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TABLE 1.7 OSI Model Layers and Their Respective Functionalities
OSI Layer Important Functions
Application Provides an interface between a host’s communication software and any necessary external
applications.
Evaluates what resources are necessary and the available resources for communication
between two devices.
Synchronizes client/server applications.
Provides error control and data integrity between applications.
Provides system-independent processes to a host.
Presentation Presents data to the Application layer.
Acts as a data format translator.
Handles the structuring of data and negotiating data transfer syntax to Layer 7.
Processes involved include data encryption, decryption, compression, and decompression.
Session Handles dialog control among devices.
Determines the beginning, middle, and end of a session or conversation that occurs
between applications (intermediary).
Transport Manages end-to-end connections and data delivery between two hosts.
Segments and reassembles data.
Provides transparent data transfer by hiding details of the transmission from the upper
layers.
Network Determines best path for packet delivery across the network.
Determines logical addressing, which can identify the destination of a packet or datagram.
Uses data packets (IP, IPX) and route update packets (RIP, EIGRP, and so on).
Uses routed protocols IP, IPX, and AppleTalk DDP.
Devices include routers and Layer 3 switches.
Data Link Ensures reliable data transfer from the Network layer to the Physical layer.
Oversees physical or hardware addressing.
Formats packets into a frame.
Provides error notification.
Devices include bridges and Layer 2 switches.
Physical Moves bits between nodes.
Assists with the activation, maintenance, and deactivation of physical connectivity between
devices.
Devices include hubs and repeaters.
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