20200217

Pagina 1

Fundamentals of Communication Networks Prof. A. Pattavina II exam – 17 February 2020 Surname and name: (upper case) Signature: (your readable signature) Matricola ID: Pag. 1/10 1 - Exercise* (7 points) The network in the figure includes 3 routers (R1, R2, R3), one client (C) and one HTTP server (S). Link rates and delay of each link are also shown in the figure. The network includes also other three hosts (A, B, D) that terminate long lasting flows interfering with the interaction between client C and server S: 4 flows between A and D, 4 flows between B and D. We assume that the HTTP client in C is willing to download a web page from server S. The capacity of the sequence of links between S and C is limited by the link that represents the network bottleneck for the C -to-S interaction. The web page is composed by a base document (html) of Lhtml = 3 kbyte and by 12 images each of Lobj = 15 kbyte. Assuming that the control messages to open the TCP connection and the GET HTTP messages have negligible length, compute the time taken for the full download of the web page (base document and 12 images) in the following cases: a) client C uses only one persistent TCP connection for the base document and the image; b) client C uses non-persistent TCP connections and whenever possible TCP connections are opened in parallel (no pipelining is adopted); c) client C uses non-persistent TCP connections without the possibility of opening parallel connections. Fair sharing of resources is adopted in order to compute the rate of different TCP connections. Write here the final numerical results and the symbolic expressions and comput ations in the following page a) Ttot,a= ________________________________________ b) T tot,b= ________________________________________ c) Ttot,c =…