P6
a
b
c
d
Chapter 2.
R8
List the four broad classes of services that a transport protocol can provide. For each of the service classes, indicate if either UDP or TCP (or both) provide such a service.
P3
Read RFC 959 for FTP. List all of the client commands that are supported by the RFC.
Chapter 3.
R4
Describe why an application developer might choose to run an application over UDP rather tha TCP.
R12
Visit the Go-Back-N Java applet at the companion Web site.
a. Have the source send five packets, and then pause the animation before any of the five packets reach the destination. Then kill the first packet and resume the animation. Describe what happens.
b. Repeat the experiment, but now let the first packet reach the destination and kill the first acknowledgement. Describe again what happens.
c. Finally, try sending six packets. What happens?
R13
Repeat R12, but now with the Selective Repeat Java applet. How are Selective Repeat and Go-Back-N different?
P13
Consider a reliable data transfer protocol that uses only negative acknowledgements. Suppose the sender sends data only infrequently. Would a NAK-only protocol be preferable to a protocol that uses ACKs? Why? Now suppose the sender has a lot of data to send and the end-to-end connection experiences few losses. In this second case, would a NAK-only protocol be preferable to a protocol that uses ACKs? Why?
Chapter 4.
P10
Consider a router that interconnects three subnets: Subnet 1, Subnet 2, and Subnet 3. Suppose all of the interfaces in each of these three subnets are required to have the prefix 223.1.17/24. Also suppose that Subnet 1 is required to support up to 125 interfaces, and Subnet 2 and 3 are each required to support up to 60 interfaces. Provide three network addresses (of the form a.b.c.d/x) that satisfy these constraints.
P11
Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has the following forwarding table:
| Prefix Match | Interface |
|---|---|
| 1 | 0 |
| 11 | 1 |
| 111 | 2 |
| otherwise | 3 |
For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range.
Chapter 8.
R3
Suppose N people want to communicate with each of N-1 other people using symmetric key encryption. All communication between any two people, i and j, is visible to all other people in this group of N, and no other person in this group should be able to decode their communication. How many keys are required in the system as a whole? Now suppose that public key encryption is used. How many keys are required in this case?