OSI model and TCP stack
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| ISO-OSI Model |
OSI Overview
• ISO = International Organization for Standardization
• OSI = Open Systems Interconnection
• ISO-OSI Reference Model is a layered and abstract
description for computer communication
– Hardware independent
– Hierarchical
• Functionality is divided into seven protocol layers
– Each layer responds services form the superior layer
– Each layer issues services to the subordinate layer
– Each layer is transparent to the other layers
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| osi layers |
Application Layer
• The seventh layer of the OSI model
• Interface for the network applications
• Issues requests to the presentation layer.
• Known protocols:
• DNS, DHCP
• FTP, HTTP
• POP3, IMAP, SMTP
• ...
Presentation layer
• The sixth layer of the OSI model
• Responds to service requests from the application layer
• Issues service requests to the session layer
• Delivery and formatting of informations
– Code transformation
(e.g. from ASCII, EBCDIC to ASN.1)
• Encryption and compression
• These tasks often get fulfilled by the application layer
Session Layer
• The fifth layer of the OSI model
• Responds to service requests from the
presentation layer
• Issues service requests to the transport layer.
• Controls the initialization, the execution and
The completion of the communication
connection
• E.g. HTTP sessions
Transport Layer
• The fourth layer of the OSI model
• Responds to service requests from the
session layer
• Issues service requests to the network layer
• End to end connection
• Error recovery and flow control
• Ensuring complete data transfer
• Port number
• known protocol:
• TCP, UDP
Network Layer
• The third level of the OSI model
• Responds to service requests from the transport
layer
• Issues service requests to the data link layer.
• Finding the way of the data packets
• Flow control, Overload protection and Debug
• IP address
Data Link Layer
• The second layer of the OSI model
• Responds to service requests from the network
layer
• Issues service requests to the physical layer
• Access to the physical net
• Controls the bit transmission
• MAC address
Physical Layer
• The first layer of the OSI model
• Performs services requested by the data link
layer
• Controls the sending and receiving of the
data bits
• Transforms the bits to electric,
electromagnetic and optic signals
• Defines period and clock cycles
OSI Reference Model
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OSI Reference Model |
TCP/IP Model
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TCP/IP Model |
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