Networking Models OSI Model Created by International Organization Standardization Prepared by Agha Mohammad Haidari Network Manager ICT Directorate Ministry of Communication & IT Email : Agha.m@mcit.gov.af Cell#0700148122
OSI Model The early development of networks was disorganized in many ways. The early 1980s saw tremendous increases in the number and size of networks. As companies realized the advantages of using networking technology, networks were added or expanded almost as rapidly as new network technologies were introduced. By the mid-1980s, these companies began to experience problems from the rapid expansion. Just as people who do not speak the same language have difficulty communicating with each other, it was difficult for networks that used different specifications and implementations to exchange information. The same problem occurred with the companies that developed private or proprietary networking technologies. Proprietary means that one or a small group of companies controls all usage of the technology. Networking technologies strictly following proprietary rules could not communicate with technologies that followed different proprietary rules 2-2
OSI Model The Open System Interconnection (OSI) reference model released in 1984 was the descriptive network model that the ISO created. It provided vendors with a set of standards that ensured greater compatibility and interoperability among various network technologies produced by companies around the world. 2-3
OSI Model Dividing the network into seven layers provides the following advantages: It breaks network communication into smaller, more manageable parts. It standardizes network components to allow multiple vendor development and support. It allows different types of network hardware and software to communicate with each other. It prevents changes in one layer from affecting other layers. It divides network communication into smaller parts to make learning it easier to understand 2-4
Seven Layers of the OSI Reference Model Layer 7: Application Layer 6: Presentation Layer 5: Session Layer 4: Transport Layer 3: Network Layer 2: Data link Layer 1: Physical 2-5
Why a Layered Network Model? 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link Reduces complexity (one big problem to seven smaller ones) Standardizes interfaces Facilitates modular engineering Simplifies teaching and learning 1 Physical 2-6
Devices Function at Layers 7 Application NIC Card 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Hub 2-7
Host Layers 7 Application 6 Presentation 5 Session 4 Transport Host layers: Host layers: Provide accurate data delivery between }computers 3 Network 2 Data Link 1 Physical 2-8
Media Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical } } over Host layers: Provide accurate data delivery between computers Media layers: Control physical delivery of messages the network 2-9
Layer Functions 7 Application Provides network services to application processes (such as electronic mail, file transfer, 2-10
Layer Functions 7 Application Network services to applications 6 Presentation Data representation Ensures data is readable by receiving system Format of data Data structures Negotiates data transfer syntax for application layer 2-11
Layer Functions 7 Application 6 Presentation 5 Session Network services to applications Data representation Inter-host communication Establishes, manages, and terminates sessions between applications 2-12
Layer Functions 7 Application 6 Presentation 5 Session Network services to applications Data representation Inter-host communication 4 Transport End-to-end connection reliability Concerned with data transport issues between hosts Data transport reliability Establishes, maintains, and terminates virtual circuits Fault detection and recovery Information flow control 2-13
Layer Functions 7 Application 6 Presentation 5 Session Network services to applications Data representation Inter-host communication 4 3 Transport Network End-to-end connection reliability Addresses and best path Provides connectivity and path selection between two end systems Domain of routing 2-14
Layer Functions 7 Application 6 Presentation 5 Session Network services to applications Data representation Inter-host communication 4 3 2 Transport Network Data Link End-to-end connection reliability Addresses and best path Access to media Provides reliable transfer of data across media Physical addressing, network topology, error notification, flow control 2-15
Layer Functions 7 Application 6 Presentation 5 Session Network services to applications Data representation Inter-host communication 4 3 2 1 Transport Network Data Link Physical End-to-end connection reliability Addresses and best path Access to media Binary transmission Wires, connectors, voltages, data rates 2-16
Peer-to-Peer Communications Host A Host B 7 Application Application 6 Presentation Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Segments Packets Frames Bits Session Transport Network Data Link Physical 2-17
Data Encapsulation Host A Application Presentation Session Transport Network Data Link Physical } { Data Host B Application Presentation Session Transport Network Data Link Physical 2-18
Data Encapsulation Host A Application Presentation Session Transport Network Data Link Physical } { Network Header Data Data Host B Application Presentation Session Transport Network Data Link Physical 2-19
Data Encapsulation Host A Application Presentation Session Transport Network } { Network Header Data Data Host B Application Presentation Session Transport Network Data Link Frame Header Network Header Data Frame Trailer Data Link Physical Physical 2-20
Data Encapsulation Host A Application Presentation Session Transport Network Data Link Physical } { Frame Header Network Header Network Header Data Data Data 0101101010110001 Frame Trailer Host B Application Presentation Session Transport Network Data Link Physical 2-21
The Application (Upper) Layers Application User interface Examples Telnet, HTTP Presentation How data is presented Special processing, such as encryption Examples FTP enables you to choose binary or ASCII transfer. Session Keeping different applications data separate defines how to start, control, and end conversations (called sessions). Examples Operating system/application access scheduling 2-22
The Data-Flow (Lower) Layers Transport Focuses on issues related to data delivery Reliable or unreliable delivery Segmentation of large application data Error correction before transmit Examples: TCP, UDP, Network This layer defines end-to-end delivery of packets. Provide logical addressing which routers use for path determination Examples: IP, 2-23
The Lower Layers (cont.) Data link These protocols are necessarily concerned with the type of media Combines bits into bytes and bytes into frames Access to media using MAC address Error detection not correction Physical Moves bits between devices Specifies voltage, wire speed, and pinout cable. 2-24
The Data-Flow (Lower) Layers Transport Focuses on issues related to data delivery Reliable or unreliable delivery Segmentation of large application data Error correction before transmi Network This layer defines end-to-end delivery of packets. Provide logical addressing which routers use for path determination 2-25
Network Layer: Path Determination Which Path? Layer 3 functions to find the best path through the internetwork 2-26
Network Layer: Communicate Path 1 2 3 4 5 6 7 8 9 10 11 Addresses represent the path of media connections Routing helps contain broadcasts 2-27
Transport Layer Segments upper-layer applications Establishes an end-to-end connection Sends segments from one end host to another Optionally, ensures data reliability 2-28
Presentation Layer login: Text Data ASCII EBCDIC Encrypted Sound MIDI Video MPEG QuickTime Graphics Visual images PICT TIFF JPEG GIF Provides code formatting and conversion for applications 2-29
Application Layer COMPUTER APPLICATIONS Word Processor Presentation Graphics Spreadsheet Database Design/Manufacturing Project Planning Others NETWORK APPLICATIONS Electronic Mail File Transfer Remote Access Client-Server Process Information Location Network Management Others 2-30
The OSI Model Application Think of browsers. Presentation Think of common data format. Session Think of dialogs and conversations. Transport Think of flow control and reliability. Network Think of path selection, routing, and logical addressing. Data Link Think of frames and media access control. Physical Think of signals and media. 2-31
History and Future of TCP/IP The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions. Some of the layers in the TCP/IP model have the same name as layers in the OSI model. 2-32
TCP/IP model The TCP/IP model has the following four layers Application layer Transport layer Internet layer Network access layer 2-33
Similarities of the OSI and TCP/IP models Both have layers. Both have application layers, though they include very different services. Both have comparable transport and network layers. Networking professionals need to know both models. 2-34
Differences of the OSI and TCP/IP models TCP/IP combines the presentation and session layer into its application layer. TCP/IP combines the OSI data link and physical layers into one layer. IP is called a network layer, or Layer 3, protocol. Similarly, the TCP/IP transport layer defines many functions, including error recovery, as does the OSI transport layer so TCP is called a transport layer, or Layer 4, protocol. 2-35
Thanks Any? 2-36