Question

Problem # 1 (30 points): Suppose within your Web browser you click on a link to obtain a web page Suppose that the IP address for the associated URL is not cached in your local host, so that a DNS look- up is necessary to obtain the IP address. Suppose that two (2) DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT of RTT1 and RTT2. Further suppose that the Web page associated with the link contains exactly one object; the base HTML file. Let RTTo denote the RTT between the local host and the server containing the object. Assuming /rans transmission time of the base HTML file, find a. (6 points) The amount of time that elapses from when the client clicks on the link until the client receives the base HTML file b. Suppose the base HTML file indexes two (2) more objects. The first indexed object resides on the same server hosting the base HTML file. The second indexed object resides on a different server than the server hosting the base HTML file, and the IP address of such a server is already cached in your local host. Assume that RTTo denotes the RTT between the local host and each server containing an object. Using the same assumptions used in part (a) for the base HTML file, and assuming the transmission time for each indexed object is /rans, find the total amount of time that elapses from when the client clicks on the link until the client receives all objects (including the base HTML file) with i. (6 points) nonpersistent HTTP with no parallel TCP connections ii. (6 points) nonpersistent HTTP with parallel TCP connections (assume that parallel TCP connections can be made to different servers at the same time) iii.(6 points) persistent HTTP without pipelining ˇ· (6 points) persistent HTTP with pipelining

Answer 1

When a user clicks on a link, the browser establishes a TCP connection with the server and nds a request t a response that contains the requested object to the client. This process takes two round-trip times (RTT) It is given in the problem that the round-trip times (RTT) are as follows: RTT between local host and DNS server 1= RTT RTT between local host and DNS server 2- RTT2 and so on, RTT between local host and DNS server n= RTT RTT between local host and server RTTo and Transmission time of the object-o

Time taken for DNS look upRTT,+ RTT+...RTT Since RTT between local host and server is RTTo Time to establish TCP connection RTT Time to request and receive the object is, = RTT, + transmission time of object =RTT. Theretore, the amount f tme at elapses rom when a user cicks the ink until he object s received by the client is, Time taken for DNS look up Time to establish TCP connection+Time to send request and receive object.

a Non- persistent HTTP with no parallel TCP connections: Already know for object 1 from above, now we need to add the time for the next 7 objects and not thenext three objects. . Total elapses time-RTT + + RTT, + 2RTG + 3x (2RTL) RTTİ + + RTT, + 8RTTO b. Non -persistent HTTP with four parallel TCP connections Total four parallel files will be transferred simultaneously using five independent connections and remaining three files needs 2RTT Total elapses time-RTT + "" + RTT, + 2RTI。+2RTTO