Each of the past three centuries has been dominated by a single technology. The 18th century was the time of the great mechanical systems accompanying the Industrial Revolution. The 19th Century was the age of the Steam engine. During the 20th Century, the key technology has been information gathering, processing, and distribution. Among other developments, we have seen the installation of worldwide telephone networks, the invention of radio and television, the birth and unprecedented growth of the computer industry, and the launching of communication satellites.
Due to rapid technological progress, these areas are rapidly converging, and the differences between collecting, transporting, storing, and processing information are quickly disappearing. Organizations with hundreds of offices spread over a wide geographical area routinely expect to be able to examine the current status of even their most remote outpost at the push of a button. As our ability to gather, process, and distribute information grows, the demand for even more sophisticated information processing grows even faster.
The merging of computers and communications hag had a profound influence on the way computer systems are organized. The concept of the “computer center” as a room with a large computer to which users bring their work for processing is now totally obsolete. The old model of a single computer serving all of the organization's computational needs has been replaced by one in which a large number of separate but interconnected computers do the job.These systems are called computer networks.
We will use the term “computer network” to mean an interconnected collection of autonomouscomputers. Two computers are said to being interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, and communication satellites can also be used. By requiring the computer autonomous, we wish to exclude from our definition systems in which there is a clear master/slave relation. If one computer can forcibly start, stop, or control another one, the computers are not autonomous. A system with one control unit and many slaves is not a network; nor is a large computer with remote printers and terminals.
There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, the existence of multiple autonomous computers is transparent (i.e., not visible) to the user. He can type a command to run a program, and it runs. It is up to the operating system to select the best processor, find and transport all the input files to that processor, and put the results in the appropriate place.
In other words, the user of a distributed system is not aware that there are multiple processors; it looks like a virtual uniprocessor. Allocation of jobs to processors and files to disks, movement of files between where they are stored and where they are needed, and all other system functions must be automatic.
With a network, users must explicitly log onto one machine, explicitly submit jobs remotely, explicitly move files around and generally handle all the network management personally. With a distributed system, nothing has to be done explicitly; it is all automatically done by the system without the users' knowledge.
In effect, a distributed system is a software system built on top of a network. The software gives it a high degree of, cohesiveness and transparency. Thus the distinction between a network and a distributed system lies with the software (especially the operating system), rather than with the hardware.
Nevertheless, there is considerable overlap between the two subjects. For example, both distributed systems and computer networks need to move files around. The difference lies in who invokes the movement, the system or the user.
A similar revolution is occurring in telecommunications networks. Technological advances are making it possible for communications links to carry more and faster signals. As a result, services are evolving to allow use of the expanded capacity, including extensions to established telephone services such as conference calling, call waiting, voice mail, and caller ID; new digital services include video conferences and information retrieval.
A network is a set of devices (often referred to as nodes) connected by media links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. The links connecting the devices are often called communication channels.
Computer networks have become an indispensable part of business, industry and enter-
tainment in the short time they have been around. Some of the network applications in different fields are as follows.
· Marketing and sales: Computer networks are used extensively in both marketing and sales organizations. Marketing professionals use them to collect, exchange and analyze data relating to customer needs and product development cycles. Sales applications include teleshopping, which use order-entry computer or telephones connected to an order-processing network, on-line reservation services for hotels, airlines, and so on.
· Manufacturing: Computer networks are used today in many aspects of manufacturing, including the manufacturing process itself. Two applications that use networks to provide essential services are computer-assisted design (CAD) and computer-assisted manufacturing (CAM), both of which allow multiple users to work on a project simultaneously.
· Electronic messaging: Probably the most widely used network application is electronic mail (e-mail).
· Directory services: Directory services allow lists of files to be stored in a central locationto speed worldwide search operations.
· Information services: Network information services include bulletin boards and data banks. A World Wide Web site offering the technical specifications for a new product is an information service.
· Electronic data interchange (EDI): EDI allows business information (including docu-
ments such as purchase orders, and invoices) to be transferred without using paper.
· Teleconferencing: Teleconferencing allows conferences to occur without the participants being in the same place. Applications include simple text conferencing (where participants communicate through their keyboards and computer monitors), voice conferencing (where participants at a number of locations communicate simultaneously over the phone), and video conferencing (where participants can see as talk to one another).
· Cellular telephone: In the past, two parties wishing to use the services of the telephone company had to be linked by a fixed physical connection. Today's cellular networks make it possible to maintain wireless phone connections even while traveling over large distances.
· Cable television: Future services provided by cable television networks may include video on request, as well as the same information, financial, and communications services currently provided by the telephone companies and computer networks.
There is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: transmission technology and scale. We will now examine each of these in turn.
Broadly speaking, there are two types of transmission technology:
· Broadcast networks.
· Point-to-point networks.
Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets in certain contexts, sent by one machine are received by all the others. An address field within the packet specifies for whom it is intended. Upon receiving a packet, a machine checks the address field. If the packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignored.
Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting—Some broadcast systems also support transmission to a subset of the machines, something known as multicasting. One possible scheme is to reserve one bit to indicate multicasting. The remaining n –1 address bits can hold a group number. Each machine can “subscribe” to any or all of the groups. When a packet is sent to a certain group, it is delivered to all machines subscribing to that group.
In contrast, point-to-point networks consist of many connections between individual pairs of machines. To go from the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often multiple routes of different lengths are possible, so routing algorithms play an important role in point-to-point networks. As a general rule (although there are many exceptions), smaller, geographically localized networks tend to use broadcasting, whereas larger networks usually are point-to-point.
An alternative criterion for classifying networks is their scale. They can be divided into local, metropolitan, and wide area networks by their physical size. Finally, the connection of two or more networks is called an internetwork. The worldwide Internet is a well-known example of an internetwork.
（1）Local Area Networks.
Local area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in size. They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information. LANs are distinguished from other kinds of networks by three characteristics: their size, their transmission technology, and their topology.
LANs often use a transmission technology consisting of a single cable to which all the machines are attached. Traditional LANs run at speeds of 10 or 100 Mbps, have low delay (tens of microseconds), and make very few errors. Today, however, speeds are increasing and can reach hundreds of megabits/sec with gigabit systems in development.
In general, a given LAN will use only one type of transmission medium. Various topology are possible for LANs. The most common LAN topologies are bus, ring and star.
（2）Metropolitan Area Networks.
A metropolitan area network, or MAN (plural: MANs, not MEN) is basically a bigger version of a LAN and normally uses similar technology. It might cover a group of nearby corporate offices or a city and might be either private or public. A MAN can support both data and voice, and might even be related to the local cable television network.
MAN is designed to extend over an entire city. It may be a single network such as a cable television network, or it may be a means of connecting a number of LANs into a larger network so that resources may be shared LAN-to-LAN as well as device-to-device. For example, a company can use a MAN to connect the LANs in all of its offices throughout a city.
（3）Wide Area Networks.
A wide area network, or WAN, spans a large geographical area that may comprise a country, a continent, or even the whole world. It provides long-distance transmission of data, voice, image, and video information over large geographical areas.
In contrast to LANs (which depend on their own hardware for transmission), WANs may utilize public, leased, or private communication devices, usually in combinations, and can therefore span an unlimited number of miles.
A WAN that is wholly owned and used by a single company is often referred to as an enterprise network.
（4）Internetworks.
Many networks exist in the world, often with different hardware and software. People connected to one network often want to communicate with people attached to a different one. This desire requires connecting together different, and frequently incompatible networks, sometimes by using machines called gateways to make the connection and provide the necessary translation, both in terms of hardware and software. A collection of interconnected networks is called an internetwork or just internet.
When two or more networks are connected, they become an internetwork. Individual networks are joined into internetworks by the use of internetworking devices. These devices include routers and gateways. The term internet (lowercase i) should not be confused with the Internet (uppercase I). The first is a generic term used to mean an interconnection of networks. The second is the name of a specific worldwide network.
Many network vendors and suppliers exist, each with their own ideas of how things should be done. Without coordination, there would be complete chaos, and users would be able to get nothing done. The only way out is to agree upon some network standards.
Standards fall into two categories: de facto (meaning “by fact” or “by convention”) and de jure (meaning “by law” or “by regulation”).
De jure standards are those that have been legislated by an officially recognized body. Standards that have not been approved by an organized body but have been adopted as standards through widespread use are de facto standards. De facto standards are often established originally by manufacturers seeking to define the functionality of a new product, or technology.
Many organizations are dedicated to the establishment of standards. The primary standards organizations are the following:
（1）ISO.
The International Standards Organization (ISO) is an international agency founded in 1946 for the development of standards on a wide range of subjects. It is a voluntary, non-treaty organization whose members are designated standards bodies of participating nations, plus nonvoting observer organizations. Although ISO is not a governmental body, more than 70 percent of ISO member bodies are governmental standards institutions or organizations incorporated by public law. Most of the remainders have close links with the public administration in their own countries. The United States is represented in the ISO by ANSI (American National Standard Institute).
ISO has issued more than 5000 standards in a broad range of areas. Its purpose is to promote the development of standardization and related activities to facilitate international exchange of goods and services and to develop cooperation in the sphere of intellectual, scientific, technological, and economic activity. Standards have been issued to cover everything from screw threads to solar energy. One important area of standardization deals with the open systems interconnection (OSI) communications architecture and the standards at each layer of the OSI architecture.
（2）ITU-T.
The ITU Telecommunications Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union (ITU), which is itself a United National specialized agency. Hence, the members of ITU-T are governments. The U.S. representation is housed in the Department of State. The charter of the ITU is that it “is responsible for studying technical, operating, and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis”. Its primary objective is to standardize, to the extent necessary, techniques and operations in telecommunications to achieve end-to-end compatibility of international telecommunication connections regardless of the countries of origin and destination.
The ITU-T was created on March 1, 1993, as one consequence of a reform process within the ITU. It replaces the International Telegraph and Telephone Consultative Committee (CCITT), which had essentially the same chart and objectives as the new ITU-T.
（3）ANSI.
Despite its name, the American National Standards Institute (ANSI) is a completely private nonprofit corporation not affiliated with the U.S. federal government. However, all ANSI activities are undertaken with the welfare of the United States and its citizen occupying primary importance ANSI's expressed aims include serving as the national coordinating institution for voluntary standardization in the United States, furthering the adoption of standards as a way of advancing the U.S. economy, and ensuring the participation and protection of the public interests. ANSI members include manufacturers, common carriers, and other interested parties. Current areas of discussion include internetwork planning and engineering; ISDN services, signaling, and architecture; and optical hierarchy (SONET).
ANSI submits proposals to the ITU-T and is the designated voting member from the United States to the ISO. The Committee of European Post, Telegraph, and Telephone (CEPT) and the European Telecommunications Standards Institute (ETSI) provide similar services in the European Community.
ANSI is the U.S. voting representative to both the ISO and the ITU-T.
（4）IEEE.
The Institute of Electrical and Electronics Engineers (IEEE) is the largest professional engineering society in the world. International in scope, it aims to advance theory, creativity, and product quality in the fields of electrical engineering, electronics, and radio as well as in all related branches of engineering. As one of its goals, the IEEE oversees the development and adoption of international standards for computing and communication. The IEEE has a special committee for local area networks (LANs), out of which has come Project 802 (e.g., the 802.3, 802.4, and 802.5 standards).
1s and 0s cannot be sent as such across network links. They must be further converted into a form that transmission media can accept. Transmission media work by conducting energy along a physical path. So, a data stream of 1s and 0s must be turned into energy in the form of electromagnetic signals.
（1）Analog and Digital.
Both data and the signals that represent them can take either analog or digital form. Analog refers to something that is continuous—a set of specific points of data and all possible point between. Digital refers to something that is discrete.
Information can be analog or digital. Analog information is continuous. Digital information is discrete.
Signals can be analog or digital. Analog signals can have any value in a range; digital signals can have only a limited number of values.
（2）Frequency, Spectrum and Bandwidth.
The electromagnetic signal is a function of time, but it can also be expressed as a function of frequency; that is, the signal consists of components of different frequencies.
The spectrum of a signal is the range of frequencies that is contained. The absolute bandwidth of a signal is the width of the spectrum. Many signals have an infinite bandwidth. However, most of the energy in the signal is contained in a relatively narrow band of frequencies. This band is referred to as the effective bandwidth, or just bandwidth.
（3）Bit Rate and Baud Rate.
Two terms used frequently in data communication are bit rate and baud rate. Bit rate is the number of bits transmitted during one second. Baud rate refers to the number of signals units per second that are required to represent those bits.
How information is encoded depends on its original format and on the format used by the communication hardware.
As is known, information can be of two types, digital or analog, and signals can be of two types, also digital or analog. Therefore, four types of encoding are possible: digital-to-digital, analog-to-digital, digital-to-analog, and analog-to-analog.
· Digital-to-digital encoding is the representation of digital information by a digital signal.
· Analog-to-digital encoding is the representation of analog information by a digital signal.
· Digital-to-analog encoding is the representation of digital information by an analog signal.
· Analog-to-analog encoding is the representation of analog information by an analog signal. Radio, that familiar utility, is an example of an analog-to-analog.
The term transmission mode is used to define the direction of signal flow between two linked devices. There are three types of transmission modes: simplex, half-duplex, and full-duplex.
（1）Simplex.
In simplex mode, the communication is unidirectional, as one one-way street. Only one of the two stations on a link can transmit; the other can only receive.
Keyboards and traditional monitors are both examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output.
（2）Half-Duplex.
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.
In a half-duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time. Walkie-talkies and CB radios are both half-duplex systems.
（3）Full-Duplex.
In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously.
The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time. In full-duplex mode, signals going in either direction share the capacity of the link. This sharing can occur in two ways: either the link must contain two physically separate transmission paths, one for sending, the other for receiving, or the capacity of the channel is divided between signals traveling in opposite directions.
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computer networks |
计算机网络 |
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distributed system |
分布式系统 |
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network |
网络 |
|
Electronic Data Interchange (EDI) |
电子数据交换 |
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teleconferencing |
电信会议 |
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broadcast networks |
广播式网络 |
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point-to-point networks |
点到点网络 |
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Local Area Networks (LANs) |
局域网 |
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Metropolitan Area Networks (MANs) |
城域网 |
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Wide Area Networks (WANs) |
广域网 |
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internetwork |
互联网 |
|
ISO (International Standards Organization) |
国际标准化组织 |
|
ITU-T (International Telecommunications Union) |
国际电信联盟电信标准化部 |
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ANSI (American National Standards Institute) |
美国国家标准协会 |
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baud rate |
波特率 |
|
simplex |
单工 |
|
Half-duplex |
半双工 |
|
Full-duplex |
全双工 |
（1）computer networks（计算机网络）。计算机网络就是把分布在不同地点的、具有独立功能的多个计算机物理地连接起来，按照网络协议相互通信，以共享软件、硬件和数据资源为目标的系统。
（2）distributed system（分布式系统）。分布式系统是建立在网络之上的软件系统，它具有高度的整体性和透明性。
（3）electronic data interchange（EDI，电子数据交换）。一种电子传输方法，使用这种方法，首先将商业或行政事务处理中的报文数据按照一个公认的标准，形成结构化的事务处理的报文数据格式，进而将这些结构化的报文数据经过网络，从计算机传输到计算机。
（4）Teleconferencing（电信会议）。通过使用电信设备（例如闭路电视）而使位于不同地点的人召开的会议。
（5）Local Area Networks（LAN，局域网）。一种连接办公室电子设备并在一间办公室或一座建筑物内构成一个网络的系统。
（6）Metropolitan Area Networks（MAN，城域网）。在5km～10km的地理覆盖范围内，以较高的传输速率充分支持数据、声音和图像综合业务传输的一种通信网络。
（7）Wide Area Networks（WAN，广域网）。也称远程网，它作用的地理范围从数十公里到数千公里，可以连接若干个城市、地区，甚至跨国界，遍及全球的一种通信网络。
（8）internetwork（互联网）。是指将分布在不同地理位置的网络、设备相连接，以构成更大规模的互联网络系统，实现互联网络的共享。
（9）bandwidth（带宽）。通信频带宽度，简称带宽。是指信道上能够传输信号的最大频率范围。
（10）bit rate（比特率，位速率）。二进制数据在一条通信线路上的传输速度，通常用每秒多少位（bps）来表示。
（11）baud rate（波特率）。每秒钟能够传送信息位的数量，是所传送的代码的最短码元占有时间的倒数。
（12）simplex（单工）。信号只能按一个方向传播，任何时候都不能改变信号的传播方向，如电视信号。
（13）half-duplex（半双工）。信号可以双向传送，但必须交替进行，一个时间只能向一个方向传送，如电话线路。
（14）full-duplex（全双工）。信号可以同时双向传送，例如计算机之间的通信。
1. Fill in the following blanks.
（1）A is a set of devices (often referred to as nodes) connected by media links. A node can be a computer, printer, or any other device capable of sending and/or receiving data.
（2） allows conferences to occur without the participants being in the same place. Applications include simple conferencing (where participants communicate through their keyboards and computer monitors), conferencing (where participants at a number of locations communicate simultaneously over the phone), and
conferencing (where participants can see as talk to one another).
（3）There are two types of transmission technology: and .
（4）Networks can be divided into , , and by their scale.
（5）The connection of two or more networks is called an .
（6） is the number of bits transmitted during one second. refers to the number of signal units per second that are required to represent those bits.
2. Single choice.
（1） spans a large geographical area that may comprise a country, a continent, or even the whole world. It provides long-distance transmission of data, voice, image, and video information over large geographical areas.
A. LAN B. MAN C. WAN D. Internetwork
（2）The standardization of the Open Systems Interconnection (OSI) communications architecture and the standards at each layer of the OSI architecture are developed by .
A. IEEE B. ANSI C. ISO D. ITU-T
3. List four primary network standards organizations.
DEEP WEB
Most writers these days do a significant part of their research using the World Wide Web, with the help of powerful search engines such as Google and Yahoo. There is so much information available that one could be forgiven for thinking that “everything” is accessible this way, but nothing could be further from the truth. For example, as of August 2005, Google claimed to have indexed 8.2 billion Web pages and 2.1 billion images. That sounds impressive, but it's just the tip of the iceberg. Behold the deep Web.
According to Mike Bergman, chief technology officer at BrightPlanet Corp., more than 500 times as much information as traditional search engines “know about” is available in the deep Web. This massive store of information is locked up inside databases from which Web pages are generated in response to specific queries. Although these dynamic pages have a unique URL address with which they can be retrieved again, they are not persistent or stored as static pages, nor are there links to them from other pages.
The deep Web also includes sites that require registration or otherwise restrict access to their pages, prohibiting search engines from browsing them and creating cached copies.
Let's recap how conventional search engines create their databases. Programs called spiders or Web crawlers start by reading pages from a starting list of Web sites. These spiders first read each page on a site, index all their content and add the words they find to the search engine's growing database. When a spider finds a hyperlink to another page, it adds that new link to the list of pages to be indexed. In time, the program reaches all linked pages, presuming that the search engine doesn't run out of time or storage space. These linked pages constitute what most of us use and refer to as the Internet or the Web. In fact, we have only scratched the surface, which is why this realm of information is often called the surface Web.
Why don't our search engines find the deeper information? For starters, let's consider a typical data store that an individual or enterprise has collected, containing books, texts, articles, images, laboratory results and various other kinds of data in diverse formats. Typically we access such database information by means of a query or search.
We type in the subject or keyword we're looking for, the database retrieves the appropriate content, and we are shown a page of results to our query.
If we can do this easily, why can't a search engine? We assume that the search engine can reach the query input (or search) page, and it will capture the text on that page and in any pages that may have static hyperlinks to it. But unlike the typical human user, the spider can't know what words it should type into the query field. Clearly, it can't type in every word it knows about, and it doesn't know what's relevant to that particular site or database. If there's no easy way to query, the underlying data remains invisible to the search engine. Indeed, any pages that are not eventually connected by links from pages in a spider's initial list will be invisible and thus are not part of the surface Web as that spider defines it.
According to a 2001 BrightPlanet study, the deep Web is very big indeed: The company found that the 60 largest deep Web sources contained 84 billion pages of content with about 750TB of information. These 60 sources constituted a resource 40 times larger than the surface Web. Today, BrightPlanet reckons the deep Web totals 7500TB, with more than 250,000 sites and 500 billion individual documents. And that's just for Web sites in English or European character sets. (For comparison, remember that Google, the largest crawler-based search engine, now indexes some 8 billion pages.)
The deep Web is getting deeper and bigger all the time. Two factors seem to account for this. First, newer data sources (especially those not in English) tend to be of the dynamic- query/searchable type, which are generally more useful than static pages. Second, governments at all levels around the world have made commitments to making their official documents and records available on the Web.
Interestingly, deep Web sites appear to receive 50 percent more monthly traffic than surface sites do, and they have more sites linked to them, even though they are not really known to the public. They are typically narrower in scope but likely to have deeper, more detailed content.
ABOUT INTERNET 2
（1）What is Internet 2?
Internet 2 is a not-for-profit consortium, led by over 180 US universities, developing and deploying advanced network applications and technology, accelerating the creation of tomo-
rrow's Internet. With participation by over 60 leading companies, Internet 2 recreates the partnership of academia, industry and government that helped foster today's Internet in its infancy.
（2）Is Internet 2 a separate network? Will Internet 2 replace the current commercial Internet?
Internet 2 is not a separate physical network and will not replace the Internet. Internet 2 brings together institutions and resources from academia, industry and government to develop new technologies and capabilities that can then be deployed in the global Internet. Close collaboration with Internet 2 corporate members will ensure that new applications and technologies are rapidly deployed throughout the Internet. Just as E-mail and the World Wide Web are legacies of earlier investments in academic and federal research networks, the legacy of Internet 2 will be to expand the possibilities of the broader Internet.
（3）How will Internet 2 benefit current Internet users?
Internet 2 and its members are developing and testing new technologies, such as IPV6, multicasting, and QoS. However, these applications require performance not possible on today's Internet. More than a faster Web or E-mail, these new technologies will enable completely new applications such as digital libraries, virtual laboratories. Distance-independent learning and tele-immersion. A primary goal of Internet 2 is to ensure the transfer of new network technology and applications to the broader education and networking communities.
（4）What is the relationship between the Next Generation Internet (NGI) Internet 2, and other advanced networking initiatives?
The university-led Internet 2 and the federally-led NGI are parallel and complementary initiatives based in the United States. Internet 2 and NGI are already working together in many areas. For example, through participation in a NSF NGI program, over 150 Internet 2 universities have received competitively awarded grants to support connections to advanced backbone networks such as Abilene and the very high performance Backbone network service (vBNS). Internet 2 is also forming partnerships with similar advanced networking initiatives around the world. Working together will help ensure a cohesive and interoperable advanced networking infrastructure for research and education, and the continued interoperability of the global Internet.
（5）What are some of Internet 2's long-term goals?
A key goal of this efforts is to accelerate the diffusion of advanced Internet technology, in particular into the commercial sector. In this way, Internet 2 will help to sustain United States leadership in internetworking technology. Internet 2 will benefit non-university members of the educational community as well, especially k-12 and public libraries. Internet 2 and its members aim to share their expertise with as wide arrange of computer users as possible. This approach characterized the first Internet and it can work again today. For Internet 2 universities, this means providing high-performance networking on their campuses-investing to upgrade their campus networks and connecting to a national Internet 2 backbone network. For Internet 2 corporate partners, this means actively collaborating with Internet 2 universities and in Internet 2 initiatives.
NETWORKING IN WindowsNT
As a sample of typical LAN we delineate here the architecture of networking in Windows NT, enabling you to visualize the flow of data from the application to the network through Windows NT networking components.
At the physical layer, Windows NT provides suitable MAC drivers for most networking media such as Ethernet, Token Ring, and FDDI. It also supports remote (that is, telephone) Windows NT server access from a Windows NT workstation. To do this, it uses the telephone network with a built-in facility known as remote access service (RAS). The upper layers through the Network Driver Interface Specification (NDIS) 3.0 can access all the MAC drivers in a Windows NT environment. Windows NT provides drivers for most industry standard protocols, such as NetBEUI, NWLink, (the Microsoft-supplied IPX/SPX-compatible protocol stack), TCP/IP, AppleTalk, OSI/TP, and DECNet. Windows NT provides built-in drivers, called the redirector and the server, so users can access or share network resources, respectively. The redirector and the file server communicate with each other using the server message block (SMB) protocol.
In Windows and Windows NT environments, a special set of APIs are available for accessing the network resources (for example, storage, printers) made available by file servers and print servers. These interfaces, called WinNet APIs or WNet APIs, are available on Windows NT as part of the Win32 API set. In the Windows environment, the WinNet APIs are a subset of the Win32 WinNet APIs.
The most important feature of these APIs is that they can be used to access network resources regardless of the type of the underlying network software. For example, a WinNet API used to browse the servers present on the network will function properly whether the workstation is using a Windows NT network or a Novell NetWare network.
For system administrators to have tight control over user access, Windows NT uses domains. Each domain is an environment comprising computers, users, and resources in which one Windows NT server is designated as the domain controller (DC). A domain can have an almost unlimited number of Windows NT servers, Windows NT workstations, Windows workstations (including Windows for Workgroups), and users.
In the domain model, an administrator controls access to all the servers with that one DC, which validates each user's logon and access rights to all resources in the domain. Each user has a single account for the entire domain. This account is maintained on the DC. This contrasts with some network systems in which a user has an account for each server. In such systems, the administrator must manage user accounts on each individual server. The single account in a domain allows the administrator to manipulate user access by manipulating user account attributes.
Windows NT provides four built-in security features: secure logon facility, discretionary access control, auditing, and memory protection.
Windows NT Server, as its name implies, is a server operating system. It is optimized to provide network services to client computers. Although Windows NT Server could be used as a client operating system, Windows NT Workstation is more suited to that task because it costs less. Windows NT Server is at home in the center of your network providing file and print services, routing mail and other network traffic, and supporting back-end software such as database servers and Internet host packages.
The Windows NT Server is a large and complex operating system with many modular components. However, three major constituents—the operating system kernel, the file system, and the networking services—interact to provide Windows NT Server's characteristic features and capabilities as a network server.
Windows NT Server may look like Windows 95, but in actuality it is completely different internally. Although Windows 95 can trace its genealogy all the way back to the first versions of MS-DOS, Microsoft wrote the Windows NT operating system from scratch in the late 1980s. This fresh beginning allowed the developers of Windows NT to take advantage of such developments in operating systems and computer hardware as preemptive multitasking, multiprocessing, multi-platform support, secure file systems, and fault tolerance.