What is the need of the protocol in a computer network ?

A protocol is a set of rules and formats that govern the communication between communicating peers. It allows the peers to agree on a set of valid messages and the meaning of each message. In general, protocol mediate any function that requires cooperation between peers.

     An important role of a protocol is to describe the 'semantics' of a message i.e., the meaning associated with the bit carried in a message. A protocol also specifies the actions taken on receipt of a  message.

    Two or more parties at the same level communicating with each other are called peer entities. Peer entities use a protocol to provide a service to higher-level entity. Each shared function (or service) in a communication network is achieved by an associated protocol. Thus a network that provides many services must define many protocols and some of these protocols are independent of each other, while others are dependent.

Which Protocol is used for sending and receiving mails ?

SMTP(Simple Mail Transfer Protocol) is Used for sending and receiving mails.

simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined by RFC 821 (1982, eventually declared STD 10), and last updated by RFC 5321 (2008) which includes the Extended SMTP (ESMTP) additions, and is the protocol in widespread use today.

Network Communication Protocols

       We Know that the word communication is used to denote the transfer of data from one device to another. One necessary condition for communication between two devices is that they should have same interface. I.e., either the two devices should communicate serially or they should communicate parallel. Similarly the signal levels (Current or Voltage), mode of transmission etc. Should also be same. A protocol is one which defines all these parameters so that a communication system is standardized.

So What Is the definition of Protocol in a communication system ?
A protocol is defined as the set of rules and regulations for the communication between two devices.
Thus a protocol ensures that data transmitted by each device in the communication system is understandable to the second device. Some examples of protocols are RS232 (serial communication), Bluetooth (Wireless communication ) etc.
We know that a computer network is a group of interconnected computers. For communication between computers also there should exist a protocol.
Depending on our application various types of protocols are used in computer networks.

1.File Transfer Protocols( FTP)
    As the name implies FTP is protocol used for transferring files between computers connected to local network or internet. Basically FTP is a client/server protocol in which a system running the FTP server accepts commands from a computer running FTP client. FTP server and FTP client are programs that run on two computers. Receiving files from FTP server is called downloading and sending files to FTP server is called uploading.
Various commands are used for these purposes. File transfer protocol contains the procedure for connection establishment between FTP client and FTP server and defines the commands to be used for different purposes.

DEFINITION :
FTP is a protocol that helps to transfer files and information form one computer to another in a local network or internet.


2.Hyper Text Transfer Protocol (HTTP)
HTTP stands for Hyper Text Transfer Protocol. HTTP is also client/server protocol for world wide web (WWW). The client side programs is called web browser and server side program is called web server. HTTP provides a way for a web browser to access the web server and request hyper media documents created using HTML ( Hyper Text Mark Language). As we know HTML documents can contain hyper links to other web sites or web pages.
DEFINITION:
HTTP is a protocol for WWW which enables web browser to access web server and request HTML documents.

3.Transmission Control Protocol/Internet protocol (TCP/IP)
     Basically TCP/IP is a communication protocol designed to interconnect two devices for data or information exchange. It can be computers or other devices. TCP/IP protocol was originally developed by Advanced research projects Agency (ARPA). This protocol was later adapted for the communication in computer networks.

DEFINITION:
TCP/IP is a communication protocol designed to interconnect two devices for data or information exchange.

    TCP/IP contains two protocols. 

1. TCP -transmission control protocol ,

 2.IP -internet protocol

In short TCP/IP is a connection oriented communication protocol where TCP handles flow control and error free packet delivery and IP provides basic addressing and data packets forwarding services.