Network design is a category of systems design that deals with data transport mechanisms. As with other systems' design disciplines, network design follows an analysis stage, where requirements are generated, and precedes implementation, where the system (or relevant system component) is constructed. The objective of network design is to satisfy data communication requirements while minimizing expense. Requirement scope can vary widely from one network design project to another based on geographic particularities and the nature of the data requiring transport.
Network analysis may be conducted at an inter-organizational, organizational, or departmental level. The requirements generated during the analysis may therefore define an inter-network connecting two or more organizations, an enterprise network that connects the departments of a single organization, or a departmental network to be designed around specific divisional needs. Inter-networks and enterprise networks often span multiple buildings, some of which may be hundreds or thousands of miles apart. The distance between physical connections often dictates the type of technology that must be used to facilitate data transmission.
Components that exist within close physical proximity (usually within the same building) and can be connected to each other directly or through hubs or switches using owned equipment are considered part of a local area network (LAN) . It is generally impractical and often impossible to connect the equipment of multiple buildings as a single LAN; so individual LANs are instead interconnected to form a greater network, such as a metropolitan area network (MAN) or wide area network (WAN).
MANs may be constructed where buildings are located close enough to each other to facilitate a reliable high-speed connection (usually less than 50 kilometers or 30 miles). Greater distances generally result in much slower connections, which are often leased from common carriers to create WANs. Due to the close proximity of equipment, LAN connections offer the best performance and control (usually with speeds around 100 Mbps) and WAN connections the worst (with many machines often sharing a single connection of less than 2 Mbps).
Networks connect machines—which may be computers, computer peripherals, digital telephones, or other digital communication equipment— to each other for the purpose of exchanging data. The data carried by a network may represent voice, video, text, numeric values, or computer-readable code. Regardless of its context at the machines that send and receive the data, the data are handled by the physical network as an uninterpreted series of Boolean values or binary digits called a bitstream . At this lowest logical level, these values of zero and one are represented on the physical network as discrete electronic pulses (baseband) or frequency modulations (broadband) depending on the physical transmission method chosen for a given network segment.
The physical network is responsible for delivering the bitstream to its destination without regard to the high-level meaning of the data. In this sense, all computer networks are responsible for performing the same function. Because the bitstream must include data from many different machines, however, the network needs to define a method for sharing the physical resources. This method, referred to as network architecture, determines the means by which data from competing machines are introduced to the network and delivered to the appropriate destinations.
Common network architectures for LANs and MANs, also called Media Access Control (MAC) protocols, include Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), and Asynchronous Transfer Mode (ATM). Most network architectures dictate specific physical topologies, including the type of medium to be used and its configuration. Token passing methods, such as FDDI and Token Ring for instance, require physical rings of a specified cable. The various MAC protocols and physical mediums—including copper wire, glass fiber, and radio frequency—all possess relative advantages and limitations in terms of speed, consistency, security, expense, and many other important attributes. The combination of these characteristics means that, although all networks can carry all varieties of data, some network architectures are better suited for certain types of data than others. A primary planning function in network design is the determination of which network architecture best suits the type of data the network is being built to support.
Using inter-networking protocols, such as TCP/IP, MANs, and WANs, one can connect many local area networks incorporating a variety of different LAN architectures. This capability affords the network designer some flexibility to choose MAC protocols that best accommodate the needs of a given network segment without jeopardizing connectivity to the rest of the enterprise or inter-organizational network.
A network planning effort, therefore, may conclude that a segment with requirements focused around multimedia use ATM for its consistent performance, while another segment of the same enterprise network with less demanding performance requirements use Ethernet for its low cost and compatibility with existing hardware. Such network segments are interconnected using routers , which strip MAC-specific addressing from data packages, or packets, and rebuild the addresses at the destination segment using the appropriate MAC protocol.
So although many different MAC configurations can interconnect seamlessly, a common inter-networking protocol must be chosen and adhered to across the network in order to realize data communication between all machines. Increasingly, and especially for organizations wanting to connect to the public Internet, that choice is TCP/IP.
Network design is an ongoing effort at most organizations because new applications and business growth create new requirements, which can be fulfilled with ever improving network technology. Network engineering, of which network design is a component, is a balance between performance and expense. So as communication technology continues to improve, resulting in higher data speeds and lower costs, network analysis and redesign is continually necessary to maintain that balance effectively.
see also Internet; Network Protocols; Network Topologies; Security; Telecommunications.
Jeffrey C. Wingard
Goldman, James E. Applied Data Communications: A Business Oriented Approach. New York: John Wiley & Sons, 1995.
Stamper, David A. Business Data Communications. Redwood City, CA: Benjamin/Cummings Publishing Company, 1989.