Network Protocols

A protocol is the special set of rules that two or more machines on a network
follow to communicate with each other. They are the standards that allow computers to communicate. A
protocol defines how computers identify one another on a network, the form that the data should take in
transit, and how this information is processed once it reaches its final destination. A protocol is needed
every time we want to perform any task on a network. It may be transferring data or taking a printout on a
network printer or accessing the central database.

Some of the important protocols being used are as follows:

TCP/IP  Transmission Control Protocol / Internet protocol

TCP/IP are the two protocols that are used together and together they form the backbone protocol of the
internet. They can also be used for private networks i.e. intranets and extranets. When you are set up with
direct access to the Internet, your computer is provided with a copy of the TCP/IP program

The Transmission Control Protocol(TCP) breaks the data into packets that the network can handle
efficiently. It manages the assembling of a message or file into smaller packets that are transmitted over the
Internet. It verifies all the packets when they arrive at the destination computer and then reassembles them
in proper order. Data can be lost in the intermediate network. So TCP adds support to detect errors or lost
data and to trigger retransmission until the data is correctly and completely received.
The Internet Protocol(IP)handles the address part of each packet so that it reaches to the right destination.
It gives distinct address (called IP address) to each data packet. Each gateway computer on the network
checks this address to see where to forward the message. Even though some packets from the same
message are routed differently than others, they’ll be reassembled at the destination.
An IP address is a unique identifier for a node or host connection on an IP network. An IP address is a 32 bit
binary number usually represented as 4 decimal values, each representing 8 bits, in the range 0 to 255
(known as octets) separated by decimal points. This is known as “dotted decimal” notation.
Example:
140.179.220.200

The Internet authorities assign ranges of numbers to different organizations. The organizations assign
groups of their numbers to departments. IP operates on gateway machines that move data from
department to organization to region and then around the world.

TCP/IP uses the client/server mode of communication in which a computer user (a client) makes a request
and the server provides the requested service such as sending a Web page.Also TCP/IP communication is
primarily point-to-point transmission of data which means each communication is from one computer in
the network to another computer. TCP/IP and the higher-level applications that use it are collectively said
to be “stateless” because each client request is considered a new request unrelated to any previous one.Till
the time complete message or all packets in a message have been delivered, the connection between the
two computers remains intact but after that the transmission path is available freely. So unlike ordinary
phone conversations that require a dedicated connection for the entire call duration, no dedicated
connection is required. This makes the network paths freely available for everyone to use.

File Transfer protocol (FTP)

This is the simplest and one of the oldest protocols designed for transferring files of any type(ASCII or
binary) from one system to another on the internet. FTP is an application protocol that uses the Internet’s
TCP/IPprotocols.
FTP is based on Client/Server principle. By giving the ftp command with any remote address, the file
transfer can be initiated. In any FTP interface, clients identify the FTP server either by its IP address (such as
192.168.0.1) or by its host name (such as ftp.about.com).

HyperText Transfer Protocol (HTTP)

HTTP is the protocol that is used for transferring hypertext (i.e. text, graphic, image, sound, video etc.)
between two computers and is particularly used on the World Wide Web. It is a TCP/IP based
communication protocol and provides a standard for Web browsers and servers to communicate.

HTTP is based on Client/Server principle. Communication between the host and the client occurs through
a request/response pair. A connection is established between two computers – out of which one is client
(generally the browser)thatinitiates the request and the other is the server that responds to the request.Also
HTTP identifies the resource that the client has requested for and informs the server about the action to be
taken. When the user clicks on the hypertext link, the client program on their computer uses HTTP to
contact the server, identify the resource and ask the server to respond with an action. The server accepts the
request and then uses HTTP to respond to perform the action.

HTTP has three important features. Firstly, it is connectionless.After a request is made, the client
disconnects from the server and waits for a response.To process the request, the server has to re-establish
the connection with the client. Secondly, HTTP is media independent. This means any type of data(text ,
images , sound , video etc.) can be sent by HTTP as long as both the client and server know how to handle
the data content. Thirdly HTTP is stateless.This is because the server and the client are aware of each other
only during a request. Afterwards, they get disconnected.Hence neither the client nor the browser can
retain information between different request across the web pages.

Point to Point Protocol (PPP)

PPP (Point-to-Point Protocol) is usedfor communication between two computers using a serial interface,
mostly a personal computer connected by phone line to a server. For example, an Internet
ServiceProvider(ISP) may provide you with a PPP connection so that the ISP’sserver can respond to your
requests, pass them on to the Internet, and forward your requested Internet responses back to you. It was
basically designed to help communication between two systems through telephone lines as it supports
transmission of network packets over a serial point to point link.

PPP is sometimes considered a member of the TCP/IP suite of protocols. Essentially, it encapsulates and
packages your computer’s TCP/IP packets into PPP frames and then forwards them to the server over
serial transmission lines such as telephone lines, ISDN etc. PPP defines the format of frame to be exchanged
between devices on one or multiple links and also defines the authenticity of the two devices. It supports
various authentication schemes such as Password Authentication Protocol(PAP) and Challenge
Handshake Authentication protocol(CHAP).

E-Mail Protocols

Simple Mail transfer protocol (SMTP)

SMTP stands for Simple Mail Transfer Protocol that allows transmission of email over the Internet. Most
email software is designed to use SMTP for communication purposes when sending email. It only works
for outgoing messages. So when an email has to be sent, the address of their Internet Service Provider’s
SMTP server has to be given. The actual mail transfer is done through Message Transfer Agents(MTA). So
the client computer must have a client MTA and the server must have a server MTA. SMTP actually defines
the MTA client and the server on the internet.

The other purpose of SMTP is to set up communication rules between servers. Every server has its own
way to identify itself, define the mode of communication that they will follow, check for errors and handle
them.In a typical SMTP transaction, a server will identify itself, and announce the kind of operation it is
trying to perform. The other server will authorize the operation, and the message will be sent. If the
recipient address is wrong, or if there is some other problem, the receiving server may reply with some
error message.

Most servers these days actually us a slightly updated version of the SMTP protocol called ESMTP
(Extended Simple Mail Transfer Protocol). This was created to allow transmission of multimedia through
email. When someone sends a picture or music file through their email program, ESMTP communication
codes are used to identify the kind of data being transferred.Mutipurpose Internet Mail Extension(MIME)
is a supplementary protocol that allows non ASCII data to be sent through SMTP. Please note that MIME is
not a protocol and cannot replace SMTP.

Post Office Protocol Version 3 (POP3)

Post Office Protocol 3 or POP3 is the third version of a widespread method of receiving email which
receives and holds email for an individual until they pick it up. SMTP has a disadvantage that if the
destination computer is not online, mails cannot be received.So the SMTP server receives the mail on
behalf of every host and the respective host then interacts with the SMTP server to retrieve messages by
using a client server protocol called POP3.

Remote Access Protocol

Telnet

Telnet is the main internet protocol for creating a connection with a remote machine. It allows you to
connect to remote computers (called remote hosts) over a TCP/IP network (such as the Internet). Once
your telnet client establishes a connection to the remote host, your client becomes a virtual terminal,
allowing you to communicate with the remote host from your computer with whatever privileges you
may have been granted to the specific application and data on that host computer.

Chat Protocol and VOIP

Chatting

A real time informal communication over the Internet is chatting

Internet Relay Chat (IRC)

IRC protocol is used for chatting. It provides chatting between a group or between two individuals. in a group or between two individuals. It was
developed by JarkkoOikarinen in Finland in the late 1980s. It is based on client/server model. The IRC
client sends and receives messages to and from an IRC server. The IRC server transports the message from
one client to another. The IRC server is linked to many other servers to form an IRC network. IRC server
identifies every user through a unique nickname. Each user is assigned a unique channel in case multiple
discussions are taking place.

VOIP

VOIP stands for voice over internet protocol. It enables the transfer of voice using packet switched network
rather than using public switched telephone network. By using VOIP software, phone calls can be done
using standard internet connection. This method of making phone calls is much cheaper than convectional
way because the service of Telecommunication Company is not used.There are three different methods of
VoIP service in common use today

ATA – ATA stands for analog-to-digital converted. It is used to connect the telephone device to the
computer. It takes the analog signals from the phone and converts them to digital signals. These digital
signals can known be transmitted over the internet. Some providers also are bundling ATAs free with their
service.
IP phones – IP phones appear much like an ordinary telephone or cordless phone. They are directly
connected to the router or the LAN. They have all the hardware and software necessary right onboard to
handle the IP call. IP Phones are sometimes called VoIP telephones, SIP phones or Soft phones.

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