Consider the figure above where users in an institutional network need to download a web page from a remote web server, with an average rate of 5 requests per second. The rate of the LAN (or throughput between each two end systems) is 10Mbps, while the rate of the access link is 1.5Mbps. The web page is an HTML file of negligible size, with reference to 3 objects of 50 Kbits each, each one fitting in one single packet. HTTP requests and TCP connection establishment messages have negligible sizes.

1. a) [5 pts] Compute the average LAN utilization and the access link utilization.

2. b) [5 pts] If the RTT between an end system in the institutional network and the remote server is 5 seconds, compute the average time to retrieve the whole web page in function of RTT in case of 1) non-persistent, non-parallel, non-pipelined HTTP; 2) persistent, non-parallel, non- pipelined HTTP, 3) persistent, non-parallel, pipelined HTTP, and 4) non-persistent, maximum 2 parallel connections, non-pipelined. (Assume the bottleneck link between users and remote web server is the access link)

3. c) [5 pts] Now consider that a web cache (proxy) is added to the institutional network, and for 40% of the requests it can send the local copy of the web page instead of requesting it to the remote web server. Re-compute the average LAN utilization and the access link utilization for this new case.

4. d) [10 pts] If the RTT between two end systems in the institutional network is RTTlan = 50 msec, compute the savings in the average time to retrieve the whole web page between the case in a) and the case in c) in case of non-persistent, non-parallel, non-pipelined HTTP (Assume the bottleneck link between users and remote web server is the access link).

5. e) [5pts] Re-compute the savings as in d) but in case of a persistent, non-parallel, pipelined HTTP.

Remote Server Public Internet 1.5 Mbps access link Institutional network 10 Mbps LAN Usr 1 Usr 2 Usr 3 Usr N Remote Server Public Internet 1.5 Mbps access link Institutional network 10 Mbps LAN Usr 1 Usr 2 Usr 3 Usr N