Today's network administrators must manage complex wide-area networks (WANs) in order to support the growing number of software applications that are built around Internet Protocol (IP) and the Web. These WANs place a great demand on network resources, and require high-performance networking technologies. WANs are complex environments that incorporate multiple media, multiple protocols, and inter-connection to other networks, such as the Internet. Growth and manageability of these network environments are achieved by the often complex interaction of protocols and features.
Despite improvements in equipment performance and media capabilities, WAN design is becoming more difficult. Carefully designing WANs can reduce problems associated with a growing networking environment. To design reliable, scalable WANs, network designers must keep in mind that each WAN has specific design requirements.
WAN Design Requirements
WAN communication occurs between geographically separated areas. When a local end station wants to communicate with a remote end station (that is, an end station located at a different site), information must be sent over one or more WAN links. Routers within WANs are connection points of a network. These routers determine the most appropriate path through the network for the required data streams.
WAN communication is often called a service because the network provider normally charges users for the WAN services it provides. Circuit-switching and packet-switching technologies are two types of WAN services, each of which has advantages and disadvantages. For example, circuit-switched networks offer users dedicated bandwidth that cannot be infringed upon by other users. In contrast, packet switching is a method in which network devices share a single point-to-point link to transport packets from a source to a destination across a carrier network. Packet-switched networks have traditionally offered more flexibility and used network bandwidth more efficiently than circuit-switched networks.
Traditionally, relatively low throughput, high delay, and high error rates have characterized WAN communication. WAN connections are also characterized by the cost of renting media (wire) from a service provider to connect two or more campuses together. Because the WAN infrastructure is often rented from a service provider, WAN network designs must optimize the cost of bandwidth and bandwidth efficiency. For example, all technologies and features used in WANs are developed to meet the following design requirements: • Optimize WAN bandwidth
• Minimize cost
• Maximize the effective service to the end users
Recently, traditional shared-media networks are being overtaxed because of the following new network requirements: • Network usage has increased as enterprises utilize client/server, multimedia, and other applications to enhance productivity. • The rate of change in application requirements has accelerated and will continue to do so (for example, Internet "push" technologies). • Applications increasingly require distinct network qualities of service due to services they provide end users. • An unprecedented number of connections are being established among offices of all sizes, remote users, mobile users, international sites, customers/suppliers, and the Internet. • The explosive growth of corporate intranets and extranets has created a greater demand for bandwidth. • The increased use of enterprise servers continues to grow to serve the business needs of organizations.
Compared to current WANs, the new WAN infrastructures must be more complex, based on new technologies, and able to handle an ever-increasing (and rapidly changing) application mix with required and guaranteed service levels. In addition, with a 300% traffic increase expected in the next five years, enterprises will feel even greater pressure to contain WAN costs....