Lecture 2(b): Protocols of OSI Model

1. Protocols

            Protocol is a same set of rules and regulations for the communication between two different machines on the same layer level.

Example
           
                   Company “A”                                                      Company “B” 

1.      G.M (Application)                                                  G.M (Application)
2.      Secretary (Session)                                                 Secretary (Session)
3.      Peon (Physical)                                                       Peon (Physical)

According to rules, is there possible that the G.M of Company “A” call to the Peon of Company “B” everyday? Definitely No.

2. Header

            When you write HELLO and send, then the data will move to down as Presentation Layer. On this layer the header of presentation layer is attached with the data. On one step down there is another header of session layer is attached with, and so on.   

3. Encapsulation

Example

If there is a patient and you give a white powder (medicine) to eat, that patient will not take because he does not know about that medicine so he refused. (There is No Communication). If he receives that medicine then it is said communication is done.
On the other hand if I put that medicine in a capsule (Encapsulation) and I said eat it, then he will not eat. I write the name of medicine in “French” on capsule then he will not eat because he does not understand “French” language. If I wrote in English i.e. Amoxil then he eat immediately because he knows and understand that language. (There is communication is done).  

For the communication same set of rules and regulations is required. If one machine knows the French then other machine must know that language (Protocol), otherwise communication will not take place. Due to this Protocol (language) forces the patient to take medicine. 

4. Software

Protocols, headers and encapsulation are software.

As you know about Transport Layer, controls the flow of data.
Flow control because of the:

  1. Connection Awaiting
  2. Connection Less
  3. TCP
  4. Connection Oriented
  5. UDP
 Flow Control

Example

The water (Data) is coming from hand pump (Sender) to a glass (Receiver), after a short time the glass will full and then it will be overflow (Wastage of Data). If you want to reserve the wastage of data then you will have to apply a phenomenon is called flow control. There are two possibilities to control the flow of data:

a)      You will stop the working of hand pump (to decrease the speed of sender)
b)      Or you will start the usage of the water (to increase the speed of receiver)

On the Internet the process of Flow Control is automatic. On the back a process is working called “Speed Utilization” which means that equalizes the speed of sender and receiver.

Connection Oriented

Connection Oriented (Reliable)

In this type of communication, an acknowledgment receipt is generated. This is slow but most reliable.

Example

Slow: the machine will not go ahead whenever he does not understand the data.
Reliable: it is 100% sure that if machine receives the information then go ahead, otherwise not.

Connection Oriented: (Unreliable)

In this type of communication, only one time connection confirmation then always data will be sent. This type of communication little bit fast than connection oriented reliable.

           
Connection Less: (Unreliable)

In this communication, an acknowledgment receipt is not generated. It is fast but unreliable.

Example
           
During the construction of building there are some workers are working. The bricks are coming the worker from floor to other worker on ground. Due to non-acknowledgment, bricks kill the worker on ground but bricks (Data) are coming from floor. Due to the absent of ground worker data is lost.

TCP (Transmission Control Protocol)
           
TCP is the example of Connection Oriented.

UDP (User Datagram Protocol):

UDP is the example of Connection Less.

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