2.2-11a. Local Web Caching (a). Consider the following scenario, in which a Web browser (lower) connects to a web server (above). There is also a local web cache in the bowser’s access network. In this question, we will ignore browser caching (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time propagation, queueing and object transmission delay between the browser and web server (and including TCP setup time) is 250 msec; if the object is retrieved from the local web cache, this delay is only 10 msec.Suppose that 80 percent of the time when the browser makes a request, the requested object is found in the local web cache. What is the average time (over all requests that the browser makes to this site) from when the browser issues the initial HTTP GET request until it is able to display the requested object?Group of answer choices250 msec220 msec420 msec230 msec58 msec88 msec120 msec
Question
2.2-11a. Local Web Caching (a). Consider the following scenario, in which a Web browser (lower) connects to a web server (above). There is also a local web cache in the bowser’s access network. In this question, we will ignore browser caching (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time propagation, queueing and object transmission delay between the browser and web server (and including TCP setup time) is 250 msec; if the object is retrieved from the local web cache, this delay is only 10 msec.Suppose that 80 percent of the time when the browser makes a request, the requested object is found in the local web cache. What is the average time (over all requests that the browser makes to this site) from when the browser issues the initial HTTP GET request until it is able to display the requested object?Group of answer choices250 msec220 msec420 msec230 msec58 msec88 msec120 msec
Solution
To calculate the average time from when the browser issues the initial HTTP GET request until it is able to display the requested object, we need to consider both scenarios: when the object is in the local web cache and when it is not.
- When the object is in the local web cache (which happens 80% of the time), the delay is 10 msec.
- When the object is not in the local web cache (which happens 20% of the time), the delay is 250 msec.
We can calculate the average time as follows:
(0.80 * 10 msec) + (0.20 * 250 msec) = 8 msec + 50 msec = 58 msec
So, the average time from when the browser issues the initial HTTP GET request until it is able to display the requested object is 58 msec.
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