Multimedia Glossary: O

OSI

Open Systems Interconnection model

Work began in 1977 by the ISO to simplify communication between different computer systems. This work resulted in the OSI which is a model specifying functions on a network. OSI does not specify how the functions are to be performed.

The OSI model consists of seven layers:

Layer	Description
1. Physical layer	the cables: physical network connections such as voltage levels, pin assignments
2. Data Link layer	chunks (packages) date into frames (packets)
3. Network layer	routes data through network
4. Transport layer	sequencing and acknowledgement of transmission
5. Session layer	synchronizes dialogue between network applications
6. Presentation layer	converts data for universal exchange
7. Application layer	access from application to other OSI services

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