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Internet Protocol Stack Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 What’s the Internet: “nuts and bolts” view PC millions of connected computing devices: hosts = end systems wireless laptop running network cellular handheld apps communication links fiber, copper, access points radio, satellite wired links transmission rate = bandwidth routers: forward router packets (chunks of data) Mobile network server Global ISP Home network Regional ISP Institutional network What’s the Internet: “nuts and bolts” view protocols control sending, Mobile network receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Global ISP Home network Regional ISP Institutional network What’s the Internet: a service view communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery The topology structure Network Node + communication lines, reflecting the network structure of the inter-entity relations Bus Star Mesh Tree Ring What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time Q: Other human protocols? 关于网络协议的中文说明 计算机网络中的数据交换必须遵守事先约定好 的规则。 这些规则明确规定了所交换的数据的格式以及 有关的同步问题(同步含有时序的意思)。 网络协议(network protocol),简称为协议, 是为进行网络中的数据交换而建立的规则、标 准或约定。 网络协议的组成要素 语法 数据与控制信息的结构或格式 。 语义 需要发出何种控制信息,完成何种动 作以及做出何种响应。 同步 事件实现顺序的详细说明。 Physical Media Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet Physical Media: coax, fiber Coaxial cable: Fiber optic cable: conductors bidirectional baseband: pulses, each pulse a bit high-speed operation: two concentric copper single channel on cable legacy Ethernet broadband: multiple channels on cable HFC glass fiber carrying light high-speed point-to-point transmission (e.g., 10’s100’s Gps) low error rate: repeaters spaced far apart ; immune to electromagnetic noise Physical media: radio signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Radio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude The Network Core mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” (message-switching) Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time division Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Numerical example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit Let’s work it out! Network Core: Packet Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time Node receives complete packet before forwarding Packet switching versus circuit switching Packet switching allows more users to use network! 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than .0004 N users 1 Mbps link Q: how did we get value 0.0004? Packet switching versus circuit switching Is packet switching a “slam dunk winner?” great for bursty data resource sharing simpler, no call setup excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Protocol “Layers” Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Why layering? Dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? 计算机网络的体系结构 计算机网络的体系结构(architecture)是计算 机网络的各层及其协议的集合。 体系结构就是这个计算机网络及其部件所应完 成的功能的精确定义。 实现(implementation)是遵循这种体系结构的 前提下用何种硬件或软件完成这些功能的问题 。 体系结构是抽象的,而实现则是具体的,是真 正在运行的计算机硬件和软件。 Internet protocol stack application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Network Software Protocol Hierarchies Layers, protocols, and interfaces Notions Entity: any hardware of software process that can send or receive message; the active elements of every layer. Peer entities: two entities that locate at the same layer of different system. Protocol is used between peer entities. Interface: the interface between the contiguous layers. Service: the function of one layer and its underlying layers, services are provided to the contiguous above layer through interface. Protocol Stack: the set of protocols of a system. Network Architecture: the layer structure and the protocols. Services to Protocols Relationship The relationship between a service and a protocol. ISO/OSI reference model presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical ISO/OSI reference model A Critique of the OSI Model and Protocols Why OSI did not take over the world • Bad timing • Bad technology • Bad implementations • Bad politics Bad Timing The apocalypse of the two elephants. TCP/IP RM Example of TCP/IP 4-layer protocol A B 4 Application router 3 Transport 2 1 Application Transport Internet Interface network1 Internet Internet Interface Interface network2 A Critique of the TCP/IP Reference Model Problems: • Service, interface, and protocol not • • • • distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to replace Hybrid Model TCP/IP Model: Five-layer structure Internet protocol stack The hybrid reference model to be used in this book. Node 1 sends data to Node 2 Computer 1 AP1 5 pass data to the application layer add the application head, becomes msg Computer 2 AP2 5 4 4 3 3 2 2 1 1 Computer 1 Computer 2 AP2 AP1 5 pass the msg to transport layer 5 4 add the transport head 4 3 3 2 2 1 1 Computer 1 Computer 2 AP2 AP1 5 5 4 pass the segment to network 4 3 add the network head, becomes datagram 3 2 2 1 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 pass the datagram to the data link layer 3 2 add the link head and tail, becomes frame 2 1 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 3 2 pass the frame to the physical layer 2 1 physical layers passes the bit stream to the media 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 3 2 2 1 electronic signal is transmitted in physical media from the sender PHY to the receiver PHY physical media 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 3 2 2 1 the physical layer receives the bit stream, and hands over frame to the above data link layer 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 3 2 1 data link layer picks out the datagram and hands over to the network layer 2 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 network layer picks out the segment and hands over to the transport layer 3 2 2 1 1 Computer 1 Computer 2 AP2 AP1 5 4 5 transport layer picks out the msg and hands over to the application layer 4 3 3 2 2 1 1 Computer 1 AP1 5 Computer 2 application layer picks out the data and hands over to the application AP2 5 4 4 3 3 2 2 1 1 Computer 1 AP1 I received the data sent by AP1! Computer 2 AP2 5 5 4 4 3 3 2 2 1 1 Computer 1 Computer 2 app head AP1 5 4 3 trans head H5 application data 5 H4 H5 application data 4 H3 H4 H5 application data H3 H4 H5 application data net head link head AP2 application data link tail 3 2 H2 T2 2 1 10100110100101 bit stream 110101110101 1 Computer 1 Computer 2 AP2 AP1 5 5 4 4 3 After receiving the bit stream, the physical layer of computer 2 hands it over to the link layer 3 2 H2 T2 2 1 10100110100101 bit stream 110101110101 1 H3 H4 H5 application data Computer 1 Computer 2 AP2 AP1 5 4 After removing the head and tail of the frame, link Layer hands over the data to the network layer. 3 2 1 H2 H3 H4 H5 application data H3 H4 H5 application data 5 4 3 T2 2 1 Computer 1 AP1 5 Computer 2 After removing the head, the network layer hands over the data to the transport layer. AP2 5 4 H4 H5 application data 4 3 H3 H4 H5 application data 3 2 2 1 1 Computer 1 After removing the head, the transport layer AP1 hands over the data to the application layer. 5 4 H4 Computer 2 AP2 H5 application data 5 H5 application data 4 3 3 2 2 1 1 Computer 1 Computer 2 application data AP1 5 4 3 H5 application data After removing the head, the application layer hands over the data to the application. AP2 5 4 3 2 2 1 1 Computer 1 AP1 I received the data sent by AP1! Computer 2 AP2 5 5 4 4 3 3 2 2 1 1 Encapsulation source message segment M Ht M datagram Hn Ht M frame Hl Hn Ht M application transport network link physical link physical switch destination M Ht M Hn Ht Hl Hn Ht M M application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht M router Functions of each layer bit prescribe the electronic parameter of the physical layer. prescribe the connector To transfer bit stream physical layer establish, maintain and release physical connection between two entities of data link layer. Functions of each layer data link establish, maintain and release data link, show a right link to the network frame layer dividing and synchronizatio error n of frames detection and control access control To transfer data from one node to its adjacent node Functions of each layer routing Host-to-host data transmission network datagram forwarding Functions of each layer segment sequence control transport provide logical communication between app processes error control flow control Process-to-Process (end2end) data transmission Functions of each layer provide interface for users application message Protocols and networks Protocols and networks in the TCP/IP model initially. Internet Trends Internet Trends 2020: Internet use reaches 5 billion worldwide Internet Trends in China 2014年1月16日,中国互联网络信息中心( CNNIC)在京发布第33次《中国互联网络 发展状况统计报告》 Internet Trends in China Internet Trends in China Internet Trends in China Internet Trends in China Internet Trends in China Internet Trends in China Internet Trends in China Introduction 1-73 Internet Trends in China Introduction 1-74 Internet Trends in China Introduction 1-75 Internet Trends in China Introduction: Summary Covered a “ton” of material! Internet overview what’s a protocol? network edge, core, access network packet-switching versus circuit-switching performance: loss, delay, throughput layering, service models Internet trends