北京邮电大学思科网络技术学院1http:/cisco.bupt.edu.cnCommunicating over the NetworkNetwork Fundamentals Chapter 22北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cnObjectivesDescribe the structure of a network, including the devices and media that are necessary for successful communications.Explain the function of protocols in network communications.Explain the advantages of using a layered model to describe network functionality.Describe the role of each layer in two recognized network models: The TCP/IP model and the OSI model.Describe the importance of addressing and naming schemes in network communications.3北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cnObjectives描述网络的结构，包括成功通信所需的设备和介质。说明协议在网络通信中的功能。说明使用分层模型来描述网络功能的优点。描述以下两种公认网络模型中每一层的作用：TCP/IP 模型和 OSI 模型。说明编址和命名方案在网络通信中的重要性。4北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cnContext Index2.1 The Platform for Communications2.2 LANs, WANs, and Internetworks2.3 Protocols 2.4 Using Layered Models2.5 Network Addressing北京邮电大学思科网络技术学院5http:/cisco.bupt.edu.cn2.1 The Platform for Communications通信平台通信平台6北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.1 The Elements of CommunicationData or information networks capable of carrying many different types of communications3 common elements of communicationmessage source （消息来源）the channel （传输通道）message destination（消息的目的）7北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.2 Communicating the MessagesSegmentation - breaking communication into pieces.8北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.2 Communicating the MessagesMultiplexing interleaving the pieces as they traverse the media.9北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.2 Communicating the MessagesThe downside to using segmentation and multiplexing to transmit messages across a network is the level of complexity that is added to the process. （分段和复用增加了网络的复杂性。 ）10北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.3 Components of the Network(网络的组成网络的组成)Devices and media are the physical elements or hardware of the network.11北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.3 Components of the Network (网络的组成网络的组成)Services and processes are the communication programs, called software, that run on the networked devices.12北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.4 End Devices and their Role on the NetworkSome examples of end devices are:Computers (work stations, laptops, file servers, web servers)Network printersVoIP phonesSecurity camerasMobile handheld devices (such as wireless barcode scanners, PDAs)13北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.5 Intermediary Devices and their Role on the NetworkConnect the individual hosts to the network and can connect multiple individual networks to form an internetwork. Examples :Network Access Devices (Hubs, switches, and wireless access points)Internetworking Devices (routers)Communication Servers and ModemsSecurity Devices (firewalls)14北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.5 Intermediary Devices and their Role on the NetworkFunctions:Regenerate and retransmit data signalsMaintain information about what pathways exist through the network and internetworkNotify other devices of errors and communication failuresDirect data along alternate pathways when there is a link failureClassify and direct messages according to QoS prioritiesPermit or deny the flow of data, based on security settings Intermediary devices direct the path of the data but do not generate or change the data content.重新生成和重新传输数据信号重新生成和重新传输数据信号维护有关网络和网际网络中存在哪些维护有关网络和网际网络中存在哪些通道的信息。通道的信息。将错误和通信故障通知其它设备将错误和通信故障通知其它设备发生链路故障时按照备用路径转发数发生链路故障时按照备用路径转发数据据根据根据 QoS QoS 优先级别分类和转发消息优先级别分类和转发消息根据安全设置允许或拒绝数据的通行根据安全设置允许或拒绝数据的通行 15北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.6 Network MediaModern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are:Wireless transmission 16北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.1.6 Network MediaCopper and Fiber OpticsMetallic wires within cablesGlass or plastic fibers (fiber optic cable)北京邮电大学思科网络技术学院17http:/cisco.bupt.edu.cn2.2 LANs, WANs, and Internetworks局域网、广域网和网际网络局域网、广域网和网际网络18北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.2.1 Local Area NetworksA network serving a home, building or campus is considered a Local Area Network (LAN)Networks infrastructures can vary greatly in terms of:The size of the area coveredThe number of users connectedThe number and types of services available19北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.2.2 Wide Area NetworksLANs separated by geographic distance are connected by a network known as a Wide Area Network (WAN)20北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.2.3 The Internet - A Network of NetworksThe internet is defined as a global mesh of interconnected networks. LANs and WANs may be connected into internetworks.21北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.2.4 Network RepresentationsImportant terms to remember are:Network Interface CardPhysical PortInterface 北京邮电大学思科网络技术学院22http:/cisco.bupt.edu.cn2.3 Protocols 协议协议23北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.1 Rules that Govern CommunicationsAll communication, is governed by predetermined rules called protocolsA protocol stack shows how the individual protocols within the suite are implemented on the host.The protocols are viewed as a layered hierarchyEach higher level service depending on the functionality defined by the protocols shown in the lower levelsExample：Using layers to describe face-to-face communication24北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.2 Network ProtocolsNetwork protocol suite must describe precise requirements and interactions. Protocols provide the format or structure of the messageThe format or structure of the message消息的格式或结构25北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.2 Network ProtocolsThe method by which networking devices share information about pathways with other networks提供网络设备之间共享其他网络路径信息的方法26北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.2 Network ProtocolsHow and when error and system messages are passed between devices在设备之间怎样、何时传递错误和系统信息。 27北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.2 Network ProtocolsThe setup and termination of data transfer sessions如何建立和终止数据传输28北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.3 Protocol Suites and Industry Standards组成协议簇的许多协议通常都要参考其它广泛采用的协议或行业标准。组成协议簇的许多协议通常都要参考其它广泛采用的协议或行业标准。标准是指已经受到网络行业认可并经过电气电子工程师协会标准是指已经受到网络行业认可并经过电气电子工程师协会 (IEEE) (IEEE) 或或 Internet Internet 工程工作小组工程工作小组 (IETF) (IETF) 之类标准化组织批准的流程或协议。之类标准化组织批准的流程或协议。29北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.4 The Interaction of Protocols The different protocols work together to ensure that the messages are received and understood by both parties.Example：Hypertext Transfer Protocol (HTTP) Transmission Control Protocol (TCP) Internet Protocol (IP).Network Access Protocols:30北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.3.5 Technology Independent ProtocolsNetworking protocols describe the functions that occur during network communications.Many diverse types of devices can communicate using the same sets of protocols. This is because protocols specify network functionality, not the underlying technology to support this functionality.北京邮电大学思科网络技术学院31http:/cisco.bupt.edu.cn2.4 Using Layered Models使用分层模型使用分层模型32北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.1 The Benefits of Using a Layered ModelUsing a layered model:Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below. （有助于协议设计有助于协议设计）Fosters competition because products from different vendors can work together. （促进竞争促进竞争）Prevents technology or capability changes in one layer from affecting other layers above and below. （避免技术或功能变化避免技术或功能变化时的相互时的相互影响影响）Provides a common language to describe networking functions and capabilities.（描述了通用的功能描述了通用的功能）33北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.2 Protocol and Reference ModelsTwo basic types of networking models: protocol models reference models34北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.7 The OSI Model35北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.3 The TCP/IP Model36北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.8 Comparing the OSI Model with the TCP/IP ModelCompare OSI and TCP/IP model37北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.5 Protocol Data Units and EncapsulationEncapsulation协议数据单元协议数据单元 （PDU）38北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.5 Protocol Data Units and Encapsulation39北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.4 The Communication ProcessA complete communication process includes these steps:1. Creation of data at the application layer of the originating source end device2. Segmentation and encapsulation of data as it passes down the protocol stack in the source end device 3. Generation of the data onto the media at the network access layer of the stack4. Transportation of the data through the internetwork, which consists of media and any intermediary devices5. Reception of the data at the network access layer of the destination end device 6. Decapsulation and reassembly of the data as it passes up the stack in the destination device 7. Passing this data to the destination application at the Application layer of the destination end device40北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.4 The Communication Process完整的通信过程包括如下步骤:1.在发送方源终端设备的应用层创建数据2. 当数据在源终端设备中沿协议栈向下传递时对其分段和封装3. 在协议栈网络接入层的介质上生成数据4. 通过由介质和任意中间设备组成的网际网络传输数据5. 在目的终端设备的网络接入层接收数据6. 当数据在目的设备中沿协议栈向上传递时对其解封和重组7. 将此数据传送到目的终端设备应用层的目的应用程序41北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.4.6 The Sending and Receiving ProcessThe process of sending and receiving messages.北京邮电大学思科网络技术学院42http:/cisco.bupt.edu.cn2.5 Network Addressing网络编址网络编址43北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.5.1 Addressing in the NetworkIt is critical for each piece of data to contain enough identifying information to get it to the correct destination. There are various types of addresses that must be included to successfully deliver the data from a source application running on one host to the correct destination application running on another.44北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.5.2 Getting the Data to the End DeviceThe first identifier is the host physical address；The Layer 2 address is unique on the local network and represents the address of the end device on the physical mediaMAC45北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.5.3 Getting the Data through the InternetworkLayer 3 address：46北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.5.4 Getting the Data to the Right ApplicationAt Layer 4, information contained in the PDU header identify the specific process or service running on the destination host device that will act on the data being delivered.Port number 47北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn2.6 LAB48北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cnSummary49北京邮电大学思科网络技术学院.http:/cisco.bupt.edu.cn