1. OSI and TCP Reference Models RD-CSY10171

2.  To understand  Basic definitions  Protocol  Application  Understand communication process using Reference models ◦ OSI Reference Model ◦ TCP/IP - Internet Model RD-CSY10172

3.  A network protocol defines the ◦ format and the order of messages ◦ exchanged between two or more communicating entities, as well as the ◦ actions taken on the transmission and/or receipt of a message or other events. RD-CSY10173

5. mail server user agent user agent user agent mail server user agent user agent mail server user agent RD-CSY10175

6. Messages format and order  From a client to a mail server ◦ HELO ◦ MAIL FROM: ◦ RCPT TO: ◦ DATA ◦ QUIT  From a mail server to a client ◦ status code  1xx - Informative message  2xx - Command ok  3xx - Command ok so far, send the rest of it.  4xx - Command was correct, but couldn't be performed for some reason.  5xx - Command unimplemented, or incorrect, or a serious program error occurred. ◦ content user mailbox outgoing message queue mail server user agent user agent user agent mail server user agent user agent mail server user agent SMTP POP3, IMAP SMTP RD-CSY10176

7. Network Applications are Programs that run on different end systems and communicate over a network. applicati on transpor t network data link physical applicati on transpor t network data link physical applicati on transpor t network data link physical 7

8. Number of Hosts on the Internet: Aug. 1981 213 Oct. 1984 1,024 Dec. 1987 28,174 Oct. 1990 313,000 Jul. 1993 1,776,000 Jul. 1996 19,540,000 Jul. 1999 56,218,000 Jul. 2004 285,139,000 Jul. 2005 353,284,000 Jul. 2007 489,774,000 Jul. 2008 570,937,000 Jan. 2009 625,226,000 RD-CSY10178

9.  All standards of the Internet are published as RFC (Request for Comments)  e.g., the SMTP protocol is specified in RFC821  A typical (but not the only) way of standardization:  Internet draft  RFC  proposed standard  draft standard (requires 2 working implementations)  Internet standard (declared by Internet Architecture Board) We reject: kings, presidents, and voting. We believe in: rough consensus and running code. RD-CSY10179

10.  Why need standards?  The use of standards in protocols ensures that products from different manufacturers can work together  Do you know of name of a standards body for : ◦ food industry  FSA ◦ Computer Science and Engineering  IEEE  And many others 10

11.  The problem of moving information between computers over a network medium is divided into smaller and more manageable problems  This separation into smaller more manageable functions is known as layering.  Two Reference Models: ◦ OSI -7 Layer Model ◦ TCP/IP Model  Also known as the Internet model RD-CSY101711

12. RD-CSY1017 여보세요 She is saying hello Ambassador in Korea Translator Secretary The Korean ambassador said “Hello” Bonjour! Ambassador in France Translator Secretary 12

13. RD-CSY1017 A standard reference model called OSI (Open Systems Interconnect ) is now considered the primary Architectural model for inter-computer communications The OSI model divides the networking process into seven layers. Each layer in the model has a unique function in the communication process and communicates with the layer directly above and below it. OSI Model Application Presentation Session Transport Network Data Link Physical 13

14. RD-CSY1017 Information passed from source to destination has to pass through each layer on each side. Which layer does the user interact with: Application or Physical ? Which layers are connected by a cable? 14

15.  Phrase to remember 7 layers is: All People Seem To Need Data Processing  What is a protocol?  Examples of some network applications?  Need for standardisation?  Example of a standard?  How many layers in OSI model? RD-CSY101715

16.  Physical Layer ◦ Media ◦ Topology ◦ Making Cables RD-CSY101716