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This algorithm generates a period of time the network station delays attempting a retransmission; however, the frequency of collisions, jams, and the invocation of backoff algorithms increase as network utilization increases. For an Ethernet LAN, network utilization beyond a 60% level can result in significant degradation of performance, which can serve as a cap on achievable transmission throughput. Thus, the average bandwidth of 400,000 bps previously computed should be multiplied by 60% to obtain a more realistic level of average available bandwidth obtainable by each station on the LAN to include the Web server.
In this example, the Web server will obtain on the average 240,000 bps of LAN bandwidth (i.e., 400,000 bps x .6). Since the average LAN bandwidth obtainable by the Web server exceeds the computed WAN operating rate, no adjustment is required to the LAN. If the Web server was connected to a Token Ring LAN, the average bandwidth of 400,000 bps should be multiplied by 75%, since a Token Ring LAN does not have its performance seriously degraded until network utilization exceeds 75%.
As described thus far, network managers need to consider the LAN bandwidth obtained by the Web server as well as the WAN operating rate to effectively select a wide area network connection method to an IAP. When computing the WAN operating rate, it is important to note that the rate depends on:
The first and third factors are obtained by an estimation process. However, a company has a high degree of control over the composition of its servers Web pages, and this fact can be used as an effective tool in adjusting the WAN connections ability to support the estimated number of hits expected during the busy hour.
Because initial access to a companys Web server is through its home page, that page will have the highest distribution of hits on the company server. Thus, if the estimate of busy hour traffic is low, it is possible to increase the selected WAN operating rate to support additional hits by reducing the transmission associated with each home page hit. Methods include replacing GIF images with their equivalent JPEG images that require less storage, cropping images to reduce their data storage requirements, or eliminating all or some images on the home page.
The selection of an appropriate wide area network operating rate to connect a corporate Web server to the Internet depends on three key factors, of which two the expected number of hits during the busiest hour and the distribution of hits per server page can only be estimated. This means that the WAN operating rates ability to service expected traffic will only be as good as two traffic-related estimates.
However, by planning ahead the organization can adjust the third factor the data storage on the servers home page and obtain the flexibility to alter the selected WAN operating rate to support additional hits during the busy hour.
By following the methodology presented in this chapter, network managers and others involved in corporate Web page creation will be able to remove a large degree of the guesswork associated with connecting a Web server to the Internet. In addition, they should be able to rapidly adjust the capacity of a wide area network connection to support additional Web server hits if such an adjustment should become necessary.
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