OSI (Open System Interconnection)

OSI (Open System Interconnection)
   Merupakan proses abstrak dari sebuah aliran komunikasi data.Pemrosesan data dari pembuatan, pengecekan, sampai proses pengiriman data.

SEJARAH OSI
   Pada era 70an banyak perusahaan software yang membuat System Network Architecture (SNA/konfigurasi jaringan), yang antara lain IBM, Digital, Sperry, Burough dan sebagainya.Masing masing perusahaan tersebut membuat aturan yang antara satu sama lain berbeda, misalkan IBM mengembangkan SNA produk digital. Tentunya tidak bisa, hal ini disebabkan protokol nya tidak sama. Analoginya, misalkan anda berbicara dengan bahasa jawa, tentunya akan dimengerti juga oleh orang lain yang berbahasa jawa. Masalah ini bisa dieselesaikan jika anda berbicara menggunakan bahasa standar yang tentunya bisa dimengerti lawan bicara anda.
   Sebelum munculnya model OSI, sistem jaringan komputer sangat berpengaruh kepada pemasok(vendor). OSI berupaya membentuk standar umum jaringan komputer untuk menunjang interpetabilitas(baca=stabil) antara pemasok yang berbeda. Tidak adanya suatu protokol yang sama membuat banyak perangkat tidak bisa saling berkomunikasi.
   Masalah utama dalam berkomunikasi antar komputer dari vendor yang berbeda adalah karena mereka menggunakan protocol dan format data yang berbeda.Menghadapi kenyataan ini, kemudian The Internet Standard Organization(ISO) pada sekitar tahun 1980an meluncurkan standar model yang berisi cara kerja serangkaian protokol SNA model ini selanjutnya dinamakan Open System Interconnection(OSI)

OSI 7 LAYER MODEL

The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Easy Way to Remember the OSI 7 Layer Model

All People Seem to Need Data Processing or Please Do Not Throw Sausage Pizza Away

Special thanks to M. Watkins

Application(Layer 7) This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services.

Presentation(Layer 6) This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Session(Layer 5) This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Transport(Layer 4) This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network(Layer 3) This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Data Link(Layer 2) At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Physical(Layer 1) This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects.

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OSI Layer Model for concentrators

Hubs/Repeaters are found in the Physical Layer

Switches /Bridges/Wireless Access Point are found in the Data Link Layer

Multilayer Switch are found in both the Data Link Layer and Network Layer

Routers are found in the Network Layer

Gateway are found in All 7 of the OSI Layers

Brouter are found in both the Data Link and Network Layer

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OSI OSI 7 Layer Model

7. Application Layer - DHCP, DNS, FTP, HTTP, IMAP4, NNTP, POP3, SMTP, SNMP, SSH, TELNET and NTPmore)

6. Presentation layer – SSL, WEP, WPA, Kerberos,

5. Session layer – Logical Ports 21, 22, 23, 80 etc…

4. Transport - TCP, SPX and UDPmore)

3. Network - IPv4, IPV6, IPX, OSPF, ICMP, IGMP and ARPMP

2. Data Link- 802.11 (WLAN), Wi-Fi, WiMAX, ATM, Ethernet, Token Ring, Frame Relay, PPTP, L2TP and ISDN-ore)

1. Physical-Hubs, Repeaters, Cables, Optical Fiber, SONET/SDN,Coaxial Cable, Twisted Pair Cable and Connectors (more)