Write down the short notes on VTR. Communication between different types of the equipment and software is made possible by making use of the networks. Full-screen text editor is software using which the communication is made possible among the screen and the user. Using editor, text is displayed on screen, cursor can be moved by the user and changes can be done in the text. But, the various rows and columns on the screen are dependent on the terminal which is being used that is the commands to change the cursor  position,  perform  delete  and  insert  operations  on  text  which  varies  as per  the  type  of the terminal. This problem can be ignored by the use of Virtual Terminal Protocol (VTP).

A VTP is the data structure whose information is maintained by the local terminal or application software. This protocol is used to define state of the terminal such as its shape, current position of cursor, number of rows and columns, reverse video indicator and colour. By referencing to this protocol, user and application do their operations irrespective of the terminal-specific issues. For example, the data is displayed on the screen independent of terminal type. VTP protocol does a reverse process when data is entered by the user. This process includes the three steps given below,

(i) The format of data structure is defined by the VTP.

(ii) The user input is converted into the standard form by using the software. 

(iii) The standard screen is read by application.

In case of scrolling, the virtual terminals save more data than the data which can be the displayed on screen, as shown figure below.

 Information stored in the VTI specifies first and last lines of the data displayed window. The displayed data is then defined within the window delimiters. Each time the user scrolls, delimiters are changed by virtual terminal software, thereby retrieving different text lines on the window.