Data Communication

1. short answer

e. Consider a TCP connection between hosts A and B. Suppose that the TCP segments from A to B have source port number x and destination port number y. What are the source and destination port numbers for the segments traveling from B to A?

f. It is said that a TCP connection "probes" the network path it uses for available bandwidth. What is meant by that?

g. Explain the process of a three way handshake in TCP that initiates communications on the Internet.

h. The UDP server described in class needed only one socket, whereas the TCP server needed two sockets. Why? If the TCP server were to support N simultaneous connections, each from a different client host, how many sockets would the TCP server need? Express your answer as an equation.

i. How does the congestion window (cwnd) increase on the receipt of an ACK during slow-start? During congestion avoidance?

j. What controls when the transition between slow-start and congestion avoidance occurs?

k. In the basic TCP Tahoe, what happens to cwnd and the slow-start threshold when loss is detected?

3. A user in Norfolk, connected to the internet via a 5 Mb/s connection, retrieves a 50 KB (B=bytes) web page from a web server in California, where the page references 4 images of 300 KB each. Assume that the one way propagation delay is 20 ms. a. Approximately how long does it take for the page (including images) to appear on the users screen, assuming persistent HTTP? b. How long would it take using non-persistent HTTP (assume a single connection) ?