OSI Reference Model

OSI Reference Model It is a layered model consisting of seven layers. Layers of OSI Model Application: Provides network access for applications, flow control and error recovery. Use protocols like NCP, SMB, SMTP, FTP, SNMP, Telnet, and AppleTalk. Presentation: Performs protocol conversion, encryption and data compression. Use the protocols like NCP, AFP, and TDI. Session: Allows 2 applications to communicate over a network by opening a session and synchronizing. Protocol used NetBIOS. Transport: Repackages messages into smaller formats, provides error free delivery and error handling functions. Use the protocols like NetBEUI, TCP, SPX, and NWLink. Network: Handles addressing, translates logical addresses and names to physical addresses. Use the protocols like IP, IPX, NetBEUI and device used is Router. Data Link: Packages raw bits into frames and includes a cyclical redundancy check. Consists of the LLC sublayer and the MAC sublayer. MAC sublayer is responsible for appending the MAC address of the next hop to the frame header. LLC sublayer uses Destination Service Access Points and Source Service Access Points to create links for the MAC sublayer. The device like Switch, bridge and brouter works on this layer. Physical: Works with the physical media for transmitting and receiving data bits. Multiplexer and repeater are used at this layer. MAC Address: It’s a 48 bit address for uniquely identifying devices on the network. This is a way of presenting the address a 12 hexadecimal digits format. First 6 digits specify the manufacture.