Transcript ppt
OSI Model Open Systems Interconnection reference model. International Organization for Standardization (1984): The model modulizes a sequence of tasks for inter-exchanged information between computers into 7 layers: • • • • • • • Application layer (7) Presentation layer (6) Session layer (5) Transport layer (4) Network layer (3) Data Link layer (2) Physical layer (1) • Each layer should be viewed as a job (task) description but not the actual rules or methods to do the job OSI Model Analogy Knight Lancelot King Arthur Secretary Secretary Servant Servant Captain Captain OSI, Peer-Layer Communication John H7 Token Ring 1. Physical Data 5 Data 7 Data 8 4. Transport 3. Network 2. Data Link 1. Physical Ethernet H6 2. Data Link Data 4 5. Session Server H5 Server 3. Network Data 3 6. Presentation Unix H4 4. Transport Data2 7. Application Netscape 5. Session Data Header1 Header2 Win 2K 6. Presentation H3 IE 7. Application Mary Packet Switching A I 1 2 Data Link Layer LOVE YOU.. I LOVE YOU.. I LOVE YOU.. I LOVE YOU! B 3 13 4 5 6 7 8 9 10 11 12 I_LO VE_Y OU.. _I_L OVE_ YOU. ._I_ LOVE _YOU .._I _LOV E_YO U!__ 1, 13 5 2 3 8 B 6 6, 4 7 A In addition to the sequence number, a packet should contain information about the sender and receiver. The packet that transmitted across the Internet is call IP Datagram. 9 7,8,11,13,1,2,9,10,5, 6,4,6,12,3 11 This can be a LAN or Internet. 10 12 Internet and Routers SU Chicago CNY Boston Yale Seattle NYC Colgate Denver SF A routers is a special purposed Computer that receives and forwards datagrams from and to the Internet. LA UCLA In fact, it is router that connects networks together. Price? $10,000,000 to $69. Houston Address Post Office as the Router Regional Post Office Local Post Office Mailman Mailman Air Port Air Port Regional Post Office Local Post Office Mailman Internet and Routers SU Chicago Boston CNY Yale Seattle NYC Colgate Colgate Denver SF Lib CS CSLab LA Houston UCLA UCLA CS at Colgate TCP/IP • • Transmission Control Protocol / Internet Protocol TCP tells how to break the information into packets. IP tells how to send packets across the Internet IP Address: (4 bytes) 256 256 256 256 = 4,294,967,296 128.10.2.1 128.230.208.46 128.230.18.55 149.43.80.141 149.43.3.23 0 0 0 0 255 255 255 255 Chung-Chih Li 48 Payne Street Hamilton, NY USA DNS Domain Name System IP address 128.10.2.1 128.230.208.46 128.230.18.55 149.43.3.23 149.43.1.7 ………….. ( some IP may not have a domain name) Domain Name arthur.cs.purdue.edu apollo.syr.edu rodan.syr.edu cs.colgate.edu colgate.edu ………….. …………. The table is huge, we don’t want to maintain this table in every computer. Domain Name Server : • A computer that provides DNS services. • One can let his/her computer uses a specific DNS or let it arbitrarily use an available one. Routers and IP Address 128.230 Chicago CNY Boston Yale Seattle NYC DNS ……….. 149.43.1.7 149.43.3.23 149.43.2.1 …………. cs.colgate.edu = 149.43.3.23 ……….. 3 Denver SF 2 DNS ……….. LA cs.colgate.edu = 149.43.3.23 ……….. 1 UCLA Houston We need a DNS to translate this domain name so the router knows how to forward the message. cs.ucla.edu/~xxx http://cs.colgate.edu/~chungli …………. 131.179.128.25 131.179.128.25/~xxx http://cs.colgate.edu/~chungli …………. Traveling trough the Internet 5 Chicago 4 128.230 6 Boston CNY Yale Seattle 7 DNS ……….. cs.colgate.edu = 149.43.3.23 ……….. 3 149.43.1.7 149.43.3.23 8 149.43.2.1 …………. Denver SF 131.179.128.25/~xxx http://cs.colgate.edu/~chungli 131.179.128.25/~xxx http://149.43.3.23/~chungli 2 DNS LA ……….. cs.colgate.edu = 149.43.3.23 ……….. 1 UCLA …………. 131.179.128.25 …………. Houston NYC Traveling trough the Internet (2) 5 Chicago 4 Seattle 128.230 6 11 3 1 12 Houston 13 UCLA …………. 131.179.128.25 14 …………. 7 NYC 149.43.1.7 149.43.3.23 8 149.43.2.1 …………. 131.179.128.25/~xxx (index.html) Denver SF LA Yale 10 9 2 Boston CNY Dynamic IP addresses home.twcny.rr.com 207.211.212.39. CNY ……………………… dennisliattwcny ……………………… …………………………. ……………………… dli : ([email protected]) seanyboy : ([email protected]) gbush : ([email protected]) ………………………….. ………………………….. twcny.rr.com 24.24.1.140 66.24.2.170 66.24.3.190 66.24.3.180 192.168.0.188 192.168.0.190 192.168.0.196