Model:TCP/IP协议组

概述: OSI参考模型 TCP/IP协议组 网络监视器

OSI参考模型 应用层 表达层 会话层 传输层 网络层 数据链路层 物理层

网络分层和优点 层 ：描述了所有需求的有效通讯过程，并把这些过程逻辑上的 组叫做层 分层的优点： 各层间相互独立，把网络操作分成低复杂性单元 灵活性好。某一层变化不会影响到其他层，设计者可专心设计和开发模块功能。 促进标准化工作

为什么分层? 语言 语言

OSI参考模型 应用层 表达层 会话层 传输层 网络层 数据链路层 物理层 应用层 表达层 会话层 传输层 网络层 数据链路层 物理层

OSI 模式 应用层 应用层 (高) 表示层 会话层 传输层 网络层 数据流层 数据链路层 物理层 Layer 2 of 2: Purpose: This figure orients the students to the next set of concepts. Emphasize: The Data Link layer of the OSI reference model is implemented by Switches and Bridges. These devices encapsulate date in “frames”. The Network layer of the OSI reference model is implemented by Routers. These devices encapsulate data in ‘packets’. The Transport layer of the OSI reference model is implemented by various protocols; one of which is TCP. TCP uses ports and encapsulates the data in ‘segments’. 网络层 数据流层 数据链路层 物理层

应用层作用 例子 Telnet SMTP HTTP FTP 应用层 用户接口 Slide 1 of 4: Purpose: This figure orients the students to the application layer. Emphasize: This layer discusses network applications rather than computer applications. So, applications such as spreadsheets, word processors, or presentation graphics are not the applications being described here. Network applications may be applications that support, electronic mail, file transfer, remote access, network management, and so on. Transition: The following discusses the presentation layer.

应用层 为用户提供一种通过应用程序访问网上信息的方法, 完成用户希望计算机完成的工作 常用协议:HTTP,FTP ,SMTP,DNS…

应用层作用 例子 Telnet SMTP HTTP FTP ASCII EBCDIC JPEG 应用层 用户接口 数据表示 加密等特殊处理过程 表示层 Slide 2 of 4: Purpose: This figure orients the students to the presentation layer. Emphasize: This layer discusses code formatting, data presentation standards, and conversion. Transition: The following discusses the session layer.

应用层作用 例子 Telnet HTTP ASCII EBCDIC JPEG Operating System/ 用户接口 ASCII EBCDIC JPEG 数据表示 加密等特殊处理过程 表示层 Operating System/ Application Access Scheduling 保证不同应用间的数据区分 会话层 Slide 3 of 4: Purpose: This figure orients the students to the session layer. Emphasize: This layer coordinates applications as they interact on different hosts. Examples of session-layer protocols include: NFS, SQL, RPC, and so on. Transition: The following displays the lower layers.

表达层和会话层 表达层以一种有序的有意义的方式表示信息,此层的 主要功能是数据翻译,数据加密,数据压缩等. 会话层在不同计算机的两个应用程序之间建立,维持 和结束确定的连接等.

应用层作用 例子 Telnet HTTP ASCII EBCDIC JPEG Operating System/ Application Access Scheduling 应用层 用户接口 数据表示 加密等特殊处理过程 表示层 保证不同应用间的数据区分 会话层 Slide 4 of 4: Purpose: This figure orients the students to the entire OSI model stack. Emphasize: The lower layers sit below the upper three layers. The remainder of this course is focused on the lower layers. Transition: The following discusses the physical layer of the OSI reference model. 传输层 网络层 数据链路层 物理层

数据流层的作用 例子 EIA/TIA-232 V.35 设备间接收或发送比特流 说明电压、线速和线缆等 物理层 Slide 1 of 5 Purpose: This figure orients the students to the physical layer of the OSI Model. Emphasize: The physical layer specifies the electrical, mechanical procedural, and functional requirements for activating, maintaining, and deactivating the physical link between systems. Certain physical standards are associated with certain data link standards. For example, 802.3 is used with data link standard 802.2 for Ethernet. It is not used in WAN connections. This is covered more in-depth later in the course. Transition: The following discusses Layer 2, the Data Link layer, of the OSI reference model. 设备间接收或发送比特流 说明电压、线速和线缆等 EIA/TIA-232 V.35 物理层

物理层功能 物理层负责的是数据在网线上的传输. 处理网络信道上位(bit)级的电/光通信, 该层主要关心传输使用的物理访问方式 它还定义用于传输数据的硬件特性,其基本功能是保证网络一方可正确接受另一方发送的信号 Ethernet 802.3 EIA/TIA-232 V.35 物理层 Purpose: This section describes the physical layer in more detail. Note: 802.3 is responsible for LANs based on the carrier sense multiple access collision detect (CSMA/CD) access methodology. Ethernet is an example of a CSMA/CD network. EIA/TIA-232 and V.35 are physical standards that support synchronous serial.

10Base2—细缆以太网 10Base5—粗缆以太网 物理层: Ethernet/802.3 10Base2—细缆以太网 10Base5—粗缆以太网 主机 Emphasize: Network topology is not necessarily connected to network technology. For example, many Ethernet networks have a backbone bus topology. However, adding a switch or a hub to an Ethernet network changes it to a star topology. IEEE 802.3u defines the standard for a CSMA/CD LAN operating at 100Mbps, Fast Ethernet. In the case of Ethernet, such as 10BaseT, the first part describes the speed of the cable, the second part describes whether it is baseband or broadband cable, the final part describes the media. So, 10BaseT is 10 Mbps baseband twisted-pair cable. 集线器 10BaseT—双绞线 多个主机

数据流层的作用 例子 802.3 / 802.2 HDLC EIA/TIA-232 V.35 将比特组合成字节进而组合成帧 Slide 2 of 5: Purpose: This figure orients the students to the data link layer. Emphasize: The data link layer provides data transport across a physical link. 802.3 is and physical and data link Ethernet protocol. It is used with the 802.2 standard. Transition: The following discusses Layer 3, the network layer, of the OSI reference model. 将比特组合成字节进而组合成帧 用MAC地址访问介质 错误发现但不能纠正 802.3 / 802.2 HDLC 数据链路层 设备间接收或发送比特流 说明电压、线速和线缆等 EIA/TIA-232 V.35 物理层

数据链路层功能 定义 源和目标的物理地址 与帧关联的高层协议 帧顺序 数据流控制 负责数据在子网内的传输, 其重要任务是创建和管理 由网络发送出去的桢 802.2 数据链路层 Frame Relay HDLC Ethernet Purpose: This figure compares physical standards to data link standards. Emphasize: As illustrated, certain physical standards are associated with certain data link standards. For example, 802.3 is used with data link standard 802.2 for Ethernet. It is not used in WAN connections. 802.3 EIA/TIA-232 v.35 物理层

数据链路层功能(续) MAC子层- 802.3 MAC 地址 # 字节 8 6 6 2 可变长 4 前导符 目标地址 源地址 长度 数据 FCS Ethernet II 在这里用 “Type”指明上层协议，所以不用 802.2. Emphasize: All MAC addresses on a LAN must be unique. Two devices with the same MAC address cannot be on the same data link. Note: The IEEE assigned vendor code is just one of Cisco’s many MAC vendor codes. Cisco has many more, many of which came with Cisco’s acquisitions. 0000.0C xx.xxxx IEEE 分配 厂商自己分配 MAC 地址

数据流层的作用 例子 IP IPX 802.3 / 802.2 HDLC EIA/TIA-232 V.35 提供路由器用来决定路径的逻辑寻址 网络层 Slide 3 of 5: Purpose: This figure orients the students to the network layer. Emphasize: Network layer is where IP occurs. Transition: The following discusses Layer 4, the transport layer, of the OSI reference model. 将比特组合成字节进而组合成帧 用MAC地址访问介质 错误发现但不能纠正 802.3 / 802.2 HDLC 数据链路层 设备间接收或发送比特流 说明电压、线速和线缆等 EIA/TIA-232 V.35 物理层

网络层功能(续) 逻辑地址提供分层结构的网络 需要的配置 利用配置信息来识别到达目标网络的路径 1.0 4.0 1.1 4.1 2.1 2.2 1.3 4.3 1.2 4.2 E0 S0 S0 E0 路由表 路由表 Emphasize: Routers maintain routes in routing tables. Before any routing can be done an administrator must configure a router with certain key information such as addresses and tell the router how to determine the best route to use. This is different than a switch which is a plug and play device. 目标网络 端口 距离 目标网络 端口 距离 1 E0 1 S0 1 2 S0 2 S0 4 S0 1 4 E0 逻辑地址提供分层结构的网络 需要的配置 利用配置信息来识别到达目标网络的路径

数据流层的作用 例子 TCP UDP SPX IP IPX 802.3 / 802.2 HDLC EIA/TIA-232 V.35 可靠或不可靠的数据传输 数据重传前的错误纠正 TCP UDP SPX 传输层 提供路由器用来决定路径的逻辑寻址 IP IPX 网络层 Slide 4 of 5: Purpose: This figure orients the students to the transport layer. Emphasize: The Transport layer of the OSI reference model is implemented by various protocols; one of which is TCP. TCP uses ports and encapsulates the data in ‘segments’. TCP is connection oriented so it offers reliable service. The other major transport layer protocol discussed in this course is UDP. It offers speed but no reliability because it is connectionless. Transition: The following presents the entire OSI stack again. 将比特组合成字节进而组合成帧 用MAC地址访问介质 错误发现但不能纠正 802.3 / 802.2 HDLC 数据链路层 设备间接收或发送比特流 说明电压、线速和线缆等 EIA/TIA-232 V.35 物理层

传输层功能 整个协议层次结构中 最核心一层,它包含有 关传输数据的所有细 节 它为源端机和目的机 之间提供性能可靠,价 格合理的数据传输 Transport TCP UDP SPX Purpose: This figure describes the transport layer. Emphasize: Two transport layer protocols in the IP stack are TCP and UDP. TCP will offer more reliability because it is connection oriented. UDP guarantees no reliability. Sequence Packet Exchange (SPX) is the transport layer protocol used by IPX. It is also connection oriented. Newer versions of IPX support TCP and UDP as well. Network IP IPX

数据流层的作用 例子 TCP UDP SPX IP IPX 802.3 / 802.2 HDLC EIA/TIA-232 V.35 应用层 表示层 例子 会话层 可靠或不可靠的数据传输 数据重传前的错误纠正 TCP UDP SPX 传输层 提供路由器用来决定路径的逻辑寻址 IP IPX 网络层 Slide 5 of 5: Purpose: This figure reviews the entire OSI model stack. Emphasize: The upper layers sit above the lower layers. Transition: The following discusses encapsulation and de-encalsulation. 将比特组合成字节进而组合成帧 用MAC地址访问介质 错误发现但不能纠正 802.3 / 802.2 HDLC 数据链路层 设备间接收或发送比特流 说明电压、线速和线缆等 EIA/TIA-232 V.35 物理层

封装 封装 （ encapsulate/encapsulation）：数据要通过网络进行传输，要从高层一层一层的向下传送，如果一个主机要传送数据到别的主机，先把数据包装到一个特殊协议报头中，这个过程叫 封装

封装数据 PDU Segment 传输层 网络层 Packet 数据链路层 Frame 物理层 Bits 应用层 表示层 会话层 Upper Layer Data Segment 传输层 TCP Header Upper Layer Data 网络层 Packet IP Header Data Purpose: This figure illustrates encapsulation. Emphasize: The protocol data units (PDUs) are the terms used in the industry and in this course to describe data at the different layers. Encapuslation is a key concept that illustrates how data is formatted prior to being sent across a link. This example is an illustration is Ethernet (or token ring) at the data link and physical layer and TCP/IP at the network and transport layers. Transition: The following discusses de-encalsulation. LLC Header Data FCS 数据链路层 Frame MAC Header Data FCS 物理层 Bits 0101110101001000010

解封装数据 传输层 网络层 数据链路层 物理层 应用层 表示层 会话层 上层数据 上层数据 TCP 头 TCP+上层数据 IP 头 Purpose: This figure illustrates de-encapsulation. Emphasize: At the destination, the headers at each layer are stripped off as the data moves back up the stack. TCP+上层数据 IP 头 IP + TCP +上层数据 数据链路层 LLC 头 LLC 头 + IP + TCP + 上层数据 MAC 头 物理层 0101110101001000010

协议 协议是什么？ 一组规则或标准 用来连接网络中的计算机

协议种类 开放协议 公共的工业标准 Internet TCP/IP 特定厂商的协议 不同厂商开发用于特定 的环境 IPX/SPX

一般协议 Transmission Control Protocol/Internet Protocol (TCP/IP) Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) NetBIOS Enhanced User Interface (NetBEUI) AppleTalk

拨号协议 TCP/IP PPP NetBEUI TCP/IP or IPX/SPX PPP TCP/IP SLIP Internet Remote Access Client Windows 2000 Professional Remote Access Server Windows 2000 Server NetBEUI TCP/IP or IPX/SPX PPP TCP/IP SLIP Local Area Network Remote Access Server Windows 2000 Server UNIX SLIP Server

TCP/IP, IPX/SPX, NetBEUI traffic 虚拟专用网协议 Internetwork must be IP-based Header compression No tunnel authentication Uses MPPE encryption PPTP Internetwork can be IP, frame relay, X.25, or ATM-based Header compression Tunnel authentication Uses IPSec encryption L2TP Remote Access Client Remote Access Server TCP/IP, IPX/SPX, NetBEUI traffic PPTP or L2TP Ensures data security in IP-based communications Can be used by both PPTP and L2TP IPSec