Lecture 2(c):OSI Model Vs TCP/IP Model

TCP/IP suit was created by the Department of Defense to ensure and preserve data integrity.OSI Model is the theoretical model while The practical model used in modern networks is the TCP/IP model.

DoD Model	OSI Model	Protocols Used	Function
Process/ Application	Application	Telnet,      FTP,  LPD, SNMP, TFTP, SMTP, NFS, X Window	Defines protocols for node-to-node application communication and also controls user-interface specifications.
	Presentation
	Session
Host-to-Host	Transport	TCP, UDP	Defines protocols for transmission service, creates reliable end-to-end error free communication, handles packet-sequencing and maintains data integrity.
Internet	Network	ICMP, ARP, IP RARP, EIGRP, IGRP, OSPF	Designates the packet for transmission over network, provides IP addresses to hosts and handles routing of packets among multiple networks.
Network Access	Data link Physical	Ethernet, Fast Ethernet, Token Ring, FDDI,X.25,HDLC	Monitors the data exchange between the host and the network. Oversees hardware addressing and defines protocols for physical transmission of data.

Transport Layer in Depth:

The transport layer is possibly the most important layer for exam study purposes. A lot is going on here, and it is heavily tested. The transport layer's main jobs

1.  It sets up and maintains a session connection between two devices.
2.  It can provide for the reliable or unreliable delivery of data across this connection.
3.  It multiplexes connections, allowing multiple applications to simultaneously send and receive data. When
4.  Implementing a reliable connection, sequence numbers and acknowledgments (ACKs) are used.
5.  Flow control (through the use of windowing or acknowledgements)
6.  Reliable connections (through the use of sequence numbers and Acknowledgement )

A )Segmentation:
The first functionality of the Transport Layer is segmentation the data into small units and these
units are called Segment. The benefits of segmentation of data are
1 Easy to error checking
2 Minimum Scope of errors
3 Increases the speed of correction
4 Easy to carry the data on the medium
5 Sequence number
Another functionality of the Transport Layer is that the Transport Layer ensures the reliable
delivery of the data units (segments) to its destination correctly. It is not concern with the
route it concerns only with the Data Retiability between sender and receiver.

 B ) Assign PORT NUMBERS
For the reliable delivery of the data the Transport Layer assign the Port Number to each data
unit from each application and this port number are written in segment header
For example
Port number 21 then it is for FtP
Port number 8O then it is for httP
Port number 23 then it is for Telnet
when sending side computer type an email and send it on the network this email first of all
comes to the Application Layer and Application Laybr provides it the functionality of moving on
the network and' pass it to ltre presentation Layer and Presentation Layer converts this email
into binary numbers'
On Session Layer the session is established betweer'both sides etc.

C ) FLOW CONTROL
To under stand this Method of Flow Control (Reliable Delivery of data transfer) how Network
Layer process it we discuss the following Two Concepts.
1 Windowing
2 Acknowledgement
Windowing and Acknowledgment are interconnected with each other.
When the Transport layer of sending side computer sends Segments to the receiver after
sending the Segments it waits for the Answer for receiving Confirmation, After receiving
confirmation it send the next Segments,
These numbers of Segments are called Windowing or Window Size and Answer for the receiving
confirmation is called Acknowledgment.

 Lecture 2 is End :-)

Now we will discuss Media in Lecture 3.