01-1 Chapter1 Computer Networking.pptx

第1页：计算机网络：自顶向下方法

计算机网络：自顶向下方法

Computer Networking——A Top Down Approach Featuring the Internet

第2页：本章小结

本章小结

• Our goal of learning Computer Network
• Main contents Chapter 1: Introduction Chapter 2: Application Layer Chapter 3: Transport Layer Chapter 4: Network Layer Chapter 5: Link Layer and LANs Chapter 6: Wireless and Mobile Networks Chapter 8: Network Security Chapter 9: Network Management

第3页：本章小结

本章小结

• Teaching material Computer Networking——A Top Down Approach Featuring the Internet,4 rdedition. 2008 Jim Kurose, Keith Ross Addison-Wesley,.
• Reference material计算机网络谢希仁主编
• 54 h, 14 weeks
• Testing

第4页：第1章：概述本章目标

第1章：概述本章目标

• get “feel” andterminology
• more depth, detaillaterin course
• approach:
  • use Internet asexample Overview:
• what’s the Internet?
• what’s a protocol?
• network edge; hosts, accessnet, physical media
• network core: packet/circuit switching, Internet structure
• performance: loss, delay,throughput
• security
• protocol layers, service models
• history

第5页：第1章路线图

第1章路线图

• 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

第6页：什么是因特网构成

什么是因特网构成

• millions of connected computing devices:hosts = end systems
  • running networkapps Home network Institutional network Mobile network Global ISPRegional ISProuter PCserver wireless laptop cellular handheld wiredlinks access points
• communication links
  • fiber, copper,radio, satellite
  • transmissionrate =bandwidth
• routers:forward packets (chunks ofdata)

第7页：“Cool” internet appliances World’s small

“Cool” internet appliances World’s small

“Cool” internet appliances World’s smallest web server picture frame toaster +weather forecaster Internet phones

第8页：什么是因特网构成

什么是因特网构成

• protocols control sending,receiving of msgs
  • e.g., TCP, IP, HTTP, Skype, Ethernet
• Internet:“network ofnetworks”
  • loosely hierarchical
  • public Internet versus private intranet
• Internet standards
  • RFC: Request for comments
  • IETF: Internet Engineering Task Force Home network Institutional network Mobile network Global ISPRegional ISP

第9页：什么是因特网服务视角

什么是因特网服务视角

• communication infrastructure enables distributed applications:
  • Web, Vo IP, email, games,e-commerce, file sharing
• communication services provided to apps:
  • reliable data deliveryfrom source todestination
  • “best effort” (unreliable)data delivery

第10页：What’s protocol?human protocols

What’s protocol?human protocols

• “what’s the time?”
• “I have a question”
• introductions… specific msgs sent… specific actions takenwhen msgs received,or other events network protocols:
• machines rather thanhumans
• all communication activity in Internet governed by protocols protocols define format,order of msgs sent andreceived among networkentities, and action staken on msgtransmission, receipt

第11页：What’s protocol?a human protocol and

What’s protocol?a human protocol and

What’s a protocol?a human protocol and a computer network protocol:Q:Other human protocols?Hi Hi Got thetime?2:00TCP connectionre quest TCP connection response Get

第12页：第1章路线图

第1章路线图

• 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

第13页：进一步观察 网络结构

进一步观察 网络结构

• network edge:applications andhosts
• access networks,physical media:wired, wireless communication links
• network core:
  • interconnected routers
  • network ofnetworks

第14页：网络边缘

网络边缘

• end systems (hosts):
  • run application programs
  • e.g. Web, email
  • at “edge of network”client/serverpeer-peer
• client/server model
  • client host requests, receives service from always-on server
  • e.g. Web browser/server;email client/server
• peer-peer model:
  • minimal (or no) use ofdedicated servers
  • e.g. Skype, Bit Torrenth

第15页：网络边缘可靠数据传输服务

网络边缘可靠数据传输服务

• handshaking:setup(prepare for) datatransfer ahead of time
  • Hello, hello back human protocol
  • set up “state”in twocommunicating hosts
• TCP-Transmission Control Protocol
  • Internet’s reliable datatransfer service TCP service[RFC 793]
• reliable, in-orderbyte-stream data transfer
  • loss: acknowledgementsand retransmissions
• flow control:
  • sender won’t overwhelm receiver
• congestion control:
  • senders “slow down sendingrate” when network congested

第16页：Network edge: best effort (unreliable)

Network edge: best effort (unreliable)

• same as before!
• UDP-User Datagram Protocol [RFC 768]:
  • connectionless
  • unreliable datatransfer
  • no flow control
  • no congestion control App’s using TCP:
• HTTP (Web), FTP (filetransfer), Telnet(remote login), SMTP(email)App’s using UDP:
• streaming media,teleconferencing, DNS, Internet telephony

第17页：接入网和物理媒体

接入网和物理媒体

• residential access nets
• institutional access networks (school,company)
• mobile access networks Keep in mind:
• bandwidth (bits persecond) of access network?
• shared or dedicated?

第18页：住宅接入点对点接入

住宅接入点对点接入

• Dialup via modem
  • up to 56 Kbps direct access torouter (often less)
  • Can’t surf and phone at sametime: can’t be“always on”
• DSL:digital subscriber line
  • deployment: telephone company (typically)
  • 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

第19页：住宅接入电缆调制解调器

住宅接入电缆调制解调器

• HFC: hybrid fiber coax
  • asymmetric: up to 30 Mbps downstream, 2 Mbps upstream
• networkof cable and fiber attaches homes to ISP router
  • homes share access to router
• deployment: available via cable TV companies

第20页：住宅接入电缆调制解调器

住宅接入电缆调制解调器

Residential access: cable modems Diagram:

第21页：电缆网络体系结构概述

电缆网络体系结构概述

Cable Network Architecture: Overviewhome cable headendcable distribution network (simplified)Typically 500 to 5,000 homes

第22页：电缆网络体系结构概述

电缆网络体系结构概述

Cable Network Architecture: Overviewhome cable headendcable distribution network server(s)

第23页：电缆网络体系结构概述

电缆网络体系结构概述

Cable Network Architecture: Overviewhome cable headendcable distribution network (simplified)

第24页：电缆网络体系结构概述

电缆网络体系结构概述

Cable Network Architecture: Overviewhome cable headendcable distribution network Channels VIDEO VIDEO VIDEO VIDEO VIDEO VIDEODATADATA CONTROL123456789FDM (more shortly):

第25页：企业接入本地区域网络

企业接入本地区域网络

• company/univlocal areanetwork(LAN) connectsend system to edge router
• Ethernet:
  • 10 Mbs, 100 Mbps,1 Gbps, 10 Gbps Ethernet
  • modern configuration:end systems connectinto Ethernet switch
• LANs: chapter 5

第26页：无线接入网

无线接入网

• shared wireless access network connects end systemto router
  • via base station aka “access point”
• wireless LANs:
  • 802.11 b/g (Wi Fi): 11 or 54 Mbps
• wider-area wireless access
  • provided by telco operator
  • ~1 Mbps over cellular system(EVDO, HSDPA)
  • next up (?): Wi MAX (10’s Mbps)over wide areabase station mobilehosts router

第27页：家庭网络典型家庭网络组成

家庭网络典型家庭网络组成

• DSL or cable modem
• router/firewall/NAT
• Ethernet
• wireless access point wireless access point wireless laptops router/firewall cable modemto/fromcableheadend Ethernet

第28页：物理媒体

物理媒体

• Bit:propagates between transmitter/rcvr pairs
• physical link:what liesbetween 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 copperwires
  • Category 3: traditional phone wires, 10 Mbps Ethernet
  • Category 5:100 Mbps Ethernet

第29页：物理媒体同轴电缆光纤 Coaxial cable

物理媒体同轴电缆光纤 Coaxial cable

• two concentric copper conductors
• bidirectional
• baseband:
  • single channel on cable
  • legacy Ethernet
• broadband:
  • multiple channels oncable
  • HFCFiber optic cable:
• glass fiber carrying light pulses, each pulse a bit
• high-speed operation:
  • high-speed point-to-point transmission (e.g., 10’s-100’s Gps)
• low error rate: repeaters spaced far apart ; immuneto electromagnetic noise

第30页：物理媒体无线电

物理媒体无线电

• signal carried inelectromagnetic 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)
  • 11 Mbps, 54 Mbps
• wide-area(e.g., cellular)
  • 3G cellular: ~ 1 Mbps
• satellite
  • Kbps to 45 Mbps channel (ormultiple smaller channels)
  • 270 msec end-end delay
  • geosynchronous versus lowaltitude

第31页：第1章路线图

第1章路线图

• 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

第32页：网络核心

网络核心

• mesh of interconnected routers
• thefundamental question:how is data transferred through net?
  • circuit switching:dedicated circuit percall: telephone net
  • packet-switching:datasent thru net indiscrete “chunks”

第33页：网络核心电路交换 End-end

网络核心电路交换 End-end

• link bandwidth, switch capacity
• dedicated resources:no sharing
• circuit-like(guaranteed)performance
• call setup required

第34页：网络核心电路交换网络

网络核心电路交换网络

• pieces allocated to calls
• resource pieceidleifnot used by owning call(no sharing)
• dividing link bandwidthinto “pieces”
  • frequency division
  • time division

第35页：电路交换 FDM 与 TDM

电路交换 FDM 与 TDM

Circuit Switching: FDM and TDMFDMfrequencytime TDMfrequencytime 4 users Example:

第36页：数值示例

数值示例

• How long does it take to send a file of 640,000 bits from host A to host B over acircuit-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!

第37页：网络核心分组交换

网络核心分组交换

• user A, B packets share network resources
• each packet uses full linkbandwidth
• resources usedas neededre source contention:
• aggregate resource demand can exceed amount available
• congestion: packets queue, wait for link use
• store and forward:packets move one hopat a time
  • Node receives complete packet before forwarding Bandwidth division into “pieces”Dedicated allocation Resource reservation

第38页：分组交换统计复用

分组交换统计复用

Packet Switching: Statistical Multiplexing 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. ABC100 Mb/s Ethernet 1.5 Mb/s DEstatistical multiplexing queue of packets waiting for outputlink

第39页：Packet-switching: store-and-forward

Packet-switching: store-and-forward

• takes L/R seconds totransmit (push out)packet of L bits on tolink at R bps
• store and forward:entire packet mustarrive at router beforeit can be transmittedon next link
• delay = 3L/R (assumingzero propagation delay)Example:
• L = 7.5 Mbits
• R = 1.5 Mbps
• transmission delay = 15 sec RRRLmore on delay shortly …

第40页：分组交换对比电路交换

分组交换对比电路交换

• 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 activeat same time is lessthan .0004 Packet switching allows more users to use network!N users 1 Mbps link Q: how did we get value 0.0004?

第41页：分组交换对比电路交换

分组交换对比电路交换

• 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)Is packet switching a “slam dunk winner?”Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

第42页：因特网结构网络的网络

因特网结构网络的网络

• 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 ISPTier 1 ISPTier 1 ISPTier-1 provider sinter connect(peer)privately

第43页：Tier-1 ISP: e.g., Sprint…to/from

Tier-1 ISP: e.g., Sprint…to/from

Tier-1 ISP: e.g., Sprint…to/from customer speeringto/from backbone….………POP: point-of-presence

第44页：因特网结构网络的网络

因特网结构网络的网络

• “Tier-2” ISPs: smaller (often regional) ISPs
  • Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISPTier 1 ISPTier 1 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISP paystier-1 ISP forconnectivity torest of Internet
• tier-2 ISP iscustomeroftier-1 provider Tier-2 ISPsalso peerprivately witheach other.

第45页：因特网结构网络的网络

因特网结构网络的网络

• “Tier-3” ISPs and local ISPs
  • last hop (“access”) network (closest to end systems)Tier 1 ISPTier 1 ISPTier 1 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPlocal ISPlocal ISPlocal ISPlocal ISPlocal ISPTier 3ISPlocal ISPlocal ISPlocal ISPLocal and tier-3 ISPs arecustomersofhigher tier ISPsconnectingthem to restof Internet

第46页：因特网结构网络的网络

因特网结构网络的网络

• a packet passes through many networks!Tier 1 ISPTier 1 ISPTier 1 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPlocal ISPlocal ISPlocal ISPlocal ISPlocal ISPTier 3ISPlocal ISPlocal ISPlocal ISP

第47页：第1章路线图

第1章路线图

• 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

第48页：do loss and delay occur?packets

do loss and delay occur?packets

• packet arrival rate to link exceeds output linkcapacity
• packets queue, wait for turn ABpacket being transmitted(delay)packets queueing(delay)free (available) buffers: arriving packets dropped (loss) if no free buffers

第49页：分组时延的四种来源

分组时延的四种来源

• 1. nodal processing:
  • check bit errors
  • determine output link ABpropagation transmission nodal processing queueing
• 2. queueing
  • time waiting at outputlink for transmission
  • depends on congestion level of router

第50页：Delay packet-switched networks 3

Delay packet-switched networks 3

• R=link bandwidth (bps)
• L=packet length (bits)
• time to send bits intolink = L/R4. Propagation delay:
• d = length of physical link
• s = propagation speed inmedium (~2 x 108 m/sec)
• propagation delay = d/s ABpropagation transmission nodal processing queueing Note:s and R arevery different quantities!

第51页：车队类比

车队类比

• cars “propagate” at 100 km/hr
• toll booth takes 12 sec toservice car (transmissiontime)
• car~bit; caravan ~ packet
• Q: How long until caravanis lined up before 2 nd tollbooth?
• Time to “push” entire caravan through tollbooth onto highway =12*10 = 120 sec
• Time for last car topropagate from 1 st to 2 nd toll both:100 km/(100 km/hr)= 1 hr
• A: 62 minutes tollbooth tollboothten-carcaravan 100 km 100 km

第52页：车队类比补充

车队类比补充

• Cars now “propagate” at 1000 km/hr
• Toll booth now takes 1 min to service a car
• Q:Will cars arrive to 2 nd booth before allcars serviced at 1 stbooth?
• Yes!After 7 min, 1 st carat 2 nd booth and 3 carsstill at 1 st booth.
• 1 st bit of packet canarrive at 2 nd router before packet is fully transmitted at 1 st router!
  • See Ethernet applet at AWLWeb site tollbooth tollboothten-carcaravan 100 km 100 km

第53页：结点时延

结点时延

• 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

第54页：排队时延（再讨论）

排队时延（再讨论）

• R=link bandwidth (bps)
• L=packet length (bits)
• a=average packet arrival ratetraffic intensity = La/R
• La/R ~ 0: average queueing delay small
• La/R-> 1: delays become large
• La/R > 1: more “work” arriving than can beserviced, average delay infinite!

第55页：真实因特网时延与路由

真实因特网时延与路由

• What do “real” Internet delay & loss look like?
• Trace route program:provides delay measurement from source to router along end-end Internet path towards destination. For alli:
  • sends three packets that will reach routerion pathtowards destination
  • routeriwill return packets to sender
  • sender times interval between transmission and reply.3 probes 3 probes 3 probes

第56页：真实因特网时延与路由1

真实因特网时延与路由1

“Real” Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border 1-rt-fa 5-1-0.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 jn 1-at 1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn 1-so 7-0-0-0.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 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de 2-1.de 1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr 1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr 1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n 2.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 r 3 t 2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r 3 t 2.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 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 mstrace route:gaia.cs.umass.edu to www.eurecom.fr Three delay measurements fromgaia.cs.umass.edu to cs-gw.cs.umass.edu*means no response (probe lost, router not replying)trans-oceani clink

第57页：分组丢失

分组丢失

• queue (aka buffer) preceding link in buffer hasfinite capacity
• packet arriving to full queue dropped (aka lost)
• lost packet may be retransmitted by previousnode, by source end system, or not at all ABpacket being transmitted packet arriving tofull bufferislostbuffer(waiting area)

第58页：吞吐量

吞吐量

• throughput:rate (bits/time unit) at whichbits transferred between sender/receiver
  • instantaneous:rate at given point in time
  • average:rate over long(er) period of timeserver, withfile of F bitsto send to clientlink capacity Rsbits/seclink capacity Rcbits/secpipe that can carry fluid at rate Rsbits/sec)pipe that can carry fluid at rate Rcbits/sec)server sends bits(fluid) into pipe

第59页：吞吐量补充

吞吐量补充

• Rs< Rc What is average end-end throughput?Rsbits/sec Rcbits/sec
• Rs> Rc What is average end-end throughput?Rsbits/sec Rcbits/seclink on end-end path that constrains end-end throughput bottleneck link

第60页：Throughput: Internet scenario 10

Throughput: Internet scenario 10

• per-connectionend-endthroughput:min(Rc, Rs, R/10)
• in practice: Rcor Rsis often bottleneck

第61页：第1章路线图

第1章路线图

• 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

第62页：Protocol “Layers”Networks complex!

Protocol “Layers”Networks complex!

• many “pieces”:
  • hosts
  • routers
  • links of various media
  • applications
  • protocols
  • hardware,software Question:Is there any hope oforganizingstructure ofnetwork?Or at least our discussionof networks?

第63页：Organization air travel

Organization air travel

• a series of stepsticket (purchase)baggage (check)gates (load)runway takeoff airplane routing ticket (complain)baggage (claim)gates (unload)runway landing airplane routing airplane routing

第64页：ticket (purchase)baggage (check)gates

ticket (purchase)baggage (check)gates

• via its own internal-layer actions
• relying on services provided by layer below

第65页：layering?Dealing with complex systems

layering?Dealing with complex systems

• explicit structure allows identification,relationship of complex system’s pieces
  • layered reference modelfor discussion
• modularization eases maintenance, updating ofsystem
  • change of implementation of layer’s service transparent to rest of system
  • e.g., change in gate procedure doesn’t affectrest of system
• layering considered harmful?

第66页：因特网协议栈

因特网协议栈

• application:supporting network applications
  • FTP, SMTP, HTTP
• transport:process-process datatransfer
  • TCP, UDP
• network:routing of datagrams fromsource to destination
  • IP, routing protocols
• link:data transfer between neigh boring network elements
  • PPP, Ethernet
• physical:bits “on the wire”application transport networklink physical

第67页：ISO/OSI reference model

ISO/OSI reference model

• presentation:allow applications tointerpret meaning of data, e.g.,encryption, compression, machine-specific conventions
• session:synchronization,checkpointing, recovery of dataexchange
• Internet stack “missing” these layers!
  • these services,if needed,mustbe implemented in application
  • needed?application presentation session transport networklink physical

第68页：源应用运输网络

源应用运输网络

source application transport networklink physical Ht Hn Msegment Htdatagram destination application transport networklink physical Ht Hn Hl MHt Hn MHt MMnetworklinkphysicallinkphysical Ht Hn Hl MHt Hn MHt Hn MHt Hn Hl Mrouter switch Encapsulation message MHt MHnframe

第69页：第1章路线图

第1章路线图

• 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

第70页：网络安全

网络安全

• attacks on Internet infrastructure:
  • infecting/attacking hosts: malware, spyware,worms, unauthorized access (data stealing, useraccounts)
  • 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 trustingusers attached to a transparent network”
  • Internet protocol designers playing “catch-up”
  • Security considerations in all layers!

第71页：什么可 bad guys 恶意软件

什么可 bad guys 恶意软件

• Spyware:
  • infection by downloadingweb page with spyware
  • records keystrokes, websites visited, upload infoto collection site
• Virus
  • infection by receivingobject (e.g., e-mailattachment), activelyexecuting
  • self-replicating:propagate itself toother hosts, users
• Worm:
  • infection by passivelyreceiving object that getsitself executed
  • self-replicating: propagatesto other hosts, users Sapphire Worm: aggregate scans/secin first 5 minutes of outbreak (CAIDA, UWisc data)

第72页：拒绝服务攻击

拒绝服务攻击

• attackers make resources (server, bandwidth)unavailable to legitimate traffic by overwhelmingre source with bogus traffic 1.select target 2.break into hostsaround the network(see malware)3.send packets toward target fromcompromised hoststarget

第73页：Sniff, modify, delete your packets

Sniff, modify, delete your packets

• broadcast media (shared Ethernet, wireless)
• promiscuous network interface reads/records allpackets (e.g., including passwords!) passing by ABCsrc:B dest:A payload
• Ethereal software used for end-of-chapter labsis a (free) packet-sniffer
• more on modification, deletion later

第74页：Masquerade you

Masquerade you

• IP spoofing:send packet with false source address ABCsrc:Bdest:A payload

第75页：Masquerade you

Masquerade you

• IP spoofing:send packet with false source address
• record-and-playback: sniff sensitive info (e.g.,password), and use later
  • password holderisthat user from system point ofview ABCsrc:B dest:A user: B; password: foo

第76页：Masquerade you

Masquerade you

• IP spoofing:send packet with false source address
• record-and-playback: sniff sensitive info (e.g.,password), and use later
  • password holderisthat user from system point ofview ABlater ….. Csrc:B dest:A user: B; password: foo

第77页：网络安全

网络安全

• more throughout this course
• chapter 8: focus on security
• crypographic techniques: obvious uses andnot so obvious uses

第78页：第1章路线图

第1章路线图

• 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

第79页：因特网发展历史

因特网发展历史

• 1961:Kleinrock-queueing theory shows effectiveness of packet-switching
• 1964:Baran-packet-switching in military nets
• 1967:ARPAnet conceivedby 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 1961-1972: Early packet-switching principles

第80页：因特网发展历史

因特网发展历史

• 1970:ALOHAnet satellite network in Hawaii
• 1974:Cerf and Kahn-architecture forinter connecting networks
• 1976:Ethernet at Xerox PARC
• ate 70’s:proprietary architectures: DECnet, SNA, XNA
• late 70’s:switching fixed length packets (ATMprecursor)
• 1979:ARPAnet has 200 nodes Cerf and Kahn’s inter networking principles:
  • minimalism, autonomy-nointernal changes requiredto interconnect networks
  • best effort service model
  • stateless routers
  • decentralized control define today’s Internet architecture 1972-1980: Inter networking, new and proprietary nets

第81页：因特网发展历史

因特网发展历史

• 1983:deployment of TCP/IP
• 1982:smtp e-mailprotocol defined
• 1983:DNS definedfor name-to-IP-address translation
• 1985:ftp protocol defined
• 1988:TCP congestion control
• new national networks:Csnet, BITnet, NSFnet, Minitel
• 100,000 hostsconnected toconfederation ofnetworks 1980-1990: new protocols, a proliferation of networks

第82页：因特网发展历史

因特网发展历史

• Early 1990’s:ARPAnetde commissioned
• 1991:NSF lifts restrictions oncommercial use of NSFnet(decommissioned, 1995)
• early 1990 s:Web
  • hypertext [Bush 1945, Nelson 1960’s]
  • HTML, HTTP: Berners-Lee
  • 1994: Mosaic, later Netscape
  • late 1990’s:commercializationof the Web Late 1990’s
  • 2000’s:
• more killer apps: instantmess aging, P2P file sharing
• network security toforefront
• est. 50 million host, 100 million+ users
• backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps

第83页：因特网发展历史2007

因特网发展历史2007

• ~500 million hosts
• Voice, Video over IP
• P2P applications: Bit Torrent(file sharing) Skype (Vo IP), PPLive (video)
• more applications: You Tube,gaming
• wireless, mobility

第84页：本章小结

本章小结

• 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, detailtofollow!