) in one country can call their counterparts in another one. Actually, this need has existed for a long time. In 1865, representatives from many European governments met to form the predecessor to today's ITU (International Telecommunication Union). Its job was standardizing international telecommunications, which in those days meant telegraphy. Even then it was clear that if half the countries used Morse code and the other half used some other code, there was going to be a problem. When the telephone
was put into international service, ITU took over the job of standardizing telephony (pronounced te-LEF-ony) as well. In 1947, ITU became an agency of the United Nations.
ITU has three main sectors:
- Radiocommunications Sector (ITU-R).
- Telecommunications Standardization Sector (ITU-T).
- Development Sector (ITU-D).
ITU-T has four classes of members:
- National governments.
- Sector members.
- Associate members.
- Regulatory agencies
ITU-T's task is to make technical recommendations about telephone, telegraph, and data communication interfaces. These often become internationally recognized standards, for example, V.24 (also known as EIA RS232 in the United States), which specifies the placement and meaning of the various pins on the connector used by most asynchronous terminals and external modems.
It should be noted that ITU-T recommendations are technically only suggestions that governments can adopt or ignore, as they wish (because governments are like 13-year-old boys—they do not take kindly to being given orders). In practice, a country that wishes to adopt a telephone standard different from that used by the rest of the world is free to do so, but at the price of cutting itself off from everyone else. This might work for North Korea, but elsewhere it would be a real problem. The fiction of calling ITU-T standards ''recommendations'' was and is necessary to keep nationalist forces in many countries placated.
The real work of ITU-T is done in its 14 Study Groups, often as large as 400 people. There are currently 14 Study Groups, covering topics ranging from telephone billing to multimedia services. In order to make it possible to get anything at all done, the Study Groups are divided into Working Parties, which are in turn divided into Expert Teams, which are in turn divided into ad hoc groups. Once a bureaucracy, always a bureaucracy.
Despite all this, ITU-T actually gets things done. Since its inception, it has produced close to 3000 recommendations occupying about 60,000 pages of paper. Many of these are widely used in practice. For example, the popular V.90 56-kbps modem standard is an ITU recommendation.
As telecommunications completes the transition started in the 1980s from being entirely national to being entirely global, standards will become increasingly important, and more and more organizations will want to become involved in setting them. For more information about ITU, see (Irmer, 1994).
Who's Who in the Internet Standards World
The worldwide Internet has its own standardization mechanisms, very different from those of ITU-T and ISO. The difference can be crudely summed up by saying that the people who come to ITU or ISO standardization meetings wear suits. The people who come to Internet standardization meetings wear jeans (except when they meet in San Diego, when they wear shorts and T-shirts).ITU-T and ISO meetings are populated by corporate officials and government civil servants for whom standardization is their job. They regard standardization as a Good Thing and devote their lives to it. Internet people, on the other hand, prefer anarchy as a matter of principle. However, with hundreds of millions of people all doing their own thing, little communication can occur. Thus, standards, however regrettable, are sometimes needed.
When the ARPANET was set up, DoD created an informal committee to oversee it. In 1983, the committee was renamed the IAB (Internet Activities Board) and was given a slighter broader mission, namely, to keep the researchers involved with the ARPANET and the Internet pointed more-or-less in the same direction, an activity not unlike herding cats. The meaning of the acronym ''IAB'' was later changed to Internet Architecture Board.
Each of the approximately ten members of the IAB headed a task force on some issue of importance. The IAB met several times a year to discuss results and to give feedback to the DoD and NSF, which were providing most of the funding at this time. When a standard was needed (e.g., a new routing algorithm), the IAB members would thrash it out and then announce the change so the graduate students who were the heart of the software effort could implement it. Communication was done by a series of technical reports called RFCs (Request For Comments). RFCs are stored on-line and can be fetched by anyone interested in them from www.ietf.org/rfc. They are numbered in chronological order of creation. Over 3000 now exist.
By 1989, the Internet had grown so large that this highly informal style no longer worked. Many vendors by then offered TCP/IP products and did not want to change them just because ten researchers had thought of a better idea. In the summer of 1989, the IAB was reorganized again. The researchers were moved to the IRTF (Internet Research Task Force), which was made subsidiary to IAB, along with the IETF (Internet Engineering Task Force). The IAB was repopulated with people representing a broader range of organizations than just the research community. It was initially a self-perpetuating group, with members serving for a 2-year term and new members being appointed by the old ones. Later, the Internet Society was created, populated by people
interested in the Internet. The Internet Society is thus in a sense comparable to ACM or IEEE. It is governed by elected trustees who appoint the IAB members.
The idea of this split was to have the IRTF concentrate on long-term research while the IETF dealt with shortterm engineering issues. The IETF was divided up into working groups, each with a specific problem to solve. The chairmen of these working groups initially met as a steering committee to direct the engineering effort. The working group topics include new applications, user information, OSI integration, routing and addressing, security, network management, and standards. Eventually, so many working groups were formed (more than 70) that they were grouped into areas and the area chairmen met as the steering committee.
In addition, a more formal standardization process was adopted, patterned after ISOs. To become a Proposed Standard, the basic idea must be completely explained in an RFC and have sufficient interest in the community to warrant consideration. To advance to the Draft Standard stage, a working implementation must have been rigorously tested by at least two independent sites for at least 4 months. If the IAB is convinced that the idea is sound and the software works, it can declare the RFC to be an Internet Standard. Some Internet Standards have become DoD standards (MIL-STD), making them mandatory for DoD suppliers. David Clark once made a now- famous remark about Internet standardization consisting of ''rough consensus and running code.''
Metric Units
To avoid any confusion, it is worth stating explicitly that in this book, as in computer science in general, metric units are used instead of traditional English units (the furlong-stone-fortnight system). The principal metric prefixes are listed in Fig. 1-39. The prefixes are typically abbreviated by their first letters, with the units greater than 1 capitalized (KB, MB, etc.). One exception (for historical reasons) is kbps for kilobits/sec. Thus, a 1-Mbps communication line transmits 106 bits/sec and a 100 psec (or 100 ps) clock ticks every 10-10 seconds. Since milli and micro both begin with the letter ''m,'' a choice had to be made. Normally, ''m'' is for milli and ''µ'' (the Greek letter mu) is for micro.It is also worth pointing out that for measuring memory, disk, file, and database sizes, in common industry practice, the units have slightly different meanings. There, kilo means 210 (1024) rather than 103 (1000) because memories are always a power of two. Thus, a 1-KB memory contains 1024 bytes, not 1000 bytes. Similarly, a 1- MB memory contains 220 (1,048,576) bytes, a 1-GB memory contains 230 (1,073,741,824) bytes, and a 1-TB database contains 240 (1,099,511,627,776) bytes. However, a 1-kbps communication line transmits 1000 bits per second and a 10-Mbps LAN runs at 10,000,000 bits/sec because these speeds are not powers of two. Unfortunately, many people tend to mix up these two systems, especially for disk sizes. To avoid ambiguity, in this book, we will use the symbols KB, MB, and GB for 210, 220, and 230 bytes, respectively, and the symbols kbps, Mbps, and Gbps for 103, 106, and 109 bits/sec, respectively.
Network Standardization
4/
5
Oleh
Unknown
