OSI-Model

PHYSICAL

Layer 1 the Physical layer defines all the electrical and physical specifications for devices. This includes the layout of pins, voltages, and cable specifications. Hubs, repeaters and network adapters are physical-layer devices.

DATA LINK

Layer 2 transmits frames of data from computer to computer on the same network segment. Ensures the reliability of the physical link established at layer 1. Standards define how data frames are recognized and provide the necessary flow control and error handling at the frame set.

NETWORK

Layer 3 establishes, maintains and terminates network connections. This layer routes data packets across network segments, translates logical addresses and names into physical addresses.

TRANSPORT

Layer 4 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.

Sequences data packets, and requests retransmission of missing packets. It also repackages messages for more efficient transmission over the network.

SESSION

Layer 5 opens manages, and closes conversations between two computers. It performs name recognition and the functions such as security, needed to allow two applications to communicate over the network, also provides error handling.

PRESENTATION

Layer 6 is the presentation layer, usually part of an operating system, converts incoming and outgoing data from one presentation format to another. Presentation layer services include data encryption and text compression.

APPLICATION

Layer 7 gives user applications access to network. This layer represents the services that directly support the user applications such as software for file transfers, database access, and E-mail