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6.5.5 OSI ARCHITECTURE (:seven: application layer (INCLUDES (SNA gateways,…
6.5.5 OSI ARCHITECTURE
Open Systems Interconnection (OSI) reference model, was developed by the International Organization for Standardization (ISO) in 1984.
Contains seven layers
Each layer is self-contained and relatively independent of the other layers in terms of its particular function.
objective of the OSI reference model is to provide a protocol suite used to develop data-networking protocols and
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international networking standards and was designed to facilitate communication between hardware and software systems despite differences in underlying architectures.
in the OSI model each layer communicates not only with the layers above and below it in the local stack, but also with the same layer on the remote system
For example, the application layer on the local system appears to be communicating with the application layer on the remote system.
:two: data link layer
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LAYER 2 SWITCH, BRIDGE,WIRELESS, AP, NIC
:three: network layer
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virtual circuit between the transport layer on the
local device and the transport layer on the remote device.
ROUTER , LAYER 3 SWITCH, PACKET FILTERS
:four: transport layer
reliable and transparent transfer of data
between end points, end-to-end error recovery and flow control
transport layer ensures that all of the data sent to it by the session layer are successfully received by the remote system’s transport layer
responsible for acknowledging every data packet received from the remote transport layer, ensuring that an acknowledgement is received from the remote transport layer for every packet sent.
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:five: session layer
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establishes, manages and terminates the connections between the local and remote application layers
All CONVERSATIONS, DATA EXCHANGES and DIALOGUES between the application layers are managed by the session layer.
:six: presentation layer
transforms data to provide a standard interface for the application layer and provides common communication services, such as
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REFORMATTING (e.g., conversion of Extended
Binary-coded for Decimal Interchange Code [EBCDIC] to ASCII code)
The presentation layer converts the outgoing data into a format acceptable by the network standard and then passes the data to the session layer.
the presentation layer converts data received from the session layer into a format acceptable to the application layer.
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:one: physical layer
hardware that transmits and receives the bit stream as electrical, optical or radio signals over an appropriate medium or carrier.
defines the cables, connectors, cards and physical aspects of the hardware required to physically connect a device to the network.
Error correction and detection is not usually implemented in the physical layer, with a few notable exceptions.
Cell phones and digital microwave systems will typically implement some form of error correction code, not only detecting but actually correcting errors
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The actual implementation of the functions defined in each layer is based on protocols developed for each layer
A protocol is an agreed-upon set of rules and procedures to follow when implementing the tasks associated with a given layer of the OSI model.
intent of the OSI model is to provide a standard interface at each layer and to ensure that each layer does not have to be concerned with the details of how the other layers are implemented.
approach supports system-to-system communication (peer-to-peer relationship) where each layer on the sender side provides information to its peer layer on the receiving side
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