Comparing the OSI and TCP/IP Models

The TCP/IP Protocol:
The TCP/IP protocol suite, also referred to as the Internet
Protocol suite, is the set of communications protocols that
Implements the protocol stack on which the Internet and most
Commercial networks run. It is named after the two most
Important protocols in the suite: the Transmission Control
Protocol (TCP) and the Internet Protocol (IP).
The TCP/IP protocol suite—like the OSI reference model—is
Defined as a set of layers. Upper layers are logically closer to the
User and deal with more abstract data, relying on lower layer
Protocols to translate data into forms that are transmitted
Physically over the network.
The TCP/IP protocol is the primary focus of this tutorial.

TCP/IP Model and the OSI Reference Model:
The TCP/IP protocol suite was developed before the OSI
Reference model. As such, it does not directly map to the 7-layer
OSI reference model. The TCP/IP protocol stack has only layers
That can be loosely mapped to the OSI protocol stack, as shown
In the Figure

Application Layer:
The application layer of the TCP/IP model corresponds to the
application layer of the OSI reference model.
Some well known examples of application level entities within the
TCP/IP domain are:
• FTP/Telnet/SSH

Transport Layer:
The transport layer of the TCP/IP model maps fairly closely to the
transport layer of the OSI model. Two commonly used transport
layer entities are TCP and User Datagram Protocol (UDP)

Internet Layer:
The Internet layer of the TCP/IP model maps to the network layer
of the OSI model. Consequently, the Internet layer is sometimes
referred to as the network layer. The primary component of the
Internet layer is the Internet Protocol (IP).Many of the TCP/IP
routing protocols are also classified as part of the Internet layer.

Network Access Layer:

The lowest layer of the TCP/IP protocol stack is the network
Access layer. The network access layer contains two sublayers,
The media access control (MAC) sublayer and the physical
sublayer. The MAC sublayer aligns closely with the data link
Layer of the OSI model, and is sometimes referred to by that
name. The physical sublayer aligns with the physical layer of the
OSI model.
Note: Some references divide the TCP/IP model into
5 layers, with the MAC and physical layers
Occupying the lowest two layers.
Examples of the network access layer that will be discussed in
This tutorial include:
• Ethernet
• Wireless Fidelity (Wi-FI)/WiMAX
• PPP, PPP over Ethernet (PPPoE)
• ATM/Frame Relay.

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