1. Fetching a Web Page www.si.umich.edu Home computer The Internet

2. Fetching a Web Page www.si.umich.edu Home computer The Internet MichNet Modem

3. Networks Overview Communication Links

4. Networks Overview Communication Links Internetworking (IP)

5. Networks Overview Communication Links Internetworking (IP) TCP and HTTP Quality of Service

6. Internet protocol (IP) Subnetworks User datagram protocol (UDP) Transmission control protocol (TCP) HyperText Transport Protocol (HTTP) Application Real-time transport protocol (RTP) Internet protocols

7. Hosts Switches/Routers Backbone links Access links Internet Topology

8. Tracert si.umich.edu 1 * Request timed out. 2 140 ms 207.75.186.1 3 140 ms f-umbin.c-ccb2.umnet.umich.edu [198.108.3.5] 4 240 ms f-backbone.c-ugli.umnet.umich.edu [141.211.0.9] 5 141 ms bart.si.umich.edu [141.211.203.32]

9. Fetching a Web Page www.si.umich.edu Home computer MichNet Modem 207.75.186.1 198.108.3.5 141.211.0.9 141.211.203.32 c-ccb2 router c-ugli router

10. IP Network 1Network 2 TCP or UDP Host AHost B ORB Application Switch N 2N 1 IIOP IP as Spanning Layer

11. Gateway Public telephone network Internet Computer w/modem    IP over Voice Computer w/modem

12. Gateway Public telephone network Internet IP telephone Plain old telephone    Voice over IP

13. Hosts Switches/Routers Backbone links Access links Interconnection Pricing Peers Providers

14. Local Namespaces NS Hosts si.umich.edu NS eecs.umich.edu umich.edu NS “root” Nameserver

15. Original packet Divide into packet fragments New packets Reassembled original packet HeaderPayload

16. Layer n+1 Layer n Layer n+1 protocol header Layer n protocol header Encapsulated layer n+1 packet, including header Peer-to-peer operation

17. HTTP Service Client can make requests –GET, POST (some others) Server responds –HTTP headers –HTML document or JPEG, or GIF, or…

18. URL Structure :// : / Scheme –HTTP, FTP, GOPHER, MAILTO,... Host –An IP address or DNS name

19. HTTP example When a browser fetches http://www.si.umich.edu/~presnick/ –http:// says to use HTTP protocol –Resolve www.si.umich.edu in DNS 141.211.203.34 –Make TCP connection 141.211.203.34, port 80 –Send the following text string GET /~presnick/ HTTP/1.1 Host: www.si.umich.edu

20. Server sends back HTTP/1.1 200 OK Date: Mon, 22 Dec 1997 15:12:32 GMT Server: Apache/1.2.4 Last-Modified: Thu, 04 Dec 1997 16:26:10 GMT ETag: "5f2f2-33fd-3486d9a2" Content-Length: 13309 Accept-Ranges: bytes Connection: close Content-Type: text/html ….

21. HTML Paul Resnick Associate Professor University of Michigan School of Information 314 West Hall 550 East University Avenue Ann Arbor, MI 48109-1092 presnick@umich.edu