OSI Internet Protocol Stack

17 Nov

Each Layer serves the above layer and accrue services from bottom layer. We call this a “service model”. Here data is encapsulated in each step.



Provides network based applications to user


· Some widely used applications are standardized

o E.g.: File transfer, Electronic Mail, World Wide Web, Virtual Terminal, Instant Messaging, Directory Services, Remote file systems

Presentation ( formatting data for transmission)

Provides independence to the application processes from differences in data representation (syntax).


· Translation

· Compression

· Encryption

· In practice not implemented in a separate layer but included elsewhere – e.g. in the applications


Provides the control structure for communication between applications; establishes, manages, and terminates connections (sessions) between cooperating applications.


· Dialog Control (full vs. half duplex)‏

· Token Management

· Synchronization

· Recovery Management

· Not often implemented in real systems


Provides reliable, transparent transfer of data between end points; provides end-to-end error recovery and flow control.


· Connection establishment, management and termination

· Multiplexing and demultiplexing

· Error detection and correction

· Flow Control

· Quality of Service


Deliver packets (datagrams) from sender to the receiver (host-to-host) across a communications network. Provides upper layers with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections.


· Logical Addressing

· Which machine to send the packet to

· Routing

· How to get there

· Datagram encapsulation

· Congestion Control

· Lot of packets in the network core

· Quality of Service

· Guarantee levels of service

Data Link

Provides for the reliable transfer of information across the physical link; sends blocks of data (frames) with the necessary synchronization, error control, and flow control.

Data link layer perform “framing”. Responsible for moving data along a single link between two nodes

Data Link Layer is divided into two sub layers (by IEEE 802 standards)


Logical Link Control (LLC) sub-layer – > Hides differences of various MAC networks from the network layer


Medial Access Control (MAC) sub-layer


· Data framing

· Error Detection and handling

· Flow Control(Match and control speed such that receiver is not overloaded)

· Half/full duplex

· Addressing – hardware level

Types of links:

Point to point, broadcast

Broadcast Links

Multiple access problem – Collision

Multiple access protocols (three types)(rules to prevent collision):

· Channel partitioning protocols (TDM, FDM, CDM)

· Random access protocol (CSMA/CD)

· Taking turns protocol (polling, token passing)


MAC address(=LAN address=Physical address)(Consists of 12 hex numbers. e.g. 4A-23-F5-30-FE-AC)

Address Resolution Protocol (ARP)(determining a network host’s MAC address when only IP address is known)


Accept a raw string of bits and deliver it across a link. Converting signal into digital format

Concepts: encoding, synchronization, error detection and correction


· Encoding and signaling

· Data/Signal transmission and reception

· Topology and physical network design

· Hardware Specifications – operations of cables, connectors, wireless radio transceivers, network interface cards and other hardware devices

Logical Link Control (LLC) sub-layer – > Hides differences of various MAC networks from the network layer


Posted by on November 17, 2010 in Acadamic


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2 responses to “OSI Internet Protocol Stack

  1. Dennis

    May 30, 2011 at 2:51 pm

    i like it. Please guide me more notes on the same….kindly requesting

    • Romesh Malinga Perera

      May 31, 2011 at 10:25 pm

      This is a very common topic that we find in computer networks. So with a easy search you will be able to find lot of details on this. But make sure those details are relevant (about OSI not TCP/IP) and reliable.

      p.s.: TCP/IP is another internet protocol stack which talks more on practical aspects.


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