Chapter 7 Packet_Switching_networks
计算机网络(第四版)课后习题(英文)+习题答案(中英文)
川大林峰计网第一次作业
I. Multiple Choice1.1In the following options, which does not define in protocol? ( D )A the format of messages exchanged between two or more communicating entitiesB theorder of messages exchanged between two or more communicating entities C the actions taken on the transmission of a message or other event D the transmission signals are digital signals or analog signals1.2In the following options, which is defined in protocol? ( A )A the actions taken on the transmission and/or receipt of a message or other eventB theobjects exchanged between communicating entities C the content in the exchanged messages D the location of the hosts1.3 Which of the following nodes belongs to the network core? ( C )A. a Web ServerB. a Host with Win2003 ServerC. a Router with NAT serviceD. a Supernode on Skype Network1.4 In the Internet, the equivalent concept to end systems is ( A ). A hostsB serversC clientsD routers1.5 In the Internet, end systems are connected together by ( C ). A copper wireB coaxial cableC communication linksD fiber optics1.6 End systems access to the Internet through its ( C ). A modemsB protocolsC ISPD sockets1.7 In the following options, which belongs to the network core? ( B ) A end systemsB routersC clientsD servers1.8 End systems, packet switches, and other pieces of the Internet, run ( D ) that control the sending and receiving of information within the Internet. A programs B processes C applications D protocols1.9 The protocols of various layers are called ( A ). A the protocol stack B TCP/IP C ISP D network protocol1.10 In the OSI reference model, the upper layers of the OSI model are, in correct order (D)a) Session, application, presentation b) Session, presentation, application c) Session, application, presentation, physical d) Application, presentation, session1.11 The lower layers of the OSI model are, in correct order( D )a) physical, system, network, logical b) physical, logical, network, system c) physical, transport, network, data link d) physical, data link, network, transport1.12 Which of the following protocol layers is not explicitly part of the Internet Protocol Stack? ___B______ A. application layer B. session layer C. data link layer D. transport layer1.13 The 5-PDU is called__D_ A. message B. segment C. datagram D. frame1.14 Transport-layer packets are called: BA. messageB. segmentC. datagramD. frame1.15 The units of data exchanged by a link-layer protocol are called ( A ). A FramesB SegmentsC DatagramsD bit streams1.16 There are two fundamental approaches to building a network core, ( B ) and packet switching. A electrical current switching B circuit switching C data switching D message switching1.17 There are two classes of packet-switched networks: ( B ) networks and virtualcircuit networks. A datagramB circuit-switchedC televisionD telephone1.18 ( A ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM1.19 In ( C ) networks, the resources needed along a path to provide for communication between the end system are reserved for the duration of the communication session. A packet-switched B data-switched C circuit-switched D message-switched1.20 In ( A ) networks, the resources are not reserved; a session’s messages use the resources on demand, and as a consequence, may have to wait for access to communication link. A packet-switched B data-switched C circuit-switched D message-switched1.21 Which of the following option belongs to the circuit-switched networks? ( D ) A FDMB TDMC VC networksD both A and B1.22 In a circuit-switched network, if each link has n circuits, for each link used by the end-to-end connection, the connection gets ( A ) of the link’s bandwidth for the duration of the connection. A a fraction 1/n B all C 1/2D n times1.23 For ( C ), the transmission rate of a circuit is equal to the frame rate multiplied by the number of bits in a slot. A CDMA B packet-switched network C TDM D FDM1.24 The network that forwards packets according to host destination addresses is called ( D ) network. A circuit-switched B packet-switched C virtual-circuit D datagram1.25 The time required to propagate from the beginning of the link to the next router is ( C ). A queuing delay B processing delay C propagation delay D transmission delay1.26 Processing delay does not include the time to ( B ). A examine the packet’s header B wait to transmit the packet onto the link C determine where to direct the packet D check bit-error in the packet1.27 In the following four descriptions, which one is correct? ( C )A The traffic intensity must be greater than 1.B The fraction of lost packets increases as the traffic intensity decreases.C If the traffic intensity is close to zero, the average queuing delay will be close to zero.D If the traffic intensity is close to one, the average queuing delay will be close to one.1.28 Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( B ), A LR／a B La／R C Ra／L D LR／a1.29 and it should no greater than ( B ). A 2 B 1 C 0D -11.30 Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2, respectively. Assuming that the switch uses store-and-forward packet switching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing delay, propagation delay, and processing delay.) ( A ) A L/R1＋L/R2 B L/R1 C L/R2 D none of the above1.31 We are sending a 30 Mbit MP3 file from a source host to a destination host. Suppose there is only one link between source and destination and the link has a transmission rate of 10 Mbps. Assume that the propagation speed is 2 * 108 meters/sec, and the distance between source and destination is 10,000 km. Also suppose that message switching is used, with the message consisting of the entire MP3 file. How many bits will the source have transmitted when the first bit arrives at the destination? CA. 1 bitB. 30,000,000 bitsC. 500,000 bitsD. none of the above1.32 Access networks can be loosely classified into three categories: residential access, company access and ( B ) access. A cabled B wireless C campus D city area1.33 The following technologies may be used for residential access, except DA. HFCB. DSLC. Dial-up modemD. FDDI1.34 Which kind of media is not a guided media? ( D ) A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channelII. True or False1.35 There is no network congestion in a circuit switching network.False1.36 Consider an application that transmits data at a steady rate, and once this application starts, it will stay on for a relatively long period of time. According to the characteristic, a packet-switched network would be more appropriate for this application than a circuit-switched network.FalseIII. Please Answer Following Questions Briefly1.37 How many layers are there in the Internet protocol stack? What are they? What are the principal responsibilities of each of these layers?5层。
商务英语阅读Unit 7-叶兴国ppt课件
UNIT 7
9. Loan word外来词构词法: 如：
karoshi (日语) ：过劳死；
westpolitik(德语) ：东欧国家的西方政策等。
10. Coinage创新式构词法 : 如：
1) 政治领域：Ground Zero世贸废墟, the global coalition against terror全球反
READING SKILLS:
Business English: A Reading Course
INTRODUCE THE BASIC INFORMATION ABOUT BUSINESS ENGLISH READING
UNIT 7
6. Onomatopoeia拟声词构词法:
1) 直接~: 音与义基本吻合，能直接产生音义之间的互相联想，使 用频率高。
?人类基因组数据库genomedatabase该数据库1990年初建于美国霍普金斯大学是一个专门汇集存储人类基因组数据的数据库其中包括了全球范围内致力于人类dna结构和100000种人类基因序列研究的分析成果
Business English: A Reading Course
UNIT 7
2014.11
Unit 5: Affixation; Compounding; Unit 6: Conversion; Blending; Shortening; Unit 7: Onomatopoeia; Back formation; Formation of nonce words; Loan
word; Coinage
恐联盟 political pluralism政治多元化, bushism布什执行的强硬政策等。
2) 经济领域：G-7 nations 7国集团, cyclic/bubble economy循环经济, bubble
电路交换和分组交换（Circuitswitchingandpacketswitching）
电路交换和分组交换（Circuit switching and packet switching）Circuit switching and packet switchingCircuit switching technology is rarely used in data service networks, mainly because of the low efficiency and reliability of its resource utilization. Packet switching technology improves the efficiency of resource utilization by means of statistical multiplexing. Moreover, when line faults occur, packet switching technology can improve reliability by re routing retransmission. But the reality is that many of the line resources due to the lack of exchange ability is not used, the utilization rate of line resource use is often less than ten percent a year on average, the router downtime is less than 5 seconds, the probability of failure is very small. Therefore, the reasons for today's choice of switching technology do not make sense.On the other hand, packet switching is non connection oriented, and has inherent defects for some real-time transactions. Although there are a series of mitigation measures, such as resource reservation, it is not enough to solve the fundamental problem. Therefore, these business QoS problems are more complex. While circuit switching technology is connection oriented, it is suitable for real-time business, and its QoS problem is much simpler. At the same time, compared with packet switching technology, circuit switching technology is simple, inexpensive and easy to implement with hardware. And because it does not require buffers, and optical buffer technology seems to be far away, so it is easier to integrate with optical technology. Of course, the problem of traffic granularity mismatch between users of circuit switching technology and WDMis still to be solved. If you leave the existing facilities from scratch, it is believed that the possibility of choosing circuit switching technology is much greater. Here is an example that compares circuit switching techniques with packet switching techniques. Suppose a server connects with 100 users via a 1Mbit/s link, and the result is shown in table 1.Table 1 connection result table for 1Mbit/s link with 100 users:Circuit switched packet switchingBandwidth 1Mbit/s 10Kbit/sThe mean delay is 50s 100sThe maximum delay is 100s 100sCircuit switchingEach telephone is connected to the switch, and the switch uses the exchange method so that telephone users can communicate conveniently. Over the past more than 100 years, telephone switches have been switched over and over again, but circuit switching has always been the mode of exchange. When the number of telephones increases, the switches connected with each other are used to complete the exchange of the whole network. Note that this kind of switch uses circuit switching, and later packet switching uses the same telecommunications network, but different types of switches (of course, protocols are different).From the point of view of the distribution of communication resources, "switching" means dynamically allocating the resources of the transmission lines in some way.Before using the circuit switched call, dial the number to establish a connection: when dialing signaling through many switches to the called user connected to the switch, the switch to the telephone ringing of the user; the called user off hook and hook signals sent back to the calling user switches connected after the call is completed, then from the end to the caller on the establishment of a called terminal connection. Call process. After the call has been hung up, the hang up signaling tells these switches that the switch releases the physical path. This must be done through the three steps of "connection, communication, release, connection", called connection oriented. Circuit switching must be connection oriented.User to switch between called user line, dedicated to telephone users. Many users sharing between switches, called a relay line, with a large number of words, a word is on the phone users only take the road, all the time in the call, the two user calls always occupied fixed end to end transmission bandwidth.The mode of exchange for the purpose of circuit connection is circuit switching. In telephone networks, circuit switching is adopted. We can make a phone call to experience this mode of exchange. When you make a phone call, first pick up your phone and dial. After dialing, the switch will know who to talk to and who will establish the connection. When one party hangs up, the switch disconnects the lines,Get ready for each other to start a new call. Therefore, we can understand that the action of circuit switching is to establish (link) circuit in communication, and to remove (disconnect) circuit when communication is complete. As for communication, the contents of both sides are not related to the switching system.For example, suppose we have A, B, two cities, each city has a switch, and there are one thousand users, and two switches are connected by 100 trunks. So, if we say, "build a circuit between two users in A city", we mean connecting two user lines through the switches of A city. But when we say: set up a circuit between a user and a user of the B city of A, we refer to is by the subscriber line in A city by city of A connected to the switch between A and B, a trunk line, in the city of B switches connected to the subscriber line in B City the. Because of economic reasons, the relay lines are always much less than the subscriber lines and are shared by all users. Then, when we occupy a relay line, even if we do not transmit information, others can not use it, which is the most important drawback of circuit switching.In telephone communications, because the two sides of the speech are always talking and one is listening, the circuit idle time accounts for about 50%.What mechanism does the first generation of computer networks use?Circuit switchingCircuit switching is the process of communication to maintain the actual electronic circuit (physical circuit), after the establishment of this electronic circuit, the user always accounts forFixed transmission bandwidth from sender to receiverWhat are the disadvantages of the circuit switching mechanism?According to the principle of circuit switching, circuit switching will take up fixed bandwidth, which limits the traffic and the number of connections on the networkCircuit switching is often compared to packet switching. The main difference is that the communication lines of packet switching are not dedicated to the transmission of information between source and destination. The use of circuit switching is an ideal choice when data are required to be transmitted in sequence and at a constant rate. Therefore, when a real-time data is transmitted, such as audio and video, or when the quality of service (QOS) requirement is high, a circuit switched network is usually used. Packet switching is more efficient in data transmission, preventing delays and jitter in transport processes such as e-mail information and Web pagesPacket switching technology is in the development of computer technology to a certain extent, people in addition to direct telephone communication, through the realization of communication between computer and computer and computer terminal in the transmission line, the quality is not high, thenetwork technology is a single case, a switching technology came into being.Packet switching, also called packet switching, divides the data transmitted by the user into a certain length, each of which is called a packet. In front of each packet and a packet header, to indicate that the packet sent to any address, followed by the address of the packet switch according to each sign, they will be forwarded to the destination, a process called packet switching. Packet switched communications networks are called packet switched networks. In the light of the history of switching technology, data exchange has undergone the development of circuit switching, message switching, packet switching and integrated services digital exchange. Packet switching is essentially developed on the basis of store and forward. It has the advantages of circuit switching and message switching. Packet switching on-line adopts dynamic multiplexing technology to transfer data into many small segments according to a certain length. After each grouping is identified, a dynamic multiplexing technique is used on a physical line to deliver multiple data packets simultaneously. The data originating from the user is temporarily stored in the memory of the switch, and then forwarded in the network. At the receiving end, the packet header is removed, and the data fields are reassembled in sequence into full packets. Compared with circuit switching, packet switching has higher utilization ratio, less transmission delay and better interaction.In packet switching mode,Because packet switching can be carried out in packet mode, it is easy to implement inter - terminal communication at different rates and different procedures after switching processing. Packet switching is mainly characterized by:* the utilization of the line is high: packet switching carries out multiplexing of channels in the form of virtual circuits, realizes resource sharing, provides multiple logical channels on a physical line, and greatly improves the utilization of the line. Significantly reduce transmission costs.* different terminal can communicate with each other: the packet network provides the standard interface to the users in the X.25 protocol, the data packet in the network as a unit to store and forward, so that different rate of terminal protocol conversion function devices of different protocols are provided through network to achieve mutual communication.* the reliability of information transmission is high. When each packet is transmitted in the network, it uses the function of error check and retransmission between the node switches so that the bit error rate transmitted in the network is greatly reduced. Moreover, when the network fails, the routing mechanism in the network will automatically select a new route for the packet to avoid the point of failure and will not cause communication interruption.* packet multiplex communication: since each packet contains control information, a packet terminal can communicate with several user terminals at the same time, and send the same information to different users.* billing has nothing to do with transmission distance: network billing is long on time, information is charged, and it has nothing to do with the transmission distance. It is especially suitable for users who are not real-time and have little traffic.Packet switching network structure is usually composed of packet switching, network management center, remote concentrator, sub assembly and disassembly equipment, packet terminal / non packet terminal and transmission line and other basic equipment. Packet switching function:Provide basic services of the network: switching virtual circuits and permanent virtual circuits and other supplementary services, such as closed and user groups, network user identification, etc.. When communicating between end - to - end computers, routing and traffic control are performed. Can provide a variety of communication procedures, data forwarding, maintenance operations, fault diagnosis, billing and some network statistics.There is a user access mode:Dial-up network access: users use X.28 or X.32 procedures, and use a modem through a public telephone network (PSTN) to connect to a packet switched network.Private line users can rent telephone analog lines or digital data lines and adopt X.28 or X.25 rules. Easy access to CHINAPAC. CHINAPAC provides two basic business functions to users:Switched virtual circuit - a temporary logical connection between two users.Permanent virtual circuit - a permanent logical connection between two users. Once the user has turned on the machine, a permanent virtual circuit is automatically established.There is no link between the two host computers as a unique circuit connection. The source host will group the whole message one by one, while each of the host messages will be grouped togetherEach packet adds sufficient protocol information to enable them to be routed to the correct target hostWhat are the advantages of packet switching versus circuit switching?The messages sent by the packets do not take up fixed bandwidth and allow more connections to be built on the line。
《计算机网络》_第7版_谢希仁_复习知识点
第一章概述1.21世纪的一些最重要的特征就是数字化、网络化和信息化，它是一个以网络为核心的信息时代。
2.Internet是由数量极大的各种计算机网络互连起来的。
3.互联网的两个重要基本特点，即连通性和共享。
4.互联网已经成为世界上最大的计算机网络。
5.以小写字母i开始的internet（互连网）是一个通用名词，它泛指由多个计算机网络互连而成的计算机网络。
以大写字母I开始的Internet（互联网，或因特网）则是一个专用名词，它指当前全球最大的、开放的、由众多网络相互连接而成的特定互连网，它采用TCP/IP协议族作为通信的规则，且其前身是美国的ARPANET。
6.所谓“上网”就是指“（通过某ISP获得的IP地址）接入到互联网”。
7.客户（client）和服务器（server）都是指通信中所涉及的两个应用进程。
客户程序：必须知道服务器程序的地址，不需要特殊的硬件和很复杂的操作系统。
服务器程序：可同时处理多个远地或本地客户的请求，系统启动后即自动调用并一直不断地运行着，被动地等待并接受来自各地的客户的通信请求，不需要知道客户程序的地址，一般需要有强大的硬件和高级的操作系统支持。
8.路由器（router）是实现分组交换（packet switching）的关键构件，其任务是转发收到的分组，这是网络核心部分最重要的功能。
9.分组交换的优点：高效-动态分配传输带宽，逐段占用通信链路，灵活-为每一个分组独立地选择最合适的转发路由，迅速-以分组作为传送单位，可以不先建立连接就能向其他主机发送分组，可靠-保证可靠性的网络协议；分布式多路由的分组交换网。
10.计算机网络主要是由一些通用的、可编程的硬件互连而成的，而这些硬件并非专门用来实现某一特定的目的（例如，传送数据或视频信号）。
这些可编程的硬件能够用来传送多种不同类型的数据，并能支持广泛的和日益增长的应用。
11.速率的单位是bit/s（比特每秒）（或b/s，有时也写为bps，即bit per second）。
网络基础-OSI网络七层参考模型
总结（续）
– 传输层可在发送主机系统上对数据进行分段， 在接收主机系统上将数据段重组为数据流。
– 会话层可建立、管理和终止两台通信主机间 的会话。
– 表示层可确保某一系统的应用层所发送的信 息可被另一系统的应用层读取。
– 应用层可为用户的应用程序（例如电子邮件、 文件传输和终端仿真）提供网络服务。
➢网络体系结构解决异质性问题采用的是 分层方法。——把复杂的网络互联问题 划分为若干个较小的、单一的问题，在 不同层面上予以解决。就像编程时把问题分解
层次结构方法要解决的问题
1.网络应该具有哪些层次？每一层的功能是什么？ （分层与功能）。
2.各层之间的关系是怎样的？它们如何进行交互？ （服务与接口）。
总结（续）
– 通过网络发送的信息称为数据或数据包。如 果一台计算机要向另一台计算机发送数据， 则必须首先执行被称为封装的过程以将数据 打包。
– 当远程设备接收到比特序列时，远程设备的 物理层便会将这些比特序列传送到数据链路 层进行处理。该过程称为解封。
总结（续）
– TCP/IP 是目前使用最广泛的协议，其原因众多， 例如灵活的编址方案、适用于大多数操作系统 和平台、具有许多工具和实用程序，以及需使 用它来连接 Internet。
以不同国籍的人进行信息交流为例。(见下页图)
对等通信示例：中德教师之间的对话
中国 教师
翻译
秘书
“你好” “Hello” 传真
对交谈内容的共识
P3
用英语对话
P2
使用传真通信
P1
“Hallo” “Hello” 传真
德国 教师
翻译
秘书
物理通信线路
问题： 中国教师与德国教师之间、翻译之间，他们是在直接通信吗？ 翻译、秘书各向谁提供什么样的服务？ 中德教师、翻译各使用谁提供的什么服务？
计算机网络简介
住宅接入：电缆网
cable headend
…
cable splitter modem
V I D E O 1
V I D E O 2
V I D E O 3
V I D E O 4
V I D E O 5
V I D E O 6
D A T A 7
D A T A 8
C O N T R O L 9
Channels
1-2
1.1 What is the Internet?
将从以下两个角度描述因特网是什么:
因特网的具体构成 因特网的功能
Introduction
1-3
1.1.1 因特网的具体构成
桌面机 服务器 笔记本
• 终端： • 称 主机（host）或端系 统（ end system） • 运行应用程序
R bps
R bps
destination
将一个条
链路的总耗时是多少？
将一个分组从源发送到目 的，总耗时 = 2 L/R （不 考虑信号传播时间） 3个分组从源终端发送到目 的终端，总耗时=？
Institutional network
1.1.2 因特网的功能
因特网定义二：
因特网是为分布式应用提供 通信服务的基础设施
服务接口： 电话系统：拨号，振铃
邮政系统：写有通信地址的 信封，邮筒，信箱
因特网提供给应用程序的服
务接口：
一组用于在因特网上发送和 接收数据的应用编程接口API
主机将要传输的数据划
分并组装成一系列分组
交换：在传输路径上，
交换设备从一条链路上 接收分组，然后将其发 送到另一条链路上
计算机网络(第六版)课后习题答案
《计算机网络》课后习题答案第一章概述1-1 计算机网络向用户可以提供哪些服务？答：计算机网络向用户提供的最重要的功能有两个，连通性和共享。
1-3 试从多个方面比较电路交换、报文交换和分组交换的主要优缺点。
答：（1）电路交换电路交换就是计算机终端之间通信时，一方发起呼叫，独占一条物理线路。
当交换机完成接续，对方收到发起端的信号，双方即可进行通信。
在整个通信过程中双方一直占用该电路。
它的特点是实时性强，时延小，交换设备成本较低。
但同时也带来线路利用率低，电路接续时间长，通信效率低，不同类型终端用户之间不能通信等缺点。
电路交换比较适用于信息量大、长报文，经常使用的固定用户之间的通信。
（2）报文交换将用户的报文存储在交换机的存储器中。
当所需要的输出电路空闲时，再将该报文发向接收交换机或终端，它以“存储——转发”方式在网内传输数据。
报文交换的优点是中继电路利用率高，可以多个用户同时在一条线路上传送，可实现不同速率、不同规程的终端间互通。
但它的缺点也是显而易见的。
以报文为单位进行存储转发，网络传输时延大，且占用大量的交换机内存和外存，不能满足对实时性要求高的用户。
报文交换适用于传输的报文较短、实时性要求较低的网络用户之间的通信，如公用电报网。
（3）分组交换分组交换实质上是在“存储——转发”基础上发展起来的。
它兼有电路交换和报文交换的优点。
分组交换在线路上采用动态复用技术传送按一定长度分割为许多小段的数据——分组。
每个分组标识后，在一条物理线路上采用动态复用的技术，同时传送多个数据分组。
把来自用户发端的数据暂存在交换机的存储器内，接着在网内转发。
到达接收端，再去掉分组头将各数据字段按顺序重新装配成完整的报文。
分组交换比电路交换的电路利用率高，比报文交换的传输时延小，交互性好。
1-5 因特网的发展大致分为哪几个阶段？请指出这几个阶段最主要的特点。
答：第一阶段是从单个网络ARPANRET 向互联网发展的过程。
最初的分组交换网ARPANET 只是一个单个的分组交换网，所有要连接在ARPANET 上的主机都直接与就近的结点交换机相连。
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10 very lightly loaded user 10 lightly loaded users 20 lightly loaded users 40 lightly loaded users
100 lightly loaded users 100 0.1 18 5.5 As N increases, the total traffic is more predictable. So the outgoing capacity can be chosen closer to the mean (relative to N).
Chapter 7 Packet-Switching Networks
Network Services and Internal Network Operation Packet Network Topology Datagrams and Virtual Circuits Routing in Packet Networks Shortest Path Routing
Internet service provider
Border routers
Campus Network
Autonomous system or domain
Border routers Interdomain level
Intradomain level
s s s
LAN
network administered by single organization
R
S R
s s s s s s s
High-speed Only outgoing campus s packets leave backbone net LAN through connects dept router routers e.g., GigE or ATM
13
Connecting to Internet Service Provider
9
Oversubscription
Access Multiplexer
•••
•••
r r r Nr
nc
Nc
N subscribers connected @ c bps to mux Each subscriber active r/c of time Mux has C=nc bps to network Oversubscription rate: N/n Find n so that at most 1% overflow probability
10
Home LANs
WiFi Ethernet
Home Router
To packet network
Home Router
LAN Access using Ethernet or WiFi (IEEE 802.11) Private IP addresses in Home (192.168.x.x) using Network Address Translation (NAT) Single global IP address from ISP issued using Dynamic Host Configuration Protocol (DHCP)
1
Chapter 7 Packet-Switching Networks
Network Services and Internal Network Operation
2
Network Layer
Network Layer: the most complex layer
Requires the coordinated actions of multiple, geographically distributed network elements (switches & routers) Must be able to deal with very large scales
14
Internet Backbone
National Service Provider A
National Service Provider B
NAP
National Service Provider C Private peering
NAP
Network Access Points: set up during original commercialization of Internet to facilitate exchange of traffic Private Peering Points: two-party inter-ISP agreements to exchange traffic
12
Campus Network
To Internet or wide area network
Backbone
Servers have redundant connectivity to backbone
Organization Servers
s s
R
Gateway
R S S R R
Departmental Server s
Network Layer Functions
Essential Routing: mechanisms for determining the set of best paths for routing packets requires the collaboration of network elements Forwarding: transfer of packets from NE inputs to outputs Priority & Scheduling: determining order of packet transmission in each NE Optional: congestion control, segmentation & reassembly, security
15
(a)
National Service Provider A
National Service Provider B
NAP
National Service Provider C
Private peering
NAP
(b)
NAP
Route
Server LAN
RA RB
RC
16
Key Role of Routing
4
Network Service
Messages
Transport layer Network service Network layer Network layer Data link layer Physical layer Network layer Data link layer Physical layer Network layer Data link layer Physical layer
How to get packet from here to there? Decentralized nature of Internet makes routing a major challenge
Interior gateway protocols (IGPs) are used to determine routes within a domain Exterior gateway protocols (EGPs) are used to determine routes across domains Routes must be consistent & produce stable flows Hierarchical structure of IP addresses essential to keeping size of routing tables manageable
6
Chapter 7 Packet-Switching Networks
Packet Network Topology
7
End-to-End Packet Network
Packet networks are very different than telephone networks, in that
11
LAN Concentration
Switch / Router
LAN Hubs and switches in the access network also aggregate packet streams that flows into switches and ros
Transport layer Network service
End system Physical α
layer
Data link layer
End system β
Network layer can offer a variety of services to transport layer Connection-oriented service or connectionless service 5 Best-effort or delay/loss guarantees
User demand can undergo dramatic change
Internet structure highly decentralized
8
Access Multiplexing