1.2 Determining The WAN Type To Use
1.2.1 Selecting WAN configuration types
When you design networks, you need to make several key decisions concerning connectivity between different users or groups of users in your WAN environment.

When selecting a WAN connection, you should consider the following:

  • Availability -- Each method of connectivity has characteristics inherent in its design, usage, and implementation. For example, Frame Relay is not available in all geographic regions.
  • Bandwidth -- WAN bandwidth is expensive, and organizations cannot afford to pay for more bandwidth than they need. Determining usage over the WAN is a necessary step toward evaluating the most cost-effective WAN services for your needs.
  • Cost -- WAN usage costs are typically 80 percent of the entire Information Services budget. When different WAN services and different service providers are evaluated, cost is a major consideration. If, for example, you use the line for only one hour a day, you may want to select a dial-on-demand connection, such as an asynchronous or ISDN connection.
  • Ease of management -- Network designers are often concerned about the degree of difficulty associated with managing connections. Connection management includes both the configuration at initial startup and the ongoing configuration tasks of normal operation. Traffic management is the capability of the connection to adjust to different rates of traffic, regardless of whether the traffic is steady-state or bursty in nature. Dedicated lines are often easier to manage than shared lines.
  • Application traffic -- The application traffic may be many small packets, such as during a terminal session; or very large packets, such as during file transfer. A dial-on-demand connection may be the best connection type for smaller packets. On the other hand, a packet-switched network may be best for the higher traffic application requirements.
  • Quality of service and reliability -- How critical is the intended traffic for a link? A backup connection may be necessary.
  • Access control -- A dedicated connection may help control access, but e-commerce cannot occur on a wide scale unless consumers access some portion of your network.

The Figure illustrates bandwidth and time-selection considerations (which increase cost) when determining the best WAN technology to use. (The source of the Figure is a 1995 study done by the Forrester Research firm.) The network administrator must determine the best WAN technology to implement based on the amount of bandwidth and the time a user requires on the network. As the time of use increases, WAN services associated with a variable cost, such as dialup, tend to be less advantageous. Likewise, as time of use decreases, WAN services associated with a fixed cost become more advantageous.