An agreed-upon format for transmitting data between two devices. The protocol determines the following:
a) The Type Of Error-Checking to be Used.
b) Data Compression Method.
c) How the Sending Device Will Indicate that it has finished sending a message.
d) How the Receiving Device Indicate That It has Received a message.
There are a variety of standard protocols from which programmers can choose,
From a user’s point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers,The protocol can be implemented either in hardware or in software.
Protocols exist at several levels in a telecommunication connection. For example, there are protocols for the data interchange at the hardware device level and protocols for data interchange at the application program level.
One of the earliest protocols to be used regularly is called telnet. The telnet protocol allows a user to access a remote computer. If you have the permission of the owner, you can use your computer as a terminal of another computer.
Open Systems Interconnection (OSI),
In the standard model known as Open Systems Interconnection (OSI), there are one or more protocols at each layer in the telecommunication exchange that both ends of the exchange must recognize and observe. Protocols are often described in an industry or international standard.
TCPIP (Transfer Control Protocol / Internet Protocol)
TCPIP (Transfer Control Protocol / Internet Protocol) is the underlying protocol of the Internet today. It is the protocol that helps to split messages up, helps them find their way to the correct destination, then causes them rejoin at the destination. TCPIP is very important, but you rarely interact with it directly. All the other protocols take advantage of it.
HTTP stands for hypertext transfer protocol. This is the protocol you already know and love. The WWW is based on this protocol. HTTP has some interesting characteristics. It was designed to make the Internet easier to use.
FTP stands for File Transfer Protocol. This protocol is a special protocol which is designed to facilitate copying information between computers through the Internet. Whenever you download a file from the Internet, you are probably using a form of the FTP protocol. Much of the time, FTP happens automatically through Web browsers, but there are special FTP programs as well. These FTP clients look like file management programs (with the directory tree structure and all!) except they also allow you to connect to a remote computer as well, and look at the file structure of that computer.