| A | B |
|---|
| WAN design requirements | 1) Optimize WAN bandwidth; 2) Minimize cost; 3) Maximize the effective service to the end users |
| 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. |
| Two primary goals drive WAN design and implementation | Application availability & Total cost of ownership |
| Application availability | Networks carry application information between computers. If the applications are not available to network users, the network is not doing its job. |
| Total cost of ownership | Information Systems (IS) department budgets often run in the millions of dollars. As large businesses increasingly rely on electronic data for managing business activities, the associated costs of computing resources will continue to rise. A well-designed WAN can help to balance these objectives. When properly implemented, the WAN infrastructure can optimize application availability and allow the cost-effective use of existing network resources. |
| WAN design needs to take into account three general factors | Environmental variables; Performance constraints;Networking variables |
| Environmental variables | Environmental variables include the location of hosts, servers, terminals, and other end nodes; the projected traffic for the environment; and the projected costs for delivering different service levels. |
| Performance constraints | Performance constraints consist of network reliability, traffic throughput, and host/client computer speeds (for example, network interface cards and hard drive access speeds). |
| Networking variables | Networking variables include the network topology, line capacities, and packet traffic. |
| The chief components of application availability | response time, throughput, and reliability: |
| Response time | the time between entry of a command or keystroke and the host system's execution of the command or delivery of a response. Applications in which fast response time is considered critical include interactive online services, such as automated tellers and point-of-sale machines. |
| Throughput-intensive applications | generally involve file-transfer activities. However, throughput-intensive applications also usually have low response-time requirements. Indeed, they can often be scheduled at times when response-time-sensitive traffic is low (for example, after normal work hours). |
| reliability | Although reliability is always important, some applications have genuine requirements that exceed typical needs. Organizations that conduct all business activities online or over the telephone require nearly 100% uptime. Financial services, securities exchanges, and emergency, police, and military operations are a few examples. These situations require a high level of hardware and redundancy. Determining the cost of downtime is essential in determining the importance of reliability to your network |
| assess user requirements | User community profiles; Interviews, focus groups, and surveys; interviews with key user groups; Human factors tests |
| User community profiles | Outline what different user groups require. This is the first step in determining network requirements. Although most general users have the same requirements of e-mail, they may also have different needs such as sharing local print servers in their area. |
| Interviews, focus groups, and surveys | build a baseline for implementing a network. Understand that some groups might require access to common servers. Others might want to allow external access to specific internal computing resources. Certain organizations might require IS support systems to be managed in a particular way, according to some external standard. |
| interviews with key user groups | The least formal method of obtaining information is to conduct interviews with key user groups. Focus groups can also be used to gather information and generate discussion among different organizations with similar (or dissimilar) interests. Finally, formal surveys can be used to get a statistically valid reading of user sentiment regarding a particular service level. |
| Human factors tests | The most expensive, time-consuming, and possibly revealing method of assessing user requirements is to conduct a test involving representative users in a lab environment. This is most applicable when you're evaluating response time requirements. For example, you might set up working systems and have users perform normal remote host activities from the lab network. By evaluating user reactions to variations in host responsiveness, you can create benchmark thresholds for acceptable performance. |
