Question

Suppose an HTML file references 3 very small objects (therefore total of 4 objects including the HTML file).

The HTML file and the referenced objects are stored in a different server i.e. One server that has the HTML file and another server that contains all the referenced objects.

Neglecting transmission times, home much would have elapsed for all the objects to be loaded/received in

• Part 1 (5 points): Persistence connection scenario
• Part 2 (5 points): Non- persistence connection scenario

Assume that the round-trip delay is 30ms for each back and forth communication (even for establishing TCP connection). It is the same for both the servers.

Hint: Same connection CANNOT be used across different servers.

Answer 1

In both the cases (persistent and non persistent), it takes 2RTT (round trip time) to establish a connection

Part 1 Persistent Connection scenario

A persistent connection takes 2 RTT for the connection and then transfers as many objects as required over this single connection.

Hence total time for 5 objects = 2RTT( connection establishment) + 5 RTT = 7 RTT

As RTT is given as 40 ms

Therefore the total time for receiving the packets would be

7*40 = 280 ms

Part 2 Non persistent scenario

In addition to the initial connection establishment process, a non persistent connection has to establish and close connection for each and every object.

Hence the total time taken in this case would be

2RTT ( connection establishment) + 2* 5 RTT

2RTT+10RTT = 12RTT

Substituting RTT = 40 ms

12 * 40 = 480 ms

Part 1 : Persistent Connection : time taken : 280ms

Part 2 : Non Persistent Connection : 480ms