The seven layers of the OSI model are the logical layers and are developed by the ISO (international standardization organization). The purpose of these layers is to understand the transmission of the data flow from the source to the destination and to identify the problems during data transmission. The seven layers include Application, Presentation, Session, Transport, Network, Data link and Physical layer. The sequence of the layers names can be remembered by this phrase “All People seems to need data processing”. Following is the general overview of each of the layer. OSI reference model is now being considered as a primary model for the internetworking and inter computing. The seven layers divide the task of data transmission into sub tasks and then complete the data transmission cycle.
Application Layer
Application layer defines the interfaces of the communication and data transfer. Job transfer, network access, error handing and supports user applications. These protocols are operates on the application layer FTP, DNS, SNMP, SMTP, FINGER, TELNET, TFTP and BOOTP.
Presentation Layer
The basic function of the presentation layer is to present the data into the uniform format. It also translates the data from the application to the network format. This layer is responsible for encryption, decryption, protocol conversion and data compression.
Session Layer
Session layer is responsible for establishing a session between two network users and it also manages who can transfer the data first and for how long. The protocols such as NetBIOS, Mail Slots, Names Pipes and RPC work on the session layer.
Transport Layer
Transport layer manages to provide end to end data transmission delivery and it also checks the errors checking and provides guaranteed error free data transmission. These protocols work on the transport layer TCP, SPX, NETBIOS, ATP and NWLINK.
Network Layer
Network layer translates that how data will travel in the network and it also translates the MAC address into the IP address. Router works on the network layer. At source the data is broken into the smaller pieces known as packets and at the destination data is again reassembled to form the original message. These protocols work on the network layer IP, ICMP, ARP, RIP, OSI, IPX and OSPF and the network devices such as router, Brouter, Gateway and ATM also works on the Network layer.
Data Link Layer
Data link layer defines the procedure for data transmission it also detects and corrects the transmission errors. It also manages link control.
Physical Layer
Network cables, LAN cards, hubs and repeaters work on the physical layer. It also provides the interface between network and the network communication devices. It also checks the number of bits transmitted per second.
Hopefully the above mentioned description provides you the basic overview of the seven layers of the OSI model and their functionalities.