【文章內(nèi)容簡介】 ntrol. Also, some applications do not need the reliable data transfer provided by TCP.2. （教材R4）Why is it that voice and video traffic is often sent over TCP rather than UDP in today39。s Internet. (Hint: The answer we are looking for has nothing to do with TCP39。s congestioncontrol mechanism.)A: Since most firewalls are configured to block UDP traffic, using TCP for video and voice traffic lets the traffic though the firewalls.3. （教材R5）Is it possible for an application to enjoy reliable data transfer even when the application runs over UDP? If so, how? A: Yes. The application developer can put reliable data transfer into the application layer protocol. This would require a significant amount of work and debugging, however.4. （教材R6）Consider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source port number X and destination port number y. What are the source and destination port numbers for the segments traveling from Host B to Host A? A: Source port number y and destination port number x.5. （教材R7）Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B each send a UDP segment to Host C with destination port number 6789. Will both of these segments be directed to the same socket at Host C? If so, how will the process at Host C know that these two segments originated from two different hosts? A: Yes, both segments will be directed to the same socket. For each received segment, at the socket interface, the operating system will provide the process with the IP addresses to determine the origins of the individual segments.6. （教材R9）In our rdt protocols, why did we need to introduce sequence numbers? A: Sequence numbers are required for a receiver to find out whether an arriving packet contains new data or is a retransmission.7. （教材10）In our rdt protocols, why did we need to introduce timers? A: To handle losses in the channel. If the ACK for a transmitted packet is not received within the duration of the timer for the packet, the packet (or its ACK or NACK) is assumed to have been lost. Hence, the packet is retransmitted.8. （教材R14）Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 90。 the second has sequence number 110. a. How much data is in the first segment?b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment that Host B sends to Host A, what will be the acknowledgment number?A: a) 20 bytes b) ack number = 909. （教材R15）True or false? a. The size of the TCP RcvWindow never changes throughout the duration of the connection.b. Suppose Host A is sending Host B a large file over a TCP connection. The number of unacknowledged bytes that A sends cannot exceed the size of the receive buffer.c. Host A is sending Host B a large file over a TCP connection. Assume Host B has no data to send Host A. Host B will not send acknowledgments to Host A because Host B cannot piggyback the acknowledgmens on data.d. The TCP segment has a field in its header for RcvWindow.e. Suppose Host A is sending a large file to Host B over a TCP connection. If the sequence number for a segment of this connection is m, then the sequence number for the subsequent segment will necessarily be m + 1.f. Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. The current value of Timeoutrnterval for the connection will necessarily be1 sec.g. Suppose Host A sends one segment with sequence number 38 and 4 bytes of data over a TCP connection to Host B. In this same segment the acknowledgment number is necessarily 42.A: a) false。 b) false。 need consider retransmit packetc) false。d) true。e) false。f) false。g) false。10. （教材P1）Suppose client A initiates a Telnet session with Server S. At about the same time, client B also initiates a Telnet session with Server S. Provide possible source and destination port numbers for a. The segments sent from A to S.b. The segments sent from B to S.c. The segments sent from S to A.d. The segments sent from S to B.e. If A and B are different hosts, is it possible that the source port number in the segments from A to S is the same as that from B to S?f. How about if they are the same host?A: 11. （教材P2）Consider Figure . What are the source and destination port values in the segments flowing from the server back to the clients39。 processes? What are the IP addresses in the networklayer datagram carrying the transportlayer segments? A: Suppose the IP addresses of the hosts A, B, and C are a, b, c, respectively. (Note that a,b,c are distinct.)252。 To host A: Source port =80, source IP address = b, dest port = 26145, dest IP address = a252。 To host C, left process: Source port =80, source IP address = b, dest port = 7532, dest IP address = c252。 To host C, right process: Source port =80, source IP address = b, dest port = 26145, dest IP address = c12. （教材P19）Answer true or false to the following questions and briefly justify your answer: a. With the SR protocol, it is possible for the sender to receive an ACK for a packet that falls outside of its current windowb. With GBN, it is possible for the sender to receive an ACK for a packet that falls outside of its current window.c. The alternatingbit protocol is the same as the SR protocol with a sender and receiver window size of 1.d. The alternatingbit protocol is the same as the GBN protocol with a sender and receiver window size of 1.Answer:a) True. Suppose the sender has a window size of 3 and sends packets 1, 2, 3 at t0 . At t1 (t1 t0) the receiver ACKS 1, 2, 3. At t2 (t2 t1) the sender times out and resends 1, 2, 3. At t3 the receiver receives the duplicates and reacknowledges 1, 2, 3. At t4 the sender receives the ACKs that the receiver sent at t1 and