1. [6marks]

   Consider two hosts, A and B, connected by a single link of rate R = 2 Mbps. Suppose that the two hosts are separated by m = 50 km, and the propagation speed along the link is s = 2.5x105 km/sec. Host A is to send a packet of size L = 100 bytes to Host B.

   a) Calculate the propagation delay, dprop. b) Determine the transmission time of the packet, dtrans. c) Ignoringprocessingandqueuingdelays,whatistheend-to-enddelay?

2. [4marks]

   Consider an HTTP client that wants to retrieve a Web document at a given URL. The IP address of the HTTP server is initially unknown. What application-layer and transport-layer protocols are needed in this scenario?

3. [6marks]

   UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8-bit bytes: 01010010, 01100110, 01110110. (Note that although UDP and TCP use 16-bit words in computing the checksum, for this problem you are being asked to consider 8-bit sums.)

   1. a) With the 1s complement scheme, how does the receiver detect errors?

   2. b) What is the 1s complement of the sum of these 8-bit bytes? Show your work step by step.

4. [6marks]

   Suppose Host A sends two segments to Host B back-to-back over a TCP connection. The 1st and 2nd segments contain 75 and 40 bytes of data, respectively. In the first segment, the sequence number is 125, the source port number is 400, and the destination port number is 80. Host B sends an acknowledgment whenever it receives a segment from Host A.

   1. a) What are the sequence number, source port number, and destination port number in the 2nd segment sent from Host A to B?

   2. b) If the 1st segment arrives before the 2nd segment, what is the acknowledgment number, the source port number, and the destination port number in the acknowledgment of the 1st arriving segment?