1、1,Data Communications and Networking,Chapter 1Data Communications, Data Networks, and the InternetReading:Book Chapter 1Data and Computer Communications, 8th editionBy William Stallings,2,Outline,Section 1: Data Communications and Networking for Todays EnterpriseSection 2: A Communications ModelSect
2、ion 3: Data CommunicationsSection 4: NetworksSection 5: The InternetSummary: Key PointsAppendix: History of Communications,3,Section 1,Data Communications and Networking for Todays Enterprise,4,What are the trends?,Three forces are driving the evolution of data communications and networkingGrowth of
3、 communication trafficVoice traffictelephoneData trafficInternet access, video conferencingChallenges (to the network service providers):how to maximize the capacity and minimize the cost?Development of new servicesRefer to the figure on the next pageAdvances in technologyFaster and cheaper computin
4、g and communicationsNetworks are more intelligent: quality of service (QoS)Internet, Web, intranets, extranets, etc.Pervasive computing/ubiquitous computing,5,Figure 1: Service versus Throughput Rates,6,Case Studies:,What networking services do we use today?Phone service (mainly for voice)Internet s
5、ervice (mainly for data)Example of Mobile Phone Service: THREE.comhttp:/.hk/website/template?pageid=35200&lang=chiExample of Broadband Internet Access: HKBNhttp:/.hk/bb1000/offer_no_contract.htmlQuestionsWhy mobile phone service is charged based on time (i.e., number of minutes)?why Internet access
6、service is charged based on the data rate (i.e., number of MB/s)?,7,How is our life without Internet?,Time: Dec. 26, 2006Event: An earthquake at TaiwanConsequence:香港新报28日头条报道称，台湾大地震除了在当地造成伤亡，亦令互联网世界出现前所未有的大灾难。多条经台湾传送互联网数据的海底电缆在地震中受破坏，由于台湾是香港以至东南亚互联网用户接驳至外地的主要“出口”，电缆受损令香港等多个地区的互联网一度“与世隔绝”，香港网民未能登入外国网
7、站，电邮服务亦几乎全部中断，长途电话及国际漫游服务同受影响。,8,(Cont.),华声报旧金山消息：12月26日台湾的一场强震不仅给台湾百姓造成了严重的损失，也给在美华人带来了程度不同的经济影响。由于地震毁掉了6条海底电缆，导致中美之间的网络中断，南加华商生意遭受挫折抱怨连连。Case 1:吴老板说，“在美国雇一个员工的钱在中国可以雇10个，网上销售为我带来了无限商机。”可是26日他突然发现上不去网了。“网络销售占本公司全部销售额的一半，如果要两个星期才能修复海底光缆的话，仅网上eBay销售这一块我的损失就超过28万元，加上国内网站的管理费和员工工资等，这场地震给我造成的直接损失至少在30万元
8、以上”。Case 2:工业市华裔商人石小姐在经营运输公司之余，还在香港做些股票生意，27日她发现无法登陆香港股市网站，当得知是地震的原因时，她心急如焚地表示，“完了，这几天上不了网，我的几百万股票恐怕凶多吉少。”,9,What lessons can we learn?,Internet is an important infrastructure of our society.Reliability is a critical factor, especially for businesses that rely on networking technology.Question: If y
9、ou are a network manager for a company, how will you increase the reliability of your companys network connection?,10,Section 2,A Communications Model,11,Human Communications,A transmitter: mouthA receiver: earThe media: airQuestion: Can you talk at outer space?The protocol: a common human languageQ
10、uestion: why do we learn English?,12,A Communications Model,What is the purpose of communications? Exchange of information between two partiesKey elementsSource: Generates data to be transmitted. E.g., telephones, PCs.Transmitter: A transmitter transforms and encodes the information in such a way as
11、 to produce electromagnetic signals that can be transmitted across some sort of transmission system.Transmission SystemIt can be a single transmission line or a complex network connecting source and destination.Destination: Takes incoming data from the receiverReceiver: The receiver accepts the sign
12、al from the transmission system and converts it into a form that can be handled by the destination device.,13,Simplified Communications Model,14,Section 3,Data Communications,15,Simplified Data Communications Model,Assume the source and destination are PCs. The source wishes to send a message m to t
13、he destination.,16,Transmission of Information,One basic choice facing a business user is the selection of transmission medium.Within the business premiseCompletely up to the businessLong-distance communicationsUp to the long-distance carrierNew technologiesOptical fiber transmissionWireless transmi
14、ssionHow to improve the efficiency of the use of network facilities?Multiplexing and compression,17,Section 4,Networks,18,Why do we need a network?,Point to point communication is not always practicalDevices are too far apartLarge set of devices would need impractical number of connections,Telegraph
15、 wires in late 19th century,19,Networking,Solution is to use a communications network,A telephone switch in 1960s,20,Todays network switches,Cisco Catalyst 6500 Series Switches,21,At Ancient Time,How to achieve long-distance communications?Solution 1Signal firesExampleSee the movie segment in “The L
16、ord Of The Rings Return Of The King” directed by Peter Jackson.Solution 2Messengers, horses, post houses (驛站)How efficient is it?56 days from 北京 to 廣州In both solutions, the concept of “relay” is very important, and it forms the basic principle of todays Internet.,22,Wide Area Networks,Cover a large
17、geographical areaConsists of a set of interconnected switching nodesAlternative technologiesI. Circuit switchingTelephone networkII. Packet switchingX.25: popular in 1980sFrame relay: to replace X.25Asynchronous Transfer Mode (ATM): an evolution from frame relayInternet: the dominant global network
18、today,23,(I) Circuit Switching,Dedicated communications path established for the duration of the conversationThree steps:Setup the circuit: allocate dedicated resources.Transmit the data: utilize resources.Terminate the circuit: release resources.E.g. telephone networkNow, can you answer the questio
19、n on Slide 6?,24,(II) Packet Switching,Data are sent out in a sequence of small chunks, called packets.Each Packet is passed through the network from node to node along some path leading from source to destinationAt each node, the entire packet is received, stored, and then transmitted to the next n
20、odeStore-and-forward: bufferingWhats the impact?,25,Local Area Networks,Smaller scopeOffice, Building, CampusUsually owned by the same organization that owns the attached devicesInternal data rates are high10Mbps 100Mbps 1Gbps 10GbpsWireless LANs become more and more popularData rates of wireless LA
21、Ns are increasing: 11Mbps 54Mbps hundreds of Mbps,26,Section 5,The Internet,27,Internet Elements,The purpose of the Internet is to interconnect end systems, called hostsSuch as PCs, servers, notebooks, PDAs, smart phones, etc.Most hosts that use the Internet are connected to a network, such as a LAN
22、 or a WANNetworks are in turn connected by routers. Each router attaches to two or more networks.A host may send data to another host anywhere on the Internet:The source host breaks the data into a sequence of packets, called IP packets, or IP datagrams.Each packet includes the unique numeric addres
23、ses of the source host and destination host, called IP addresses.Based on the destination IP address, each packet travels through a series of routers and networks from source to destination.Each router, upon receiving an IP packet, makes a routing decision and forwards the packet along its way to th
24、e destination.,28,Internet Elements,29,Internet Architecture,Todays Internet is made up of thousands of overlapping hierarchical networks.Individual hosts and LANs are connected to an Internet Service Provider (ISP) through a Point of Presence (POP).Customer Premises Equipment (CPE): the communicati
25、ons equipment located onsite with the host, such as the modem.Different levels of ISPsLocal ISP, Regional ISP, Backbone ISPBackbone ISPs may be connected through the Network Access Point (NAP).,30,Internet Architecture,31,KEY POINTS,Data communications deals with the transmission of signals in a rel
26、iable and efficient manner. Topics covered include signal transmission, transmission media, signal encoding, interfacing, and data link control.Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices. This field is generally div
27、ided into the topics of local area networks (LANs) and wide area networks (WANs).,32,Appendix:A brief history of communications,1830-1840s, Samuel Morse Morse code Telegraph1850sEuropean and US are connected by submarine telegraphy cables. 1870s, Alexander BellTelephoneBell labs was setup in 1925, t
28、hree years after Bells death.1956US and UK are connected by telephone cables.Question: why is it more difficult to make long-distance telephones work, as compared with long-distance telegraph?,33,Morse Code,34,(Cont.),1960sDigital data communications occurredLate 1960s and early 1970sARPANET: the fi
29、rst computer network, the beginning of the InternetLate 1960s, K. C. KaoOptical FiberK.C. Kao: Father of the fiberServed as the president of CUHK from 1987 to 1996.Nobel prize in Physics 2009http:/ transmission and switching begins1973, Robert MetcalfeEthernetFounded 3Com Corp. in 19791981Cellular mobile telephone1991, Tim Berners-LeeWorld-Wide WebExplosion of Internet,Charles Kuen Kao 高錕,
