The data can be sent from one point, or node, on the LAN to any other, but there is no guarantee the data will be useful or even understood when it gets there. That is the task of the software residing on the two computers. In many ways, the LAN acts like an express delivery service. Its job is to deliver the data. The rules as to who does what for whom are called protocols.
Many different protocols exist for data communications, making the problem more difficult.
Different vendors have adopted proprietary approaches based on how they see the market. Trying to tie together different systems begins with an understanding of the various protocols. OSI, the only internationally accepted framework of standards for communication between different systems made by different vendors, is more a model than an actively used protocol, but its approach to organizing the communications process into seven layers is widely embraced. The presentation layer deals with how data is represented by providing encryption, format conversion and compression capability. The applications layer is where specific applications services such as file transfer, mail handling and remote access are performed.