The first LAN messenger for Microsoft Windows is Winpopup, a small utility included in Windows 3.11/95/98/Me intended to receive and send short instant text messages. Winpopup uses SMB/NetBIOS protocol.
Windows NT/2000/XP improves upon this with Messenger service, a Windows service for receiving and sending messages compatible to WinPopup. On systems where this service is running, the received messages "pop up" as simple message boxes. Any software compatible with winpopup, like the console utility NET SEND, can send such messages.
By default, Messenger service is off in Windows XP SP2 and blocked by Windows XP's firewall.
Many alternatives for MS winpopup and NET SEND use proprietary TCP/IP protocols.
ObjectivesThe objectives of LAN messenger are as following:
Increase productivity: By design, the system does not allow users to talk to people outside of the LAN. This will decrease the amount of time people spend talking to outsiders on non-work related issues using public messenger systems.
Network security: The program runs inside the company LAN, so only people who are inside the firewall will have access to the system. The system cannot be spammed from the outside. The data does not leave the LAN so it cannot be snooped by outsiders.
Decrease cost: The LAN Messenger System will help the organization to decrease their cost on phone bills and internet bills.
Secured: Common means of communication, such as verbal instructions, phone conversations and e-mail messaging, are far from perfection when it comes to delivering short messages to multiple individuals. Internet-based instant messaging solutions are good but they rely on third-party services which makes the entire system unreliable in question. The best solution shall be a messenger system working in local network. Quick communication: LAN Messenger System allows quick and fast communication among the users of the system in the organization. There no need to make phone calls, send e-mails or fax.
Highly efficient: Traditional ways to spread information throughout an organization are through meetings, memos, newsletters, and the postal system. Using the LAN Messenger System, all these information can be sent via chat
This article from : http://en.wikipedia.org/wiki/LAN_messenger