Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A network is a communication system that allows users to access resources on other computers and exchange messages with one another. It allows users to share resources on their own system or access shared resources on other systems. Obviously, it is the topic of this entire book, so this section will guide you to the appropriate sections that discuss networking technology. See "Data Communication Concepts" for a similar outline of basic communication concepts.

Before networks, there were centrally controlled mainframe computers built by IBM and other vendors. See "Mainframe" and "SNA (Systems Network Architecture)."

In the late 1960s and early 1970s, a community of researchers started developing the concept of connecting computers together and using packets and packet switches to exchange information. They were creating the early Internet by connecting large mainframes and minicomputers. See "Internet."

In the late 1970s, microcomputer systems began to appear. They soon dominated small offices and workgroups everywhere. It made sense to connect them together so users could communicate with one another and share network resources like printers and disks. The LAN concept took hold in corporations. See "LAN (Local Area Network)." Also refer to the related entries in the LAN section.

Actually, the LAN concept was developed by Robert Metcalfe, who was working with the Internet engineers. He developed the idea after running across a paper describing a satellite communication system called ALOHA at a friend's house. Metcalfe applied the concept to a cabled system and called it Ethernet. Internet engineers loved UNIX and soon connected their systems with Ethernet. In turn, these networks were connected to the Internet via routers.

Meanwhile, LANs (primarily PC and Macintosh LANs) were being installed everywhere. While Ethernet is the dominant LAN technology today, ARCNET had its day and IBM made token ring popular, although it didn't catch on like Ethernet. In the mid-1980s, most LANs were still confined to workgroups and departments. Some organizations connected these LANs to their mainframes and allowed users to exchange e-mail using mainframe e-mail systems. But soon it just made sense to interconnect the entire organization. For a while, this was attempted by joining LANs with bridges, but bridged networks have scalability and security problems. See "Bridges and Bridging."

Fortunately, the Internet engineers had already developed an internetworking device called the router. Routers were developed as gateways devices for the Internet. They interconnect different types of networks while providing a secure barrier between them. This is critical on the Internet, where interconnected networks are autonomous systems operated by different authorities. See "Routers," "Routing," and "Routing on the Internet."

An important feature of routers is that they support an internetwork addressing scheme that assigns a unique address to each individual network that is connected to the internetwork. Routers keep track of these addresses, thus allowing packets to be forwarded from any network to any other network across a mesh of router-connected networks. See "Packets and Packet-Switching Networks."

The TCP/IP protocol suite provides the internetwork addressing scheme and transport scheme for router-connected networks. IP provides the "overlay" addressing scheme and internetwork routing. See "Internetworking," "Internet Protocol Suite," "IP (Internet Protocol)," and "TCP (Transmission Control Protocol)."

Routers were soon appearing in corporate networks to join department and workgroup LANs into enterprise-wide networks. This meant a conversion to TCP/IP protocols. At first there was some resistance, but when the World Wide Web exploded on the scene in the 1990s, no one doubted the advantage of the Internet protocol suite. Web technologies solved an incredible number of hardware and software interoperablitity problems. In fact, the term "interoperability" is rarely heard today because Web technologies minimized the problem.

LAN technologies improved over the years. Ethernet went from 10 Mbits/sec to 100 Mbits/sec (Fast Ethernet) to 1,000 Mbits/sec (Gigabit Ethernet). In addition, switching technologies improved not only performance but the way that networks were designed. See "Network Design and Construction," "Ethernet," "Fast Ethernet," and "Gigabit Ethernet." Switching technologies are discussed under "Switching and Switched Networks."

Another improvement was the multilayer switch, which combined switching and routing into a high-performance hardware-based device that allowed network designers to put routing wherever needed at a relatively inexpensive price in order to segregate networks, provide security, or control traffic. See "Multilayer Switching."

Application development in LAN and internetwork environments was dominated by client/server computing for years, but more recently distributed object computing technologies have prevailed, partly as a result of the Web. The traditional two-tiered client/server model grew into the three-tiered distributed object model. Middleware and messaging technologies simplify the process of connecting applications and processes across global networks. See "Client/Server Computing," "Middleware and Messaging," "DBMS (Database Management System)," "Distributed Applications," "Distributed Object Computing," "Multitiered Architectures," and "Object Technologies."

As mentioned, Web technologies played an important part in redefining access to data, the sharing of data, and the design of network applications. An intranet is an internal network built with Web technologies while an extranet is a business-to-business network with links across the Internet. See "Web Technologies and Concepts" and "Intranets and Extranets."

Recently, core Internet networks have improved with optical switching and the overprovisioning of bandwidth. The last bottleneck is the local access network, which not surprisingly is still controlled to a large extent by the incumbent telephone companies. They require packet-switched network users to adjust to their TDM (time division multiplexing) hierarchy in order to take advantage of metropolitan and wide area network links. These T1, T3, and fractional T1 lines are expensive and inefficient. Fortunately, the access market is changing. In the last few years, competitors have installed fiber-optic cable throughout metropolitan areas and are offering flexible bandwidth options using native protocols (Ethernet) at less than half what the carriers were charging. See "MAN (Metropolitan Area Network)," "Network Access Services," "Network Core Technologies," "TDM Networks," and "WAN (Wide Area Network)."

The final part of this story (at least for this edition) is that the Internet is becoming the network. With fast connections, enterprises are starting to outsource much of their data services to service providers that run Internet data centers. See "ASP (Application Service Providers)," "MSP (Management Service Provider)," and "SSP (Storage Service Provider)." Also see "Outsourcing," These service providers have data centers that are staffed by professionals 24/7 and that provide all the security and high availability to keep an enterprise up and running. See "Data Center Design" and "Fault Tolerance and High Availability."

Outsourcing makes sense because the Internet provides global connections and Internet data centers with direct connections to fast backbones. The cost of equipment and management is shared by all the customers of the service providers. Secure connections can be made across virtual private networks. See "VPN (Virtual Private Network)."

Even users are taking advantage of this scheme. Many are using Web appliances, which are Web-based terminals that rely on Internet applications servers, storage servers, and e-mail servers. All information is stored on the Web. The Internet is essentially becoming a giant storage network. See "Distributed Computer Networks," "NAS (Network Attached Storage)," "Network Appliances," and "Thin Clients."

P2P (peer-to-peer), made famous by Napster community-based file sharing, disrupts the traditional centrally managed storage model. End users host personal collections of music, electronic books, videos, photographs, technical information, software drivers, and so forth on their own computers. P2P software then helps the community of users locate and access files on other user's computers. In this model, end-systems become informal Web storage devices, or what some have called "media collection devices." P2P bypasses the central control that administrators have over information stored on file servers and promotes user-to-user data exchange on the Internet. P2P software features have expanded to support instant messaging, advanced searching, and mailing list support. See "Peer-to-Peer Communications."

A number of other topics are "QoS (Quality of Service)," "Voice/Data Networks," "Mobile Computing," "Security," "Wireless Communications," and "Wireless LANs."