TCP/IP

Basics of TCP/IP and OSI Model

The Internet

TCP/IP’s design is a result of its historical role as the protocol system for what was to become the Internet. The Internet, like so many other high-tech developments, grew from research originally performed by the United States Department of Defense.

The Local Area Network (LAN)

As the Internet began to emerge around universities and research institutions, another network concept, the local area network (LAN) was also taking form. LANs developed along with the computer industry and were a response to the need for offices to share computer resources.

OSI MODEL

Path representation of OSI model

Application Layer (7th layer) :

This layer communicates with the ‘Network Aware’ applications. For example, the applications like Microsoft Word, this application doesn’t require network communication until you don’t have to share the file. So for these applications, this application layer is not used. But for the applications like, firing up a web browser, there this application comes into picture.

Presentation Layer (6th layer) :

This layer generifies data. Also the encryption of the data is done in this layer. For a communication to take place, there should a fixed presentation of the data so that the receiver also can decrypt the data. So this layer takes care about this issue.

Session Layer (5th layer) :

Session layer is typically used to create or maintain the session.

Transport Layer (4th layer) :

This layer guarantees that the receiver gets the data that was sent by the transmitter. Information is broken into manageable segments. UDP is a unreliable method but is faster and can be used in real time. TCP is a reliable because acknowledgement for every data is sent. This makes it more secure but also makes the method slower and real time is not possible. A port number is attached to IP address and is called “sockets”. This is used when multiple applications are in use and you have to transfer data. This makes mixing the signal a bad possibility.

Network Layer (3rd layer) :

Network layer is also called path determination layer. This layer is used for determining the best path available so that it can decrease the delay time. IP addressing or logical addressing is added. The data is in form of packets.

Data Link Layer (2nd layer) :

Error checking takes place in this layer. Data link layer is responsible for MAC addressing layer also called Hardware layer. Data unit is frames i.e. the data is passed in frames.

Physical Layer (1st layer) :

It defines the characteristics of the hardware needed to carry the data transmission signal. Here actual data transfer happens. This layer deals with all the hardware’s.

Data Transfer from Transmitter to Receiver :

1. Data is obtained from the user and given to the application layer of the transmitter.
2. The top three layers are generally known as the upper layers. We generally don’t consider those layers. So the data directly moves to the Transfer layer.
3. Using TCP, every data is being acknowledged and is divided into segments.
4. The segments after applying network header, is now into a packet form where it is given the IP.
5. Then it moves to the Data Link Layer, and the data link header is applied and now it becomes a frame.
6. This frame when moved to Physical Layer, converts into binary form (0’s and 1’s) and is ready to be transmitted.
7. The binary format from the Physical Layer of the transmitter gets transferred to the Physical Layer of the receiver.
8. In the receiver, the encrypted data is now decrypted.
9. So the header applied in the Data Link Layer of the transmitter is removed in the Data Link Layer of the receiver and moved to the Network Layer.
10. Similarly, the headers applied in the transmitter layers are removed in the respective receiver layers.
11. After removing all the headers, the data is now fully decrypted and moved to the upper part of the receiver, i.e Application Layer of the receiver.

TCP/IP Model:

Comparison with OSI Model

From the figure, it can be seen that the Application Layer, Presentation Layer and Session Layer from OSI Model are combined together in TCP/IP Model. Similarly, the Data Link and Physical Layer of OSI Model is Network Interface Layer in TCP/IP. But the Transport Layer and Network Layer remain as it is in TCP/IP.

The functions of each layer remains the same as that in OSI Model. So, for example, the function of Network Interface in TCP/IP is same as that of Data Link and Physical Layer in OSI Model.

PS (Way to remember the Layers of the OSI Model):

All People Seem To Need Data Processing.

The first letter of each word in the above sentence correspond to the layers in OSI Model.

• Deep Thakker (Tuples)