操作系統(tǒng)課件第六章

1、Copyright © Xu Jingdong, All right reserved,1,Computer Networks review,Xu Jingdong Dept. of Computer Science and Information Security Nankai University xujd@nankai.edu.cn,Copyright © Xu Jingdong, All right

2、 reserved,2,Chapter 1,Internet overviewnetwork edge: client/server and peer-to-peer modelnetwork core: packet-switching versus circuit-switchingpacket-switchingstatistical multiplexingroutingend to end latencymess

3、age and packetProtocol, layering and service modelsWhy layeringOSI reference model, TCP/IP modellogical communication, physical communication,Copyright © Xu Jingdong, All right reserved,3,Chapter 2,Application s

4、ervice requirements:reliability, bandwidth, delayInternet transport service modelconnection-oriented, reliable: TCPunreliable, datagram: UDPClient-server, P2PFile Transfer Service and Protocol FTP Process ModelFT

5、P commands and responsesConnection and Authorization,Copyright © Xu Jingdong, All right reserved,4,Chapter 2 (cont.),Web Service and ProtocolWeb Client/server ModeBrowser ArchitectureHTTP: HyperText Transfer Pro

6、tocol-1.0 and 1.1Uniform Resource LocatorsHyperText Markup LanguageElectronic Mail Service and ProtocolMail Client/server ModeSimple Mail Transfer ProtocolMail access protocols-POP3Mail Message Format-822 and MIME

7、,Copyright © Xu Jingdong, All right reserved,5,Chapter 2 (cont.),DNSFlat and Hierarchical NamespaceDNS Name SpaceName ResolutionResource Record StructureDNS Message FormatWireshark,Copyright © Xu Jingdong

8、, All right reserved,6,Chapter 3,Transport layer servicesMultiplexing/demultiplexingConnectionless transport: UDPPrinciples of reliable data transferrdt1.0, rdt2.0, rdt2.1, rdt2.2, rdt3.0Performance of protocolstop

9、-and-wait protocolpipelined protocols: Go-Back-N and Selective Repeat,Copyright © Xu Jingdong, All right reserved,7,Chapter 3 (cont.),Connection-oriented transport: TCPreliable transfer seq. # and ACK # Timeouts

10、 and Retransmission, Fast Retransmit flow controlconnection managementTCP congestion controlcongestion windowslow startcongestion avoidance: Tahoe and Renofast recovery,Copyright © Xu Jingdong, All right rese

11、rved,8,Chapter 4,Internet protocol (IP)IP addressingIP datagram formatIP datagram forwardingIP Fragmentation & ReassemblyForwarding in an IP RouterSubnetting and CIDRNAT: Network Address TranslationInternet C

12、ontrol Message Protocol (ICMP),Copyright © Xu Jingdong, All right reserved,9,Chapter 4 (cont.),routing principleslink state algorithmsdistance vector algorithmshierarchical routingInternet routing protocolsintr

13、a-domain: RIP, OSPF Inter-domain: BGP,Copyright © Xu Jingdong, All right reserved,10,Chapter 5,Introduction of interface layerBroadcast vs. Switched NetworksLAN architecture and Interface Layer functions Princip

14、les of interface layerEncoding and decodingError detectionMultiple access protocols: CSMA/CDLAN technologies LAN addressing: physical addressMapping IP address to physical address: ARPShared EthernetSwitched Ethe

15、rnet,,,HTTP request sent into TCP socket,IP datagram containing HTTP request routed to www.google.com,IP datagram containing HTTP reply routed back to client,,64.233.169.105,web server,,web server responds with HTTP repl

16、y (containing web page),web page finally (!!!) displayed,11,,,ISP network 68.80.0.0/13,,,,,,,,,Google’s network 64.233.160.0/19,,64.233.169.105,web server,DNS server,school network 68.80.2.0/24,web page,,,,,,,,,,12,co

17、nnecting laptop needs to get its own IP address, addr of first-hop router, addr of DNS server: use DHCP,,DHCP request encapsulated in UDP, encapsulated in IP, encapsulated in 802.3 Ethernet,Ethernet frame broadcast (dest

18、: FFFFFFFFFFFF) on LAN, received at router running DHCP server,Ethernet demuxed to IP demuxed, UDP demuxed to DHCP,13,encapsulation at DHCP server, frame forwarded (switch learning) through LAN, demultiplexing at client,

19、Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router,DHCP client receives DHCP ACK reply,DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-

20、hop router for client, name & IP address of DNS server,14,before sending HTTP request, need IP address of www.google.com: DNS,,DNS query created, encapsulated in UDP, encapsulated in IP, encapsulated in Eth. To sen

21、d frame to router, need MAC address of router interface: ARP,ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface,client now knows MAC address of first hop router,

22、so can now send frame containing DNS query,15,,,IP datagram containing DNS query forwarded via LAN switch from client to 1st hop router,IP datagram forwarded from campus network into comcast network, routed (tables creat

23、ed by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server,demux’ed to DNS serverDNS server replies to client with IP address of www.google.com,ISP network 68.80.0.0/13,,DNS server,16,,,to send HTTP request, cl

24、ient first opens TCP socket to web server,TCP SYN segment (step 1 in 3-way handshake) inter-domain routed to web server,TCP connection established!,,64.233.169.105,web server,,,web server responds with TCP SYNACK (step 2

25、 in 3-way handshake),17,,,HTTP request sent into TCP socket,IP datagram containing HTTP request routed to www.google.com,IP datagram containing HTTP reply routed back to client,,64.233.169.105,web server,,web server resp