1Network Architecture ModelsSchool of BusinessEastern Illinois University © Abdou Illia, Spring 2007(Week 2, Thursday 1/18/2007)2Learning Objectives Discuss the OSI reference Model Discuss the Internet Model Compare OSI and Internet Models3Data Networks operation Packet Switching– Large messages are broken into small pieces called packets (or frames) Multiplexing– Packets from many conversations are mixed (multiplexed) over each trunk lineMultiplexing onTransmission LinePacket Switching24Why Packet Switching & Multiplexing? Switches, routers, bridges handle short messages efficiently Sending a file all in one single string of data:– Other computers couldn’t use the Network during transmission– Not be appreciated by other users– If error, the entire file have to be sent again5How computers make sense of incoming packets? Rules of operation defined through:– Network Architecture Models– Protocols, i.e.: Rules for communications between 2 computers (or other networking devices) implemented in hardware or in software.6Network Architecture Model? A communication model that define specific tasks that together allow applications on different computers to communicateComputer 1Task 1Task 2Task 3Task 4Task 5Task 1Task 2Task 3Task 4Task 5Computer 237Network Architecture Model? A communication model that describe how data from a software application in one computer moves through a medium to a software application in another computer.Computer 1Task 1Task 2Task 3Task 4Task 5Task 1Task 2Task 3Task 4Task 5Computer 2RulesRulesRulesRules8Network Architecture Model Two main components:– Layers (representing groups of tasks to be performed for data comm.)– Protocols (representing rules to be followed) Examples of network architecture models:– OSI Reference Model– Internet Model (or TCP/IP Model)– Hybrid TCP/IP-OSI Model9OSI Reference Model Deals with connecting Open Systems:– Systems opened for communication with other systems– Non-proprietary systems (e.g. IBM’s Systems Network Architecture )First step toward international standardization The other Network architectures roughly follow the OSI structure410Principles guiding OSI development Create a layer when a different level of abstraction is needed Each layer should perform a well defined function Choose function of layers with an eye toward defining international protocols Choose layers’ boundaries in order to minimize information flow across interfaces.11OSI Reference Model 7 layers Each layer communicates with its peer layer, and with layer above and below it. Different protocols at each layer Upper layer deal with application issues, and are implemented in software Lower layers handle data transport issues, and are implemented in software and hardwareApplicationData transport12OSI Reference Model7. Application6. Presentation5. Session4. Transport3. Network2. Data Link1. Physical513OSI Reference ModelLayers RoleApplication • Represent user interface between the application sofware (e.g. Eudora) and the Network• Provides services like: Identification of the intended communication partner, determining resources availability for communication, etc.7Presentation • Performs code conversion and data reformatting (syntax translation) incluing encryption and compression if required.• Uses coding & conversion schemes: Common Data Representation Formats, Common Data Encryption Schemes, EBCDIC, ASCII, etc.6Session• Responsible for establishing, managing & terminating communication sessions between computers.• Communication sessions consist of service requests and service responses between applications • Session layer’s protocols coordinate request & response sessions.514OSI Reference ModelLayers RoleTransport• Makes sure the data arrives at the destination exactly as it left source (in case of connection-oriented communication)• Provides error checking before transmission, and error recovery in case of failed delivery.4Network• Responsible for creating, maintaining and ending network connections. • Provides logical address (IP address) to messages• Provides routing services: determining routes for sending. If router can’t send large packets, break data into smaller units.3• Subdivided into 2 sublayers (Logical Link Control and Media Access Control)• Provides physical address (MAC address) to messages• Combines bits into bytes, bytes into a frames with header, address information, error detection code, and trailer2DataLinkLLCMAC15OSI Reference ModelLayers RolePhysical• Handles the transmission of bits over a communications channel.• Defines characteristics such as voltage levels, connector types and maximum transmission distance.• Places signal on the cable. Responsible to move bits between devices.1616The Internet Model (TCP/IP Model) Created by the Internet Engineering Task Force (IETF) Named after its two most widely known protocols:– TCP (Transmission Control Protocol) and – IP (Internet Protocol) TCP/IP refer to the model, while TCP and IP are individual protocols17The Internet ModelPhysicalData LinkNetworkTransportSessionPresentationApplication 4 layers Interface layer - equivalent to the OSI’s Physical and Data link layers Network layer - roughly equivalent to the OSI’s Network layer Transport layer - performs same function as OSI Transport layer Application layer - equivalent to the OSI’s Presentation and Application layersInterfaceNetworkTransportApplicationOSI InternetFigure 1-14 (White 2002:19)18Applications/Protocols Use in Internet Model• PPP (Point-to-Point Protocol)• V.90 for 56 Kbps modemsInterface• IP (Internet Protocol)Network• TCP (Transmission Control Protocol). • Required in webservice when HTTP is used• Required in Mailservice when SMTP is used. SMTP messages are encapsulated in TCP segments• Connection-oriented: Establishes and maintains connections before sending. Close connections after transmission. Correct errors in TCP segments.• UDP (User Datagram Protocol)• Connectionless: Don’t open connection. Simply sends. Discards incorrect UDP datagrams (no retransmission)Transport• Webservice: HTTP• E-mail: SMTP (Simple Mail Transfer Protocol), POP (PostOffice Protocol), IMAP (Internet Message AccessProtocol)• Telnet applications: Terminal Emulation Protocol• File transfer: