操作系统课件第六章

1、Copyright Xu Jingdong, All right reserved,1,Computer Networks review,Xu Jingdong Dept. of Computer Science and Information Security Nankai University ,Copyright Xu Jingdong, All right reserved,2,Chapter 1,Internet overview network edge: client/server and peer-to-peer model network core: packet-switc

2、hing versus circuit-switching packet-switching statistical multiplexing routing end to end latency message and packet Protocol, layering and service models Why layering OSI reference model, TCP/IP model logical communication, physical communication,Copyright Xu Jingdong, All right reserved,3,Chapter

3、 2,Application service requirements: reliability, bandwidth, delay Internet transport service model connection-oriented, reliable: TCP unreliable, datagram: UDP Client-server, P2P File Transfer Service and Protocol FTP Process Model FTP commands and responses Connection and Authorization,Copyright X

4、u Jingdong, All right reserved,4,Chapter 2 (cont.),Web Service and Protocol Web Client/server Mode Browser Architecture HTTP: HyperText Transfer Protocol-1.0 and 1.1 Uniform Resource Locators HyperText Markup Language Electronic Mail Service and Protocol Mail Client/server Mode Simple Mail Transfer

5、Protocol Mail access protocols-POP3 Mail Message Format-822 and MIME,Copyright Xu Jingdong, All right reserved,5,Chapter 2 (cont.),DNS Flat and Hierarchical Namespace DNS Name Space Name Resolution Resource Record Structure DNS Message Format Wireshark,Copyright Xu Jingdong, All right reserved,6,Cha

6、pter 3,Transport layer services Multiplexing/demultiplexing Connectionless transport: UDP Principles of reliable data transfer rdt1.0, rdt2.0, rdt2.1, rdt2.2, rdt3.0 Performance of protocol stop-and-wait protocol pipelined protocols: Go-Back-N and Selective Repeat,Copyright Xu Jingdong, All right re

7、served,7,Chapter 3 (cont.),Connection-oriented transport: TCP reliable transfer seq. # and ACK # Timeouts and Retransmission, Fast Retransmit flow control connection management TCP congestion control congestion window slow start congestion avoidance: Tahoe and Reno fast recovery,Copyright Xu Jingdon

8、g, All right reserved,8,Chapter 4,Internet protocol (IP) IP addressing IP datagram format IP datagram forwarding IP Fragmentation & Reassembly Forwarding in an IP Router Subnetting and CIDR NAT: Network Address Translation Internet Control Message Protocol (ICMP),Copyright Xu Jingdong, All right res

9、erved,9,Chapter 4 (cont.),routing principles link state algorithms distance vector algorithms hierarchical routing Internet routing protocols intra-domain: RIP, OSPF Inter-domain: BGP,Copyright Xu Jingdong, All right reserved,10,Chapter 5,Introduction of interface layer Broadcast vs. Switched Networ

10、ks LAN architecture and Interface Layer functions Principles of interface layer Encoding and decoding Error detection Multiple access protocols: CSMA/CD LAN technologies LAN addressing: physical address Mapping IP address to physical address: ARP Shared Ethernet Switched Ethernet,HTTP request sent i

11、nto TCP socket,IP datagram containing HTTP request routed to ,IP datagram containing HTTP reply routed back to client,05,web server,web server responds with HTTP reply (containing web page),web page finally (!) displayed,11,ISP network /13,Googles network /19,64.233.

12、169.105,web server,DNS server,school network /24,web page,12,connecting 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: FFFFFFF

13、FFFFF) 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,Client now has IP address, knows name & addr of DNS server, IP address of its first-hop r

14、outer,DHCP client receives DHCP ACK reply,DHCP server formulates DHCP ACK containing clients IP address, IP address of first-hop router for client, name & IP address of DNS server,14,before sending HTTP request, need IP address of : DNS,DNS query created, encapsulated in UDP, encapsulated in IP, enc

15、apsulated in Eth. To send 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, so can now send frame containing DNS query,15,IP datagra

16、m containing DNS query forwarded via LAN switch from client to 1st hop router,IP datagram forwarded from campus network into comcast network, routed (tables created by RIP, OSPF, IS-IS and/or BGP routing protocols) to DNS server,demuxed to DNS server DNS server replies to client with IP address of ,

17、ISP network /13,DNS server,16,to send HTTP request, client 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!,05,web server,web server responds with TCP SYNACK (step 2 in 3-way handshake),17,HTTP request sent into TCP soc