* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 4th Edition: Chapter 1
Survey
Document related concepts
Multiprotocol Label Switching wikipedia , lookup
Net neutrality wikipedia , lookup
Asynchronous Transfer Mode wikipedia , lookup
Wireless security wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Net neutrality law wikipedia , lookup
Distributed firewall wikipedia , lookup
Computer network wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Internet protocol suite wikipedia , lookup
Network tap wikipedia , lookup
Airborne Networking wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Deep packet inspection wikipedia , lookup
Packet switching wikipedia , lookup
Transcript
Table of Contents Chapter 1 Introduction Chapter 2 Application Layer Chapter 3 Transport Layer Chapter 4 Network Layer Chapter 5 Link Layer and LAN Chapter 6 Wireless and Mobile Network Chapter 7 Multimedia Network Chapter 8 Network Security Chapter 9 Network Management Introduction 1-1 Computer Networks 网络应用 (Email,Web,P2P,多媒体等) 网 络 管 理 网络互联 (TCP/IP、IP路由等) 物理网络 网 络 安 全 Chapter 1 Introduction what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models Introduction 1-3 Chapter 2 Application Layer network application models client-server paradigm peer-to-peer paradigm learn about protocols by examining popular application-level protocols HTTP FTP SMTP / POP3 / IMAP DNS programming network applications socket API Introduction 1-4 Chapter 3 Transport Layer understand principles behind transport layer services: multiplexing/demultiplexing reliable data transfer flow control congestion control learn about transport layer protocols in the Internet: UDP: connectionless transport TCP: connection-oriented transport TCP congestion control Introduction 1-5 Chapter 4 Network Layer network layer service models Virtual circuit and datagram networks forwarding versus routing how a router works What’s inside a router routing (path selection) Routing algorithms Routing in the Internet dealing with scale advanced topics: IPv6, mobility Introduction 1-6 Chapter 5 Link Layer and LAN understand principles behind data link layer services: error detection, correction sharing a broadcast channel: multiple access link layer addressing reliable data transfer, flow control: done! instantiation and implementation of various link layer technologies Introduction 1-7 Chapter 6: Wireless and Mobile Networks # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! computer nets: laptops, palmtops, PDAs, Internetenabled phone promise anytime untethered Internet access two important (but different) challenges wireless: communication over wireless link mobility: handling the mobile user who changes point of attachment to network Introduction 1-8 Chapter 7 Multimedia Network Principles classify multimedia applications identify network services applications need making the best of best effort service Protocols and Architectures specific protocols for best-effort mechanisms for providing QoS architectures for QoS Introduction 1-9 Chapter 8 Network Security understand principles of network security: cryptography and its many uses beyond “confidentiality” authentication message integrity security in practice: firewalls and intrusion detection systems security in application, transport, network, link layers Introduction 1-10 Chapter 9 Network Management introduction to network management motivation major components Internet network management framework MIB: management information base SMI: data definition language SNMP: protocol for network management security and administration presentation services: ASN.1 Introduction 1-11 Chapter 1 Introduction Computer Networking: A Top Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. Introduction 1-12 Chapter 1: Introduction Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history Introduction 1-13 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-14 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 Introduction 1-15 “Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones Introduction 1-16 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 Global ISP Home network Regional ISP Institutional network Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Introduction 1-17 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 Introduction 1-18 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 Introduction 1-19 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? Introduction 1-20 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-21 A closer look at network structure: network edge: applications and hosts access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks Introduction 1-22 The network edge: end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server model client host requests, receives service from always-on server client/server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent Introduction 1-23 Access networks and physical media Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Introduction 1-24 Dial-up Modem central office home PC home dial-up modem telephone network Internet ISP modem (e.g., AOL) Uses existing telephony infrastructure Home is connected to central office up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: not “always on” Digital Subscriber Line (DSL) Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data home phone Internet DSLAM telephone network splitter DSL modem home PC central office Also uses existing telephone infrastruture up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office Residential access: cable modems Does not use telephone infrastructure Instead uses cable TV infrastructure HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router unlike DSL, which has dedicated access Introduction 1-27 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-28 Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend cable distribution network (simplified) home Introduction 1-29 Cable Network Architecture: Overview server(s) cable headend cable distribution network home Introduction 1-30 Cable Network Architecture: Overview cable headend cable distribution network (simplified) home Introduction 1-31 Cable Network Architecture: Overview FDM (more shortly): V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels cable headend cable distribution network home Introduction 1-32 Fiber to the Home ONT optical fibers Internet OLT central office ONT optical fiber optical splitter ONT Optical links from central office to the home Two competing optical technologies: Passive Optical network (PON) Active Optical Network (PAN) Much higher Internet rates; fiber also carries television and phone services Ethernet Internet access 100 Mbps Institutional router Ethernet switch To Institution’s ISP 100 Mbps 1 Gbps 100 Mbps server Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into Ethernet switch Wireless access networks shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access provided by telco operator ~1Mbps over cellular system (EVDO, HSDPA) next up (?): WiMAX (10’s Mbps) over wide area router base station mobile hosts Introduction 1-35 Home networks Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point to/from cable headend cable modem router/ firewall Ethernet wireless laptops wireless access point Introduction 1-36 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 Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet unguided media: signals propagate freely, e.g., radio Introduction 1-37 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 Introduction 1-38 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 Introduction 1-39 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-40 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” Introduction 1-41 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 Introduction 1-42 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls dividing link bandwidth into “pieces” frequency division time division resource piece idle if not used by owning call (no sharing) Introduction 1-43 Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Introduction 1-44 T1标准 E1标准 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! Introduction 1-47 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 Introduction 1-48 Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet A B statistical multiplexing C 1.5 Mb/s queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. Introduction 1-49 Packet-switching: store-and-forward L R takes L/R seconds to R transmit (push out) packet of L bits on to link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link delay = 3L/R (assuming zero propagation delay) R Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay = 15 sec more on delay shortly … Introduction 1-50 Circuit、Message and Packet Switching 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? Introduction 1-52 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)? Introduction 1-53 Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP Tier 1 ISP Introduction 1-54 Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … . … … … to/from customers Introduction 1-55 Internet structure: network of networks “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier 1 ISP Tier-2 ISPs also peer privately with each other. Tier-2 ISP Tier-2 ISP Introduction 1-56 Internet structure: network of networks “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) local ISP Local and tier3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP Introduction 1-57 Internet structure: network of networks a packet passes through many networks! local ISP Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP Introduction 1-58 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-59 How do loss and delay occur? packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-60 Four sources of packet delay 1. nodal processing: check bit errors determine output link 2. queueing time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing Introduction 1-61 Delay in packet-switched networks 3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R transmission A 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s Note: s and R are very different quantities! propagation B nodal processing queueing Introduction 1-62 Caravan analogy 100 km ten-car caravan toll booth cars “propagate” at 100 km/hr toll booth takes 12 sec to service car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? 100 km toll booth Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62(2+60) minutes Introduction 1-63 Caravan analogy (more) 100 km ten-car caravan 100 km toll booth Cars now “propagate” at 1000 km/hr Toll booth now takes 1 min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? toll booth Yes! After 7(1+6) min, 1st car at 2nd booth and 3 cars still at 1st booth. 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! See Ethernet applet at AWL Web site Introduction 1-64 Nodal delay d nodal d proc d queue d trans d prop dproc = processing delay typically a few microsecs or less dqueue = queuing delay depends on congestion dtrans = transmission delay = L/R, significant for low-speed links dprop = propagation delay a few microsecs to hundreds of msecs Introduction 1-65 Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! http://wps.pearsoned.com/ecs_kurose_compnetw_6/216/55463/141987 Introduction 1-66 00.cw/index.html “Real” Internet delays and routes What do “real” Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes Introduction 1-67 “Real” Internet delays and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * * means no response (probe lost, router not replying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms Introduction 1-68 Packet loss queue (aka buffer) preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) A B packet being transmitted packet arriving to full buffer is lost Introduction 1-69 Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over long(er) period of time link capacity that can carry server, with server sends bits pipe Rs bits/sec fluid at rate file of F bits (fluid) into pipe Rs bits/sec) to send to client link that capacity pipe can carry Rfluid c bits/sec at rate Rc bits/sec) Introduction 1-70 Throughput (more) Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link link on end-end path that constrains end-end throughput Introduction 1-71 Throughput: Internet scenario per-connection end-end throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-72 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-73 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? Introduction 1-74 Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing A series of steps Introduction 1-75 Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing departure airport airplane routing airplane routing intermediate air-traffic control centers arrival airport Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Introduction 1-76 Layering of mail system 用 户 (写信人) 用户/邮局 约定 用户间约定 用 户 (收信人) 邮局间约定 邮 局 邮局/运输 部门约定 邮 局 运输部门间约定 运输部门 甲地 运输部门 乙地 用户子系统 邮局子系统 运输子系统 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? Introduction 1-78 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 application transport network link physical neighboring network elements PPP, Ethernet physical: bits “on the wire” Introduction 1-79 (5) Application Layer RPC 111 SNMP TFTP SMTP FTP TELNET 161 69 25 21 23 UDP TCP IP RPC 111 SNMP TFTP SMTP FTP 161 69 25 21 UDP TELNET 23 TCP IP Introduction 1-80 Application Layer Scope Process-Process Data Unit Block/file/… Application Layer Protocol Application Software SMTP Email Outlook/Mail-Server http WWW IE/IIS Server Introduction 1-81 Example: HTTP response message 1.status line (protocol status code status phrase) HTTP/1.1 200 OK Connection close Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) 2.header Last-Modified: Mon, 22 Jun 1998 …... lines Content-Length: 6821 Content-Type: text/html blank line 3.data, e.g., requested HTML file data data data data data ... Introduction 1-82 (4) Transport Layer Applications Server 1 UDP TCP 6 UDP TCP 6 17 IP Host D Applications Server 1 Transp 17 IP Internet Introduction 1-83 Transport Layer Scope End-to-end Data Unit Segment (段) Function Process Addressing Error Control Flow Control QoS Provision Examples TCP, UDP Introduction 1-84 (3)Network Layer Host A P2 P1 P2 Packet 1 Packet 2 P2 Data C P2 Packet N P1 P1 D P1 P2 Data P1 P1 P2 Host B Introduction 1-85 Network Layer Scope Network Wide ,Between any two Hosts Data Unit Packet (分组) Function Inter-networking (网络互连) Routing (路由) Congestion Control (拥塞控制) Examples IP, IPX Introduction 1-86 (2) Data Link Layer Scope Link ,Between Neighboring Points Data Unit Frame (帧) Function Error Control Flow Control 2 Sub-layers MAC (Media Access Control,介质访问控制) LLC (Logical Link Control,逻辑链路控制) Examples SDLC, PPP, HDLC Introduction 1-87 (1)Physical Layer Example EIA RS-232-C, RS-449,RS-422,RS-423,RS-530 CCITT V.24,V.28,V.35,X.21,X.3,X.28,X.29 IEEE 10Base5,10Base2,10BaseT Introduction 1-88 Physical Layer Mechanical Feature 1 2 3 4 5 6 7 8 9 10 14 15 16 17 18 19 20 21 22 11 23 12 24 13 25 RS-232-C 25 Pins Introduction 1-89 Physical Layer Electrical Feature MC1488 TTL 电平 “1”< -3V “0”> +3V MC1489 TTL 电平 Introduction 1-90 Physical Layer Signal Definition DTE 计算机 或 终端 ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ 保护地(Protective Ground) 发送(TxD) 接收(RxD) 请求发送(RTS) 允许发送(CTS) DCE就绪(DSR) 信号地(Signal Ground) DCE 调制 解调器 载波检测(DCD) 20 DTE就绪(DTR) 22 振铃指示(RI) Introduction 1-91 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 Introduction 1-92 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 Introduction 1-93 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-94 Network Security 今年5月16日,美出炉《 International Strategy for Cyberspace》,第一次将陆、海、空、太空、网络五大 空间并列,强调美国(网络空间)国家、全球化、机构与 个体意识。特别提到对would-be攻击者,必要时采取 先发制人策略,并明确表示有权动用任何手段,包括 外交、信息、军事和经济手段 今年7月19日,美国防部出台《DoS Strategy for Operating in Cyberspace》 Network Security 当今世界,网络信息安全形势极其严峻。各国十分重 视信息安全,如美国多年来一直将信息安全技术列为 国防基础技术,并作为制信息权的关键手段。 2009年6月25日,美军成立网络战司令部; 2010年7月19日,我军成立总参信息保障基地; 2011年6月30日,我军成立总参信息化部。 Network Security attacks on Internet infrastructure: infecting/attacking hosts: malware, spyware, worms, unauthorized access (data stealing, user accounts) denial of service: deny access to resources (servers, link bandwidth) Internet not originally designed with (much) security in mind original vision: “a group of mutually trusting users attached to a transparent network” Internet protocol designers playing “catch-up” Security considerations in all layers! Introduction 1-97 What can bad guys do: malware? Spyware: Worm: infection by downloading infection by passively web page with spyware receiving object that gets itself executed records keystrokes, web sites visited, upload info self- replicating: propagates to collection site to other hosts, users Virus infection by receiving object (e.g., e-mail attachment), actively executing self-replicating: propagate itself to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data) Introduction 1-98 网络安全问题日益突出 攻击类型 • • • • • 信息窃取 电子欺骗 拒绝服务 病毒 非法入侵 网络各层均存在攻击行为 • 终端, 局域网, 交换机, 服务器, 应用等 攻击的复杂性增加 • 工具包 • 协作式攻击 无线 & 移动性 • 无线协议安全性还是不好 • 移动设备物理上就是不安全的 上网计算机上受到的攻击数据统计 浏览器配置被修改 71.9% 网络系统无法使用 50.1% 数据或文件被损坏 45.0% 操作系统崩溃 41.5% 32.3% QQ、MSN密码,邮箱帐号被盗 网络游戏密码,虚拟资产被盗 18.5% 受到远程控制 10.8% 电脑使用变慢 7.9% 没有造成实质危害 3.1% 网上银行密码、帐号被盗 2.5% 网络系统运行慢 1.7% 其他 2% 0% 20% 40% 60% 80% 100% Denial of Service attacks attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the network (see malware) 3. send packets toward target from compromised hosts target Introduction 1-101 真实案例:美国、韩国网站被攻击疑案 2009年8月,韩国多个政府网站持续遭到不明黑客发动的分布 式拒绝服务攻击,造成部分网站瘫痪长达4个小时。 韩国国家情报院院长元世勋声称,追踪到这些攻击来自于全球 16个国家和地区的86个IP地址。尽管韩方猜测攻击极有可能来 自于朝鲜,但苦于找不到足够的证据,因而不能确定黑客真实 身份,也不能还原出完整的攻击过程。 僵尸网络 僵尸网络(Botnet):使一组联网计算机感染僵尸(Bot) 病 毒,进而被控制用于发起各种网络攻击行为,从而导致整 个基础网络瘫痪或信息系统崩溃,亦可导致机密信息泄漏 或网络欺诈等犯罪活动。 拒绝服务攻击 发送垃圾邮件 窃取秘密 滥用资源 。。。 伪造的商业网站示例 中国银行网站 正确: http://www.bank-of-china.com 假冒: http://www.bank-off-china.com 农业银行 工商银行 www.95599.cn www.icbc.com.cn 建设银行 www.ccb.cn “钓鱼”邮件示例 Sniff, modify, delete your packets Packet sniffing: broadcast media (shared Ethernet, wireless) promiscuous network interface reads/records all packets (e.g., including passwords!) passing by C A src:B dest:A payload B Ethereal software used for end-of-chapter labs is a (free) packet-sniffer more on modification, deletion later Introduction 1-106 Packet sniffing: Masquerade as you IP spoofing: send packet with false source address C A src:B dest:A payload B Introduction 1-108 Masquerade as you IP spoofing: send packet with false source address record-and-playback: sniff sensitive info (e.g., password), and use later password holder is that user from system point of view A C src:B dest:A user: B; password: foo B Introduction 1-109 Masquerade as you IP spoofing: send packet with false source address record-and-playback: sniff sensitive info (e.g., password), and use later password holder is that user from system point of view later ….. C A src:B dest:A user: B; password: foo B Introduction 1-110 Honey Pot Chicken Hiker Network Security more throughout this course Chapter 8: focus on security Crypographic techniques: obvious uses and not so obvious uses Introduction 1-112 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction 1-113 Internet History 1961-1972: Early packet-switching principles 1961: Kleinrock - queueing theory shows effectiveness of packetswitching 1964: Baran - packetswitching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes Introduction 1-114 Initial Expansion of the ARPANET Dec. 1969 July 1970 Apr. 1972 Mar. 1971 Sept. 1972 Introduction RFC 527: ARPAWOCKY; RFC 602: The Stockings Were Hung by the Chimney with Care 1-115 115 Internet History 1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite network in Hawaii 1974: Cerf and Kahn architecture for interconnecting networks 1976: Ethernet at Xerox PARC ate70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today’s Internet architecture Introduction 1-116 Internet History 1980-1990: new protocols, a proliferation of networks 1983: deployment of TCP/IP 1982: SMTP e-mail protocol defined 1983: DNS defined for name-to-IP-address translation 1985: Ftp protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks Introduction 1-117 Internet History 1990, 2000’s: commercialization, the Web, new apps Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web Late 1990’s – 2000’s: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps Growth of the Internet in Terms of Number of Hosts Number of Hosts on Web: Aug. 1981 213 Oct. 1984 1,024 Dec. 1987 28,174 Oct. 1990 313,000 Jul. 1993 1,776,000 Jul. 1996 19,540,000 Jul. 1999 56,218,000 Jul. 2004 285,139,000 Jul. 2005 353,284,000 Jul. 2006 439,286,000 Jul. 2007 489,774,000 CAIDA router level view Introduction 1-119 119 Internet History 2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) more applications: YouTube, gaming wireless, mobility Introduction: Summary Covered a “ton” of material! Internet overview what’s a protocol? network edge, core, access network packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service models security history You now have: context, overview, “feel” of networking more depth, detail to follow! Homework Review Questions: 18, 23 Problems: 4, 5, 6, 9, 15, 18, 24 Discussion: 4 Extensive Reading L. Kleinrock. History of the Internet and its Flexible Future. IEEE Wireless Communications, 15(1), Feb. 2008