What is instant messaging (IM )?

What is instant messaging? Im is short for instant messaging.Instant MessagingAccording to the American famous online dictionary of Internet terms netlingo, its definition is as follows: "Instant Messaging (read as a I-M) is short for IM or IMing, it is a technology that enables people to identify online users online and exchange messages with them in real time. Many people call it the coolest online communication method since the invention of email, A typical im works like this: when someone in the friend list (Buddy List) is logged on online at any time and tries to contact you through your computer, the IM system sends a message to remind you, and then you can establish a chat session with him and enter the message text for communication. Im is considered more spontaneous than email and chat rooms, and you can even surf the web together during real-time text conversations ). There are currently a variety of competing IM services, unfortunately there is no standard: that is, the people you want to communicate with must use the same IM system as you do. Another disadvantage is that Im is not designed for security purposes ."

In addition to the definition of netlingo, there are some other definitions. However, netlingo has a great impact on the definition of professional Internet vocabulary, so it is basically based on this definition, at the same time, netlingo is a dictionary updated online. It often modifies the definition of terms based on changes in Internet technology. In this article, the definition of instant messaging is the latest, in the previous definition, the standardization or security issues were not described. Considering these factors, this article will study based on this definition.

The emergence of instant messaging is closely related to the Internet. Technically, Im is fully implemented based on the TCP/IP network protocol family, the TCP/IP protocol family is the technical basis for the implementation of the entire internet, the earliest instant messaging prototype can be traced back to the network chat protocol IRC (Internet Relay Chat) invented by Finnish Jarkko oikarinen in 1988. This protocol only supports text chat, nor does it support the concept of friend lists. After the first IM product ICQ was invented in 1996, the technology and functions of Instant Messaging began to be basically formed, and its working principles began to be understood, however, the protocols used by different manufacturers to implement the principles of instant messaging technology are quite different, and even the world's major IM service operator AOL (American online: American online) there is still no private agreement published for its main instant messaging product, aim (American Instant Messenger. Even so, we can still describe the technical principles of IM from an IM system that provides the most basic services, no matter how many new features of the current product are, it must follow these basic principles and structures.

First, user a enters the user name and password to log on to the Instant Messaging Server. The server reads the user database to verify the user's identity. If both the user name and password are correct, register the IP address of user A, the version number of the IM client software, and the TCP/UDP port number used, and return the logon success mark of user, at this time, user a's status in the IM system is online (online presence ).

Secondly, based on the list of friends (buddy list) that user a stores on the IM server, the server sends the online information of user a to the PC of the instant messaging friends at the same time, the information includes the online status, IP address, and TCP port number used by the IM client, after receiving this message, the instant messaging software on the PC of the instant messaging friend will prompt a small window on the PC Desktop.

Step 3,Instant MessagingThe server sends the user a's friend list and related information stored on the server to his PC. The information includes the online status, IP address, and TCP port used by the IM client) user A's IM client on the PC will display the list of friends and their online status after receiving the information.

Next, if user a wants to chat with his online friend B, he will directly use the IP address and TCP port number of user B sent from the server, send chat information directly to user B's PC. After receiving the IM client software of user B, it is displayed on the screen. Then user B directly replies to user a's PC, in this way, the instant text messages of both parties do not pass through the IM server, but communicate through the network through point-to-point direct communication, which is called peer-to-peer communication ). In a commercial instant messaging system, if point-to-point communication between user a and user B is difficult to establish or slow due to firewall and network speed, the IM server also provides the message transfer service, that is, all the instant messages of user a and user B are sent to the IM server first, and then forwarded to the other party by the server. Early IM systems used UDP protocol for communication between IM clients and Im servers. UDP is an unreliable transmission protocol, while in direct communication between IM clients, use TCP protocol with reliable transmission capability. With the development of user requirements and technical environment, mainstream instant messaging systems tend to adopt TCP protocol between instant messaging clients, instant messaging clients, and instant messaging servers.

　

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[Reprinted from http://www.linkstalk.com/linkstalk_what_im.html]