计算机网络概述课件教学1. 课程概述计算机网络是指将分布在不同地理位置的计算机和网络设备通过通信线路连接起来，形成一个互相通信和共享资源的网络系统。
本章将介绍计算机网络的基本概念和组成部分，帮助学生理解计算机网络的工作原理和应用。
2. 计算机网络基础知识2.1 计算机网络的定义计算机网络是指通过通信线路连接起来的计算机和网络设备的集合，可以实现数据传输、资源共享和信息交流。
2.2 计算机网络的分类计算机网络可以根据地理范围和连接方式进行分类。
按地理范围分为局域网（LAN）、城域网（MAN）、广域网（WAN）和互联网（Internet）等；按连接方式分为点对点连接和广播方式。
2.3 计算机网络的拓扑结构计算机网络的拓扑结构指的是计算机和网络设备之间的连接方式，常见的拓扑结构有总线型、星型、环型和网状型。
2.4 计算机网络的协议协议是计算机网络中用于进行数据传输和通信的一种规则或约定。
常见的计算机网络协议包括TCP/IP协议、HTTP协议和FTP协议等。
3. 计算机网络的功能计算机网络具有数据传输、资源共享和信息交流的功能。
3.1 数据传输计算机网络通过通信线路将数据从发送端传输到接收端，实现数据的传输功能。
数据传输可以通过有线传输和无线传输两种方式实现。
3.2 资源共享计算机网络通过共享资源，如打印机、文件服务器和数据库服务器等，实现资源的共享功能。
用户可以通过网络访问和使用远程计算机上的资源。
3.3 信息交流计算机网络通过提供电子邮件、即时通信和远程会议等功能，实现人与人之间的信息交流。
人们可以通过网络进行沟通和合作，方便快捷地共享信息和知识。
4. 计算机网络的应用计算机网络在各个领域都有广泛的应用，如互联网、电子商务、在线教育和远程医疗等。
4.1 互联网互联网是全球最大的计算机网络，连接起了世界各地的计算机和网络设备。
它提供了丰富多样的服务和应用，如电子邮件、网页浏览、在线视频和社交媒体等。
4.2 电子商务电子商务是指通过计算机网络进行商品购买和交易的商业活动。
Chapter 5 The Link Layer and Local Area Network1．A ( ) protocol is used to move a datagram over an individual link.A application-layerB transport-layerC network-layerD link-layer2．The units of data exchanged by a link-layer protocol are called ( ).A datagramsB framesC segmentsD messages3．Which of the following protocols is not a link-layer protocol? ( )A EthernetB PPPC HDLCD IP4．In the following four descriptions, which one is not correct? ( )A link-layer protocol has the node-to-node job of moving network-layer datagrams over a single link in the path.B The services provided by the link-layer protocols may be different.C A datagram must be handled by the same link-layer protocols on the different links in the path.D The actions taken by a link-layer protocol when sending and receiving frames include error detection, flow control and random access.5．Which of the following services can not offered by a link-layer protocol? ( )A congestion controlB Link AccessC Error controlD Framing6．( ) protocol serves to coordinate the frame transmissions of the many nodes when multiple nodes share a single broadcast link.A ARPB MACC ICMPD DNS7．In the following four descriptions about the adapter, which one is not correct? ( )A The adapter is also called as NIC.B The adapter is a semi-autonomous unit.C The main components of an adapter are bus interface and the link interface.D The adapter can provide all the link-layer services.8．Consider CRC error checking approach, the four bit generator G is 1011, and suppose that the data D is 10101010, then the value of R is( ).A 010B 100C 011D 1109．In the following four descriptions about random access protocol, which one is not correct? ( )A I n slotted ALOHA, nodes can transmit at random time.B I n pure ALOHA, if a frame experiences a collision, the node will immediately retransmit it with probability p.C T he maximum efficiency of a slotted ALOHA is higher than a pure ALOHA.D I n CSMA/CD, one node listens to the channel before transmitting.10．In the following descriptions about MAC address, which one is not correct? ( )A T he MAC address is the address of one node’s adapter.B N o two adapters have the same MAC address.C T he MAC address doesn’t change no matter where the adapter goes.D M AC address has a hierarchical structure.11．The ARP protocol can translate ( ) into ( ). ( )A h ost name, IP addressB h ost name, MAC addressC I P address, MAC addressD broadcast address, IP address12．The value of Preamble field in Ethernet frame structure is ( )A 10101010 10101010……10101010 11111111B 10101011 10101011……10101011 10101011C 10101010 10101010……10101010 10101011D 10101010 10101010……10101010 1010101013．There are four steps in DHCP, the DHCP server can complete ( ).A DHCP server discoveryB DHCP server offersC DHCP requestD DHCP response14．In CSMA/CD, the adapter waits some time and then returns to sensing the channel. In the following four times, which one is impossible? ( )A 0 bit timesB 512 bit timesC 1024 bit timesD 1028 bit times15．The most common Ethernet technologies are 10BaseT and 100BaseT. “10” and “100” indicate( ).A the maximum length between two adaptersB the minimum length between two adaptersC the transmission rate of the channelD the transmission rate of the node16．The principal components of PPP include but not( ).A framingB physical-control protocolC link-layer protocolD network-layer protocol17．In the following four options, which service can not be provided by switch? ( )A filteringB self-learningC forwardingD optimal routing18．In the following four services, which one was be required in PPP? ( )A packet framingB error detectionC error correctionD multiple types of link19．The ability to determine the interfaces to which a frame should be directed, and then directing the frame to those interfaces is( ).A filteringB forwardingC self-learningD optimal routing20．In ( ) transmission(s), the nodes at both ends of a link may transmit packets at the same time.A full-duplexB half-duplexC single-duplexD both full-duplex and half-duplex21．Consider the data D is 01110010001, if use even parity checking approach, the parity bit is( ① ), if use odd parity checking approach, the parity bit is( ② ). ( )A ①0 ②1B ①0 ②0C ①1 ②1D ①1 ②022．In the following four descriptions about parity checks, which one is correct? ( )A Single-bit parity can detect all errors.B Single-bit parity can correct one errors.C Two-dimensional parity not only can detect a single bit error, but also can correct that error.D Two-dimensional parity not only can detect any combination of two errors, but also can correct them.23．MAC address is ( ) bits long.A 32B 48C 128D 6424．Wireless LAN using protocol ( ).A IEEE 802.3B IEEE 802.4C IEEE 802.5D IEEE 802.1125．The following protocols are belonging to multiple access protocols except for ( ).A channel partitioning protocolsB routing protocolsC random access protocolsD taking-turns protocols26．Which of the following is not belonging to channel partitioning protocols? ( )A CSMAB FDMC CDMAD TDM27．In the following four descriptions about CSMA/CD, which one is not correct? ( )A A node listens to the channel before transmitting.B If someone else begins talking at the same time, stop talking.C A transmitting node listens to the channel while it is transmitting.D With CSMA/CD, the collisions can be avoided completely.28．( ) provides a mechanism for nodes to translate IP addresses to link-layer address.A IPB ARPC RARPD DNS29．A MAC address is a ( )address.A physical-layerB application-layerC link-layerD network-layer30．Which of the following is correct? ( )A No two adapters have the same MAC address.B MAC broadcast address is FF-FF-FF-FF-FF-FF.C A portable computer with an Ethernet card always has the same MAC address, no matter where the computer goes.D All of the above31．In the following four descriptions, which one is not correct? ( )A ARP resolves an IP address to a MAC address.B DNS resolves hostnames to IP addresses.C DNS resolves hostnames for hosts anywhere in the Internet.D ARP resolves IP addresses for nodes anywhere in the Internet.32．In the LAN, ( )protocol dynamically assign IP addresses to hosts.A DNSB ARPC DHCPD IP33．DHCP protocol is a four-step process: ①DHCP request. ②DHCP ACK. ③DHCP server discovery. ④DHCP server offer(s). The correct sequence is ( )A ①②③④B ③②①④C ③④①②D ①④③②34．In the Ethernet frame structure, the CRC field is ( )bytes.A 2B 4C 8D 3235．In the Ethernet frame structure, the Data field carries the ( ).A IP datagramB segmentC frameD message36．In the following four descriptions, which one is not correct? ( )A Ethernet uses baseband transmission.B All of the Ethernet technologies provide connection-oriented reliable service to the network layer.C The Ethernet 10Base2 technology uses a thin coaxial cable for the bus.D The Ethernet 10BaseT technology uses a star topology.37．Ethernet’s multiple access protocol is ( ).A CDMAB CSMA/CDC slotted ALOHAD token-passing protocol38．In the following four descriptions about CSMA/CD, which one is not correct? ( )A An adapter may begin to transmit at any time.B An adapter never transmits a frame when it senses that some other adapter is transmitting.C A transmitting adapter aborts its transmission as soon as it detects that another adapter is also transmitting.D An adapter retransmits when it detects a collision.39．Which of the following descriptions about CSMA/CD is correct? ( )A No slots are used.B It uses carrier sensing.C It uses collision detection.D All of the above.40．The Ethernet 10BaseT technology uses( )as its physical media.A fiber opticsB twisted-pair copper wireC coaxial cableD satellite radio channel41．For 10BaseT, the maximum length of the connection between an adapter and the hub is ( )meters.A 100B 200C 500D 1042．A ( )is a physical-layer device that acts on individual bits rather than on frames.A switchB hubC routerD gateway43．A hub is a ( )device that acts on individual bits rather than on frames.A physical-layerB link-layerC network-layerD ransport-layer44．A switch is a( )device that acts on frame.A physical-layerB link-layerC network-layerD transport-layer45．In the following four descriptions, which one is not correct? ( )A Switches can interconnect different LAN technologies.B Hubs can interconnect different LAN technologies.C There is no limit to how large a LAN can be when switches are used to interconnect LAN segments.D There is restriction on the maximum allowable number of nodes in a collision domain when hubs are used to interconnect LAN segments.46．The ability to determine whether a frame should be forwarded to some interface or should just be dropped is ( ).A f ilteringB f orwardingC s elf-learningD o ptimal routing47．Which of the following devices is not a plug and play device? ( )A hubB routerC switchD repeater48．Which of the following devices is not cut-through device? ( )A hubB routerC switchD repeater49．In the following four descriptions, which one is not correct? ( )A Switches do not offer any protection against broadcast storms.B Routers provide firewall protection against layer-2 broadcast storms.C Both switches and routers are plug and play devices.D A router is a layer-3 packet switch, a switch is a layer-2 packet switch. 50．Which device has the same collision domain? ( )A HubB SwitchC RouterD Bridge51．IEEE802.2 protocol belong to ( )layerA networkB MACC LLCD physical52．IEEE802.11 protocol defines ( )rules.A Ethernet BusB wireless WANC wireless LAND Token Bus53．In data link-layer, which protocol is used to share bandwidth? ( )A SMTPB ICMPC ARPD CSMA/CD54．When two or more nodes on the LAN segments transmit at the same time, there will be a collision and all of the transmitting nodes well enter exponential back-off, that is all of the LAN segments belong to the same( ).A collision domainB switchC bridgeD hub55．( )allows different nodes to transmit simultaneously and yet have their respective receivers correctly receive a sender’s encoded data bits.A CDMAB CSMAC CSMA/CDD CSMA/CA56．Because there are both network-layer addresses (for example, Internet IP addresses) and link-layer addresses (that is, LAN addresses), there is a need totranslate between them. For the Internet, this is the job of ( ).A RIPB OSPFC ARPD IP57．PPP defines a special control escape byte, ( ). If the flag sequence, 01111110 appears anywhere in the frame, except in the flag field, PPP precedes that instance of the flag pattern with the control escape byte.A 01111110B 01111101C 10011001D 1011111058．The device ( ) can isolate collision domains for each of the LAN segment.A modemB switchC hubD NIC59．In the following four descriptions about PPP, which one is not correct? ( )A PPP is required to detect and correct errors.B PPP is not required to deliver frames to the link receiver in the same order in which they were sent by the link sender.C PPP need only operate over links that have a single sender and a single receiver.D PPP is not required to provide flow control.60．In the PPP data frame, the( ) field tells the PPP receivers the upper-layer protocol to which the received encapsulated data belongs.A flagB controlC protocolD checksum61．PPP’s link-control protocols (LCP) accomplish ( ).A initializing the PPP linkB maintaining the PPP linkC taking down the PPP linkD all of the above62．The PPP link always begins in the ( ) state and ends in the ( ) state. ( )A open, terminatingB open, deadC dead, deadD dead, terminating63．For( ) links that have a single sender at one end of the link and a single receiver at the other end of the link.A point-to-pointB broadcastC multicastD all of the above64．With ( )transmission, the nodes at both ends of a link may transmit packets at the same time.A half-duplexB full-duplexC simplex(单工)D synchronous65．With ( ) transmission, a node can not both transmit and receive at the same time.A half-duplexB full-duplexC simplex(单工)D synchronous66．Which of the following functions can’t be implemented in the NIC? ( )A encapsulation and decapsulationB error detectionC multiple access protocolD routing67．Which of the following four descriptions is wrong? ( )A The bus interface of an adapter is responsible for communication with the adapter’s parent node.B The link interface of an adapter is responsible for implementing the link-layer protocol.C The bus interface may provide error detection, random access functions.D The main components of an adapter are the bus interface and the link interface. 68．For odd parity schemes, which of the following is correct? ( )A 011010001B 111000110C 110101110D 00011011069．( )divides time into time frames and further divides each time frame into N time slots.A FDMB TMDC CDMAD CSMA70．With CDMA, each node is assigned a different ( )A codeB time slotC frequencyD link71．Which of the following four descriptions about random access protocol is not correct? ( )A A transmission node transmits at the full rate of the channelB When a collision happens, each node involved in the collision retransmits at once.C Both slotted ALOHA and CSMA/CD are random access protocols.D With random access protocol, there may be empty slots.72．PPP defines a special control escape byte 01111101. If the data is b1b201111110b3b4b5, the value is( )after byte stuffing.A b1b20111110101111110b3b4b5B b1b20111111001111101b3b4b5C b5b4b30111111001111101b2b1D b5b4b30111110101111110b2b173．MAC address is in ( ) of the computer.A RAMB NICC hard diskD cache74．Which of the following is wrong? ( )A ARP table is configured by a system administratorB ARP table is built automaticallyC ARP table is dynamicD ARP table maps IP addresses to MAC addresses75．NIC works in ( )layer.A physicalB linkC networkD transport76．In LAN, if UTP is used, the common connector is( ).A AUIB BNCC RJ-45D NNI77．The modem’s function(s) is(are) ( ).A translates digital signal into analog signalB translates analog signal into digital signalC both translates analog signal into digital signal and translates digital signal into analog signalD translates one kind of digital signal into another digital signal78．( )defines Token-Ring protocol.A IEEE 802.3B IEEE 802.4C IEEE 802.5D IEEE 802.279．( )defines Token-Bus protocol.A IEEE 802.3B IEEE 802.4C IEEE 802.5D IEEE 802.280．( ) defines CSMA/CD protocol.A IEEE 802.3B IEEE 802.4C IEEE 802.5D IEEE 802.281．The computer network that concentrated in a geographical area, such as in a building or on a university campus, is ( )A a LANB a MANC a WAND the Internet82．The MAC address is ( ) bits long.A 32B 48C 128D 25683．Which of the following four descriptions about MAC addresses is wrong? ( )A a MAC address is burned into the adapter’s ROMB No two adapters have the same addressC An adapter’s MAC address is dynamicD A MAC address is a link-layer address84．Which of the following four descriptions about DHCP is correct? ( )A DHCP is C/S architectureB DHCP uses TCP as its underlying transport protocolC The IP address offered by a DHCP server is valid foreverD The DHCP server will offer the same IP address to a host when the host requests an IP address85．The ( )field permits Ethernet to multiplex network-layer protocols.A preambleB typeC CRCD destination MAC address86．For 10BaseT, the maximum length of the connection between an adapter and the hub is ( ) meters.A 50B 100C 200D 50087．An entry in the switch table contains the following information excepts for ( )A the MAC address of a nodeB the switch interface that leads towards the nodeC the time at which the entry for the node was placed in the tableD the IP address of a node88．Consider the 4-bit generator , G is 1001, and suppose that D has the value 101110000. What is the value of R?89．Consider the following graph of the network. Suppose Host A will send a datagram to Host B, Host A run OICQ on port 4000, Host B run OICQ on port 8000. All of ARP tables are up to date. Enumerate all the steps when message “Hello” is sent from host A to host B.。
计算机网络技术第五章知识点计算机网络技术的第五章通常涵盖了网络层的相关重要知识。
网络层作为计算机网络体系结构中的关键层次，承担着数据分组的路由选择和转发等核心任务。
网络层的主要功能之一是路由选择。
简单来说，就是确定数据分组从源节点到目的节点的最佳路径。
这就好比我们在出行时需要规划一条最优的路线，网络中的数据分组也需要找到一条最快捷、最可靠的路径来传输。
为了实现路由选择，网络层使用了各种各样的路由算法。
其中，距离矢量路由算法和链路状态路由算法是比较常见的两种。
距离矢量路由算法通过相邻路由器之间交换路由信息来更新路由表。
每个路由器会告诉邻居自己到各个目的地的距离（通常用跳数来衡量）。
然而，这种算法可能会存在计数到无穷大的问题，导致路由环路的出现。
链路状态路由算法则相对更加复杂和准确。
每个路由器需要了解整个网络的拓扑结构和链路状态信息，然后通过计算最短路径来构建路由表。
这种算法能够有效地避免路由环路，但计算量较大，对路由器的性能要求较高。
除了路由选择，网络层还负责数据分组的转发。
当数据分组到达路由器时，路由器会根据路由表中的信息将其转发到下一个合适的节点。
转发的过程通常是基于目的地址进行的。
网络地址转换（NAT）也是网络层的一个重要概念。
在私有网络中，使用的是私有 IP 地址，这些地址不能在公共网络中直接使用。
NAT 技术可以将私有 IP 地址转换为合法的公共 IP 地址，从而实现私有网络与公共网络的通信。
IPv4 是当前广泛使用的网络层协议，但由于其地址空间有限，IPv6 逐渐得到推广。
IPv6 具有更大的地址空间、更好的安全性和扩展性。
在网络层中，还涉及到一些控制和管理机制，比如拥塞控制。
当网络中的数据流量过大，导致网络拥塞时，需要采取相应的措施来缓解拥塞，保证网络的正常运行。
常见的拥塞控制方法包括慢开始、拥塞避免、快重传和快恢复等。
另外，网络层的服务质量（QoS）也是一个重要的方面。
不同的应用对网络性能有不同的要求，比如实时性要求较高的语音和视频通信需要较低的延迟和抖动，而文件传输则对可靠性要求较高。
