Just as application requirements drive the Enterprise Campus design , they also affect the Enterprise Edge WAN design. Application availability is a key user requirement; the chief components of application availability are response time, throughput, packet loss, and reliability.

Response Time

Response time is the time between a user request (such as the entry of a command or keystroke) and the host system’s command execution or response delivery. Users accept response times up to some limit, at which point user satisfaction declines. Applications for which fast response time is considered critical include interactive online services, such as point-of-sale machines.

Throughput

In data transmission, throughput is the amount of data moved successfully from one place to another in a given time period. Applications that put high-volume traffic onto the network have more effect on throughput than interactive end-to-end connections. Throughput-intensive applications typically involve filetransfer activities that usually have low response-time requirements and can often be scheduled at times when response-time-sensitive traffic is low (such as after normal work hours). This could be accomplished via time-based access lists, for example.

Packet Loss

In telecommunication transmission, packet loss is expressed as a bit error rate (BER), which is the percentage of bits that have errors, relative to the total number of bits received in a transmission.

Reliability

Although reliability is always important, some applications have requirements that exceed typical needs. Financial services, securities exchanges, and emergency, police, and military operations areexamples of organizations that require nearly 100 percent uptime for critical applications. These situations imply a requirement for a high level of hardware and topological redundancy. Determining the cost of any downtime is essential for determining the relative importance of the network’s reliability.