3 15 Points HTTP from 2015 Midterm similar to problems 78 in

3. (15 Points) HTTP (from 2015 Midterm, similar to problems 7-8 in Ch.2)

You open your browser and you click on a URL. Assume that the webpage associated with the URL consists of a small HTML file and 2 small images, all stored on the same webserver. Let RT Tcs be the RTT from the client host to the webserver containing the URL. The IP address of the webserver is not cached at the local host but is cached at your local DNS server. Let RT TDNS be the RTT from the client host to the local DNS server. What is the total delay from the time you click on the webpage until the time that the entire webpage is displayed on your browser? Take into account all messages sent/received by the client host, including DNS, HTTP and TCP-related messages.

Consider two cases: (a) Persistent HTTP without pipelining. (b) Non-persistent HTTP with 2 parallel connections.

Solution

The following preliminary steps are required:

First, IP address of the web server from the local DNS server is obtained. it gives RTTDNS time. we must create a TCP connection with the server. There are three messages in a TCP handshake: SYN, ACK and SYNACK. The rst two take RTTCS time. The third one is also used to send the HTTP request and is accounted for below. Third, we send the HTTP request for the HTML le and we get the request. This takes RTTCS time. Note: since all messages and objects are “small” we can neglect the transmission delays and focus on RTTs. Those of you who explicitly considered the transmission bandwidth are not penalized, though. The part above are common to (a) and (b). The dierentiation starts here.

In the persistent connection, the existing TCP connection is used. The default mode of HTTP uses persistent connections with pipelining . This means that the requests for the two objects will be send back to back; and because the transmission time is negligible, essentially at the same time.

In the second case the tcp is not uses because non persistent technique which is used withy 2 parallel connections will not be effecteed for the two objects the extra time will show the negligible points in it.