The ISO Virtual Terminal (VT) service and protocol (VTP) allows a host application to control a terminal with screen and keyboard and similar devices like printers. In addition, VTP also supports the less common application-application and terminal-terminal communication.  

VTP is comparable to Telnet in the TCP/IP suite but more powerful. VTP also includes control of cursor movement, colors, character sets and attributes, access rights, synchronization, multiple pages, facility negotation, etc. This means that the huge number of classic terminal type definitions (e.g. in UNIX termcap or terminfo) are unnecessary at each host in the net, as the VT protocol includes the corresponding commands for one abstract virtual terminal that only have to be converted by the local implementation to the actual terminal control sequences. Consequently, the use of VT means not every host needs to know every type of terminal.

As with most ISO standards that require general consensus amongst participating members, the OSI VT has many optional capabilities, two modes of operation and an almost infinite number of implementation specific options. Profiles may help in reducing the optionality present (e.g., there exists a Telnet profile for VT). But it is doubtful that the OSI VT can completely put an end to the 'm x n' terminal incompatibility problem that exists in a heterogeneous computer network.  

Protocol Structure - ISO VTP: ISO Virtual Terminal (VT) Protocol

The ISO VTP is defined in ISO (www.iso.org ) documents 8650 and 8649.