OSI and TCP Reference Models RD-CSY10171

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

 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

mail server user agent user agent user agent mail server user agent user agent mail server user agent RD-CSY10175

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

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

Number of Hosts on the Internet: Aug Oct ,024 Dec ,174 Oct ,000 Jul ,776,000 Jul ,540,000 Jul ,218,000 Jul ,139,000 Jul ,284,000 Jul ,774,000 Jul ,937,000 Jan ,226,000 RD-CSY10178

 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

 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

 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

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

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

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

 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

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