Applications
List five nonproprietary Internet applications and the application-layer protocols that they use.
DNS
What are the root servers?
Explain the invariant that holds over the DNS namespace with regards to zones.
What is the difference between iterative and recursive queries? Under what circumstances would one want to use iterative queries?
HTTP
Obtain the HTTP/1.1 specification (RFC 2616). Answer the following questions:
1. Explain the mechanism used for signaling between the client and server to indicate that a persistent connection is being closed. Can the client, the server, or both signal the close of a connection.
2. What encryption services are provided by HTTP?
Delay with Caching
Consider Figure 2.11, for which there is an institutional network connected to the Internet. Suppose that the average object size is 900,000 bits and that the average request rate from the institution's browsers to the origin servers is 1.5 requests per second. Also suppose that the amount of time it takes from when the router on the Internet side of the access link forwards and HTTP request until it receives the response is two seconds on average (see Section 2.2.6). Model the total average response time as the sum of the average access delay (that is, the delay from Internet router to institution router) and the average Internet delay. For the average access delay, use Δ/(1 - ΔΒ), where Δ is the average time required to send an object over the access link and Β is the arrival rate of objects to the access link.
1. Find the total average response time.
Calculating Delay
This elementary problem begins to explore propagation delay and transmission delay, two central concepts in data networking. Consider two hosts, A and B, connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters, and suppose the propagation speed along the link is s meters/sec. Host A is to send a packet of size L bytes to Host B.
1. Express the propagation delay, d_prop, in terms ofm and s.
2. Determine the transmission time of the packet, d_trans, in terms of L and R
3. Ignoring processing and queuing delays, obtain an expression for the end-to-end delay
4. Suppose Host A begins to transmit the packet at time t = 0. At time t = d_trans, where is the last bit of the packet?
5. Suppose d_prop is greater than d_trans. At time t = d_trans, where is the first bit of the packet?
6. Suppose d_prop is less than d_trans. At time t = d_trans, where is the first bit of the packet?
Suppose s = 2.5×10^8, L = 100 bits, and R = 28 kbps. Find the distance m so that d_prop equals d_trans.
Sockets
In Java, what is the critical difference between a server socket and a client socket?
Peer to Peer
Compare and contrast how the following are handled in Bittorrent vs. Napster:
RDT 2.1
Consider our motivation for correcting protocol rdt2.1. Show that the receiver, shown in the figure on the following page, when operating with the sender shown in Figure 3.11, can lead the sender and receiver to enter a deadlock state, where each is waiting for an event that will never occur.
Go-Back-N
Consider the GBN protocol with a sender window size of 3 and a sequence number range of 1,024. Suppose that at time t, the next in-order packet that the receiver is expecting has a sequence number of k. Assume that the medium does not reorder messages. Answer the following questions:
1. What are the possible sets of sequence numbers inside the sender's window at time t? Justify your answer.
2. What are all possible values of the ACK field in all possible messages currently propagating back to the sender at time t? Justify your answer