1.3 Identifying Site Requirements and Solutions
1.3.2 Central-site considerations
The central-site WAN connection is a critical focal point for a company. Other sites and users access this site for information. Because many users access this site in a variety of ways, it is important that your central-site solution has a modular design that can accommodate many different types of WAN connections coming in from remote locations, as shown in the Figure.

The technologies and features used to connect company campuses over a WAN are developed to optimize the WAN bandwidth, minimize the cost, and maximize the effective service to end users. You should choose the WAN architecture that provides the most cost-effective bandwidth and a technology that optimizes service to end users. With that in mind, central-site considerations include the following:

  • Multiple access connections -- Multiple users connect to the central site by using different media, so central-site considerations must include multiple media options and simultaneous access from multiple users.
  • Cost -- Keep the costs low while maintaining an adequate level of service. For example, because some WAN charges are based on usage, such as ISDN, it is important that companies have a solution that can implement features that will optimize bandwidth and minimize WAN costs. Features such as DDR and compression ensure that WAN costs are kept to a minimum. In another example, because leased lines are generally charged on a fixed basis, you may want to consider this service only if the line can sustain a certain link-utilization level.
  • Access control -- Company information must be restricted, allowing users access only to areas in the network that they are authorized to access. For example, access lists can filter out unauthorized data flow between offices and PPP network links, whereas Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP) can identify the remote entity to prevent unauthorized network connection.
  • Quality of service -- It is important to prioritize traffic over the link and manage traffic flow so that bursty traffic does not slow mission-critical traffic.
  • Redundancy and backup -- Because a link may fail or high link utilization may occur at certain peak usage times during the day, it is important to back up the connection to the central office. Avoid backing up links using the same service provider.
  • Scalability -- Build a network that will grow with the business.