川大软件学院2012计算机网络_A闭_

（7）In an Ethernet frame, the preamble is responsible for ______ A) collision detection B) error detection C) synchronization of the receiver’s clock to the sender’s clock. D) multiplexing/ demultiplexing （8）What is the main difference between stop-and-wait and pipelined reliable data transfer protocol? A) The pipelined protocol uses the NAK packets, whereas in the stop-and-wait protocol senders always wait for ACK packets. B) With the pipelined protocol, the sender can send several packets in row, whereas in the stop-and-wait protocol the sender cannot send the packets in row.
（16） During an FTP session the control connection is opened _______. A) once B) twice C) many times D) none of the choices are correct
311015040 计算机网络（A 闭）
Tprop
and the
has to be satisfied to guarantee that a node always detects a collision? B).
Ttrans 2T prop
C)
Ttrans Tprop
D) .
Ttrans 2Tprop
2. Fill in the blank ( 15 points, 1.5 point for each blank )。 （1）Suppose host A sends host B one TCP segment with sequence number 800, acknowledgement number 580, and 40 bytes of data. Then the sequence number in the acknowledgement to this segment is [ ① ] （2） Let’s assume there is 8-bit piece data 11001001, and the CRC is applied to it with generator 1001. Thus the CRC bits should be [ ② ] （3）The flag [ ③ ] in TCP segment header is used during the shutdown of a TCP connection. （4）In a TCP connection , there is a timeout event when the value of threshold is 32 and the size of congestion window is 16. According to the TCP congestion control policy, the new value of threshold should be [ ④ ] and the new size of congestion window should be [ ⑤ ].If there is a duplicate ACK event, the new value of the threshold should be [ ⑥ ] and the new size of congestion window should be [ ⑦ ]. （5）Suppose the IP address of a host is 192.168.5.121, and its subnet mask is 255.255.255.248, then the netid of the host is [ ⑧ ], and the broad cast address of the network is [ ⑨ ] （6）In CSMA/CD, after the 4th collision, the probability that a node chooses K=4 is [ ⑩ ] 3. True or False ( 10 points, 1 point for each statement )。 （1） Switches will decrease the TTL field in the IP header. （2） In the 5-layer Internet reference model, network layer handles point-to-point functions while transport layer handles end-to-end functions. （3） Wireless networks can perform collision detection
（3）Transport-layer packet is called ______. A) message B) segment C) datagram D) frame
（4）Among the following applications, which one is not suitable for P2P architecture. A) file sharing B) video streaming （5）A Web cache _______. A) can help prevent DoS attacks. B) is a network entity that guarantees anonymity of Internet traffic. C) responds to HTTP requests on the behalf of a Web server. D) makes use of cookies to reduce the response time for a client request. （6）In TCP, the timeout interval is a function of ______: A) estimated RTT at the sender C) the size of buffer at the receiver B) MSS and the overhead of a segment D) the size of sending window C) instant message D) electronic banking
（2）In the 1-persistent approach in CSMA, when a station finds an idle line, it _______. A) sends immediately C) waits 1 s before sending B) waits 0.1 s before sending D) waits a time equal to (1 - p) seconds before sending
Ttrans
B) peer-to-peer; client-server D) peer-to-peer; peer-to-peer
（20） In the CSMA/CD protocol, what condition on the transmission delay propagation delay T Tprop A) trans
311015040 计算机网络（A 闭）
1. Multiple Choice (30 points, 1.5 points for each question)
2011-2012-2
（1）Which of the following protocol layers is not explicitly part of the TCP/IP architecture? A) application B) session C) data link D) Transport
（17） DHCP is a (an) ___________ layer protocol. A) application B) transport C) network
2011-2012-2
D) data-link
（18） In a centralized P2P network, the directory system uses the ____ paradigm; the storing and downloading of the files are done using ____ paradigm. A) client-server; client-server C) client-server; peer-to-peer （19） RIP uses the services of _______. A) TCP B) IP C) UDP D) None of the choices are correct
（13） ____ is an interdomain routing protocol using path vector routing. A) BGP B) RIP C) OSPF D) None of the choices are correct
（14） The use of hierarchy in routing tables can ________ the size of the routing tables. A) reduce C) neither reduce nor increase （15） IP is a _________ protocol. A) connection-oriented unreliable C) connectionless unreliable B) connection-oriented reliable D) connectionless reliable B) increase D) None of the choices are correct
（11） When a user retrieve his email from mail server, which of following protocols can’t be used? A) POP3 B) HTTP C) IMAP D) SMTP
（12） In the _______ random-access method collision is avoided. A) CSMA/CD B) CSMA/CA C) ALOHA D) token-passing
311015040 计算机网络（A 闭）
2Leabharlann Baidu11-2012-2
C) With the pipelined protocol, the receiver must send one ACK for several packets (cumulative ACK), whereas in the stop-and-wait protocol the receiver can not send the cumulative ACK. D) The pipelined protocol uses timeouts, whereas the stop-and-wait protocol does not use the timeout. （9）Given that the requested information is not available at any intermediate databases, a purely recursive DNS query from a requesting host would follow the path ______: A) Root name server; TLD name server; local name server; authoritative name server. B) authoritative name server; TLD name server; Root name server; local name server C) TLD name server; Root name server; local name server; authoritative name server; D) local name server; Root name server; TLD name server; authoritative name server; （10） Which of the following nodes belongs to the network core? ______ A) a Web Server C) a Router with NAT service B) a Host with Win2003 Server D) a Supernode on Skype Network