08-12-2012, 02:59 PM
OSI Model
osi-model.ppt (Size: 785.5 KB / Downloads: 146)
Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions.
The APPLICATION Layer
The top layer of the OSI model
Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing
The PRESENTATION Layer
Manages data-format information for networked communications (the network’s translator)
For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand
This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression
A special software facility called a “redirector” operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource
The SESSION Layer
Enables two networked resources to hold ongoing communications (called a session) across a network
Applications on either end of the session are able to ex hange data for the duration of the session
This layer is:
Responsible for initiating, maintaining and terminating sessions
Responsible for security and access control to session information (via session participant identification)
Responsible for synchronization services, and for checkpoint services
The TRANSPORT Layer
Manages the transmission of data across a network
Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium)
Reassembles chunks into their original sequence at the receiving end
Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors