Questions from Computer Networks by Athenaeum

Chapter	Problem Number
1	8	Two networks each provide reliable connection-oriented service. One of them offers a reliable byte stream and the other offers a reliable message stream. Are these identical? If so, why is the distinction made? If not, give an example of how they differ.
	11	What are two reasons for using layered protocols?
5	34	In both IP and ATM, the checksum covers only the header and not the data. Why do you suppose this design was chosen?
6	1	In our example transport primitives of figure 6-3, LISTEN is a blocking call. Is this strictly necessary? If not, explain how a nonblocking primitive could be used. What advantage would this have over the scheme describe in the text?
	10	What happens when the user of the transport entity given in Figure 6-20 sends a zero length message? Discuss the significance of your answer.
	23	Why does UDP exist? Would it not have been enough to just let user processes send raw IP packets?
7	38	When are external viewers needed? How does a browser know which one to use?
	24	Some email systems support a header field Content Return: It specifies whether the body of a message is to be returned in the event of no delivery. Does this field belong to the envelope or to the header?
	29	Suppose that someone sets up a vacation daemon and then sends a message just before logging out. Unfortunately, the recipient has been on vacation for a week and also has a vacation daemon in place. What happened next? Will canned replies go back and forth until somebody returns?

Figure 6-3

Primitive	TPDU sent	Meaning
LISTEN	(none)	Block until some process tries to connect
CONNECT	CONNECTION REQ.	Activity attempt to establish a connection
SEND	DATA	Send information
RECEIVE	(none)	Block until a DATA TPDU arrives
DISCONNECT	DISCONNECTION REQ.	This side wants to release the connection