28-04-2011, 12:44 PM
[attachment=13008]
OSI MODEL
• An ISO standard covering all aspects of network communications
• Allows different systems to communicate regardless of their underlying architecture or supplier
• Ensures complete transparency between otherwise incompatible systems
• Consists of seven different layers each defining a segment of the process of moving info. across a network
HEADERS & TRAILERS
• Each layer adds its own information to the message it receives from the layer just above it
• On the receive side, layers strip information added on peer layer of transmit side before passing the message to next higher layer
• Added “control data” is placed to the beginning (header) or/and end of a data packet (trailer)
• The whole package is passed to the layer just below it
• Headers are added to the message at layers 6, 5, 4, 3, and 2. A trailer is added only at layer 2
• Examples of header info: checksum, sender/receiver address, service type
PHYSICAL LAYER
• Purpose: Coordinates the functions required to transmit and receive streams of bits, over physical communication medium
Major issues:
• what type of signals & how are bits represented by signals?
• what physical medium & interface to use?
• How bits are synchronized in Tx and Rx?
DATA LINK LAYER
• Purpose: error-free delivery of frames between two systems on the same network (Node-to-Node)
Major issues:
• what information goes into header/trailer & how are stations addressed?
• how are transmission errors detected and corrected?
• how is transmission flow between stations regulated?
• how is access to “shared transmission channel” regulated?
NETWORK LAYER
• Purpose: source to destination delivery of packet , possibly across multiple networks
Major Issues:
• what info goes into header?
how is packet routed from source to destination
OSI MODEL
• An ISO standard covering all aspects of network communications
• Allows different systems to communicate regardless of their underlying architecture or supplier
• Ensures complete transparency between otherwise incompatible systems
• Consists of seven different layers each defining a segment of the process of moving info. across a network
HEADERS & TRAILERS
• Each layer adds its own information to the message it receives from the layer just above it
• On the receive side, layers strip information added on peer layer of transmit side before passing the message to next higher layer
• Added “control data” is placed to the beginning (header) or/and end of a data packet (trailer)
• The whole package is passed to the layer just below it
• Headers are added to the message at layers 6, 5, 4, 3, and 2. A trailer is added only at layer 2
• Examples of header info: checksum, sender/receiver address, service type
PHYSICAL LAYER
• Purpose: Coordinates the functions required to transmit and receive streams of bits, over physical communication medium
Major issues:
• what type of signals & how are bits represented by signals?
• what physical medium & interface to use?
• How bits are synchronized in Tx and Rx?
DATA LINK LAYER
• Purpose: error-free delivery of frames between two systems on the same network (Node-to-Node)
Major issues:
• what information goes into header/trailer & how are stations addressed?
• how are transmission errors detected and corrected?
• how is transmission flow between stations regulated?
• how is access to “shared transmission channel” regulated?
NETWORK LAYER
• Purpose: source to destination delivery of packet , possibly across multiple networks
Major Issues:
• what info goes into header?
how is packet routed from source to destination
