Seven Layers of the OSI Model

Physical Layer

Layer 1 Layer 1, provides physical connections for transmission and performs the electrical encoding of data. This layer transforms bits to electrical signals. The lowest, or first, layer of the OSI model. Protocols in the physical layer generate and detect signals so as to transmit and receive data over a network medium. These protocols also set the data transmission rate and monitor data error rates, but do not provide error correction.

Data Link Layer

Layer 2 Switches and bridges operate at this layer Contains information such as the address of the source and destination and the size of the packet; It provides for error checking (Layer 2) Formats data into frames appropriate for transmission onto some physical medium. Defines rules for when the medium can be used. Defines means by which to recognize transmission errors.

Network Layer

Layer 3 The ? Layer provides mechanisms for the routing of data between devices across single or multiple network segments. The third layer of the OSI model. Protocols in the ? layer translate network addresses into their physical counterparts and decide how to route data from the sender to the receiver. Layer 3, responsible for routing, addressing, and fragmentation of data through a communication network. (e.g. routers)

Transport Layer

Layer 4 Layer 4, provides end-to-end transmissions (e.g. UDP, TCP, SMTP) 4th layer; protocols ensure that data are transferred from point A to point B reliably and without errors; services include flow control, acknowledgment, error correction, segmentation, reassembly, and sequencing A layer of the OSI model that ensures reliable data by sequencing packets and reassembling them into their correct order.

Session Layer

Layer 5 The fifth layer in the OSI model. The ? layer establishes and maintains communication between two nodes on the network. It can be considered the "traffic cop" for network communications. This Layer establishes, maintains, and ends the connection between the end points. It is responsible for establishing connections between two devices. This may involve authentication. Allows 2 applications to communicate over a network by opening a session and synchronizing the involved computers, Devices: Gateway, Protocol: Netbios

Presentation Layer

Layer 6 The sixth layer of the OSI model. Protocols in the ? layer translate between the application and the network. Here, data are formatted in a schema that the network can understand, with the format varying according to the type of network used. The ? layer also manages data encryption and decryption, such as the scrambling of system passwords. Serves as a translator. Layer 6 of the OSI Model. The network layer format data to make data viewable by the user through data presentation, data compression and data encryption

Application Layer

Layer 7 Layer 7 of the OSI model. The network layer that houses the applications that allow users to access the network. It contains five categories of services, File services, e-mail services , network printing services, Application services and database services. Client Software