Network engineers and application developers can use several techniques to improve the response time for HTTP requests. a. Explain how using the conditional GET method and web caching can improve the response time for HTTP requests.

b. * To emphasize the importance of web caching, consider the following scenario: An institutional network runs over a LAN with RLAN = 100 Mbps, that has several hosts acting primarily as HTTP clients. The gateway router of the institution is connected to the ISP router, in the public Internet, by a DSL link with Racc = 10 Mbps. The origin HTTP servers, also attached to the Internet, have web objects e.g. HTML, JPG, MPEG files that are requested by the clients. Suppose that the average request size is Lreq = 1 kilobits, the average object size is Lobj = 1 megabits, and that the average request rate from the HTTP clients to the origin servers is = 10 req./s. Assume the average round-trip Internet delay is Tint = 1 s. As a rough approximation, if the traffic intensity on a given link is < 0.8 then the incurred delay is negligible. Otherwise, the link delay must be accounted for in the overall total delay.

i. For a given request (including its returned object), what is the expected internal LAN round-trip delay, TLAN, assuming that propagation and processing delays are negligible inside the LAN?

ii. Without web caching, what is the total response time T0, i.e. the time from the browsers request of an object until its receipt of the object?

iii. With web caching, assuming an average cache hit rate = 0.9, what is the new total response time T1?