计算机通信网review含答案.pdf

1 One Multiple Choice Questions Q 1 What is the IEEE protocol for Ethernet A 800 B 801 C 802 D 803 E 804 Q 2 What is the hexadecimal equivalent of the Ethernet address 01011010 00010001 01010101 00011000 10101010 00001111 A 5A 11 55 18 AA 0F B 5A 11 55 18 AC 0F C 5A 14 55 18 AA 0F D 5A 11 55 18 BA 0F E 5A 11 55 18 AA F0 Q 3 IP is presented on which of the following TCP IP layers A Physical Layer B Application Layer C Data Link Layer D Presentation Layer E Network Layer Q 4 Which of the following device does Network layer packet forwarding A Router B Hub C Bridge D Modem E Repeater Q 5 What is the generator polynomial for 1001101 A X 5 X 3 X 2 X B X 6 X 3 X 1 C X 6 X 4 X 2 1 D X 6 X 3 X 2 1 E X 6 X 5 X 2 1 Q 6 f the data unit is 111111 the divisor 1010 and the remainder 110 what is the dividend at the receiver A 111111110 B 111111101 C 111101110 D 111110111 E 101111111 2 Q 7 operates only at the data link layer A UDP B ARQ C FTP D ICMP E None of the above Q 8 One of the well known ports used by TCP is A HTTP B Echo C SNMP D ICMP E ATM Q 9 A connects two LANs with different subnet A Bridge B Switch C Hub D Modem E Repeater Q 10 Class C network 192 168 9 0 Mask 255 255 255 224 What is the subnets range for the above network A 192 168 9 0 224 B 192 168 9 1 224 C 192 168 9 0 254 D 192 168 9 1 254 E 192 168 9 0 255 Q 11 Which of the four sources of delay depend on the packet size A Transmission delay B Propagation delay C Processing delay D Queueing Q 12 Which of the following is not belonging to communication links A Fiber B Routers C Copper D Radio Q 13 Which of the following statement is incorrect A Protocols define format of msgs sent and received among network entities 3 B Protocols define order of msgs sent and received among network entities C Protocols define actions taken on msg transmission and or receipt of a message D Protocols define communication infrastructure of a network Q 14 Which of the following statement about web is correct A Web is an application programs and it is runing at core of network B Web browser server is runing on a client server model C Web browser is a client program it is a always on program D Web server send messages to web browser to request service Q 15 Which of the following program is not running at P2P model A eDonkey B BitTorrent C E mail D Skype Q 16 Which of the following protocol is not using TCP A DNS B FTP C HTTP D SMTP Q 17 Which of the following is incorrect about Circuit Switching A Link bandwidth is gurranteed B Resource is shared by all users C Call setup is required D End to end resources is reserved for call Q 18 How long does it take to send a file of 320 000 bits from host A to host B over a circuit switched network If all links are 1 536 Mbps each link uses TDM with 24 slots sec and 500 msec to establish end to end circuit A 5 sec B 0 5 sec C 5 5 sec D 4 5 sec Q 19 Which of the following is not the source of packet delay A Nodal processing B Transmission C Router interface D Queueing Q 20 Which of the following is incorrect about client server architecture A Server directly communicated with each other 4 B Server is a always on host C Clients communicate with server D Server has a permanent IP address Q 21 Which of the following is incorrect about addressing processes A Many processes can be running on same host B The IP address of the host on which the process runs is sufficient for identifying the process C A port number is associated with the process on the host D On an same host may have many port number Q 22 Which of the following is not provided by TCP service A Flow control B Congestion control C Reliable transport D Timing Q 23 Which of the following is not the reason for UDP existing A Provide reliable data control B Simple C No connection D Small segment header Q 24 Which of the following is not the three Key network lay functions A Forwarding B Routing C Connection setup D Reliable transfer Q 25 How many subnets in the following network 5 A 3 B 4 C 5 D 6 Q 26 What is the hexadecimal equivalent of the IP address 202 204 24 35 A CACC1823 B CCCA1823 C CACC2435 D CCCA2435 Two True or False Questions The red are TRUE the black are FALSE Q 1 An ARP request is unicast An ARP reply is broadcast Q 2 The number of addresses in class C is smaller than the needs of most organizations Q 3 UDP is a connectionless unreliable protocol that has flow and error control Q 4 Every host implements the transport layer Q 5 Every router implements the transport layer Q 6 Every router implements the network layer Q 7 Every switch implements the network layer Q 8 Every switch implements the data link layer Q 9 It is possible that a router implements several types of link layers Q 10 It is the network layer s responsibility to forward packets reliably from the source to the destination Q 11 Suppose you access a web page from your computer When you examine a packet resulting from this access on an Ethernet link you find first the HTTP header followed by the TCP header followed by the IP header followed by the Ethernet header Q 12 The advantage of packet switching over circuit switching is more pronounced for bursty traffic the rate fluctuates a lot than for smooth traffic the rate fluctuates little or not at all Q 13 In a datagram network such as IP routers keep track of connections between end systems Q 14 In a circuit switched network switches allocate resources link capacity buffer space to every circuit Q 15 A router decides on a route for an IP packet based on its source and destination address Q 16 A cable TV access network is a shared medium Q 17 When you download a web page it results always in exactly one TCP connection Q 18 You issue the command ipconfig and observe the following output lo Link encap Local Loopback inet addr 127 0 0 1 Mask 255 0 0 0 UP LOOPBACK RUNNING MTU 16436 Metric 1 RX packets 126647 errors 0 dropped 0 overruns 0 frame 0 TX packets 126647 errors 0 dropped 0 overruns 0 carrier 0 collisions 0 txqueuelen 0 RX bytes 24457818 23 3 Mb TX bytes 24457818 23 3 Mb 6 Your computer is currently connected to the network Q 19 The network layer modifies the UDP header Q 20 Tier 1 ISPs Internet Service Provider are customers of Tier 2 ISPs Q 21 The phone network uses circuit switching Q 22 Assume we send packets of some fixed size through a network and assume routes do not change Then the only random component in total packet delay is the queuing delay Q 23 Stop and Wait Go back N and Selective reject are examples of continuous ARQ Q 24 The longer the frames or the shorter the propagation time the higher utilization can be achieved in CSMA LANs Q 25 With Go back N error control protocol it is not required that each individual frame be acknowledged Q 26 IEEE 802 2 defines the logical link control layer and provides three types of services 1 unacknowledged connectionless service 2 connection mode service and 3 acknowledged connectionless service Q 27 Each host on a public IPv4 Internet network is assigned a unique 32 bit IP address that is used in all communication with that host Q 28 All nodes connected to the Internet must implement UDP Q 29 Media Access Control is a function of the data link layer Q 30 An Internet router connecting N subnetworks requires N 1 IP addresses Q 31 UDP provides connectionless service and delivers packets quickly In case of packet loss UDP does not provide retransmission Q 32 UDP is the preferred over TCP for transferring a real time voice over IP networks Q 33 Circuit switching networks require signaling and control for establishing circuits Q 34 One of the ways to reduce transmission delay is to use a higher speed transmission system Q 35 Routers use the destination network not the destination computer when forwarding a packet Q 36 The Sequence number used in TCP represents a byte octet in segment payload Q 37 The source IP address used in IP represents 32 byte octet in segment payload Q 38 TCP uses 4 way handshake for connection setup Q 39 Hub bridge switch and router are of network segment interconnecting devices in a LAN Q 40 Queue delay and loss is due to router input port buffer overflow Q 41 Routers typically have multiple interfaces Host typically has one interface Q 42 In Client Server model server is normally an always on host and has a dynamic IP address Q 43 is not a valid url Three Short Answer questions Chapter one 7 重点 协议原理和网络层次的划分重点 协议原理和网络层次的划分 典型问题 典型问题 1 What are the five layers of the internet model and what do each of these layers do Describe using a diagram the five layers in the network model used in the book and what each of the layers do Put two examples of standards protocols on each of your layers in the diagram Do this in detail explaining how a message is transmitted from one computer to another using this model 8 Chapter two 重点 两种不同的应用层服务模式 重点 两种不同的应用层服务模式 C S 与与 P2P HTTP 基本原理基本原理 传输层协议对应用层的服务传输层协议对应用层的服务 典型问题 典型问题 1 What information is used by a process running on one host to identify a process running on another host Port Numbers 2 Why do HTTP FTP SMTP POP3 and IMAP run on top of TCP while DNS run on UDP HTTP FTP SMTP POP3 and IMAP need reliable transmission but DNS do not 3 The following is a HTTP message head what information you can read from it GET somedir page html HTTP 1 1 Use Get method to get the somedir page html by HTTP 1 1 protocol Host www someschool edu Host name for the above request User agent Mozilla 4 0 Header for identifying the browser Connection close connection type Accept language fr language Chapter three 重点 两种传输层服务的区别 即面向连接的服务与无连接服务的区别重点 两种传输层服务的区别 即面向连接的服务与无连接服务的区别 可靠传输的原理可靠传输的原理 UDP 与与 TCP 协议格式以及各字段的含义协议格式以及各字段的含义 典型问题 典型问题 1 List the two Internet s transport protocols What is the key difference between them TCP reliable flow control congestion control UDP unreliable simple 2 How many bytes in TCP or UDP headers TCP 20 bytes UDP 8 bytes List the key fields for TCP UDP Header and explain their functions briefly 3 Using TCP How does the sender know that its packets make it to the destination Acknowledgement How does the sender detect when a packet gets lost Time out What does the sender do to recover from packet loess Retransmission Is it possible for a receiver to receive more than one copy of the same packet Explain the reasons Yes When time s out sender retransmits the new same package and the receiver receives the last same package 4 What happens when queue becomes too long Lose 9 Chapter four 重点 网络层的两大功能 路由于转发重点 网络层的两大功能 路由于转发 IP 协议的格式以及字段含义 协议的格式以及字段含义 IP 地址 子网掩码 子网分割地址 子网掩码 子网分割 路由算法原理路由算法原理 典型问题典型问题 1 What are the length of IPv4 and IPv6 IPv4 32 bits IPv6 128 bits How many bytes in the IP v4 headers 20 bytes List the key field for IP header and explain their functions briefly Why do we need for improvement of IPv4 what are the advantages of IPv6 IPv4 is not sufficient for every device IPv6 is sufficient 2 Suppose that you have been assigned IP address 122 228 0 0 and have 10 networks in your organization that you wish to remain distinct Give the subnet mask Give the subnet addresses o