Non-interfering in-band protocol-independent diagnostic scanning in a digital multipoint communication system

Claim 1

In a system for interchanging messages between a remote terminal at a first location and a master terminal at a second location, said messages being encoded by using the Data Encryption Standard, a method of monitoring the status of security devices disposed at said first location by a display device disposed at said second location comprising: sensing the status of said security devices at said first location; generating an initializing vector indicative of said status at said first location; receiving plain text data from said remote terminal at said first location; encoding plain text data in accordance with said initializing vector to generate encoded data without adding any data signals indicative of said status to said plain text encoded data; transmitting the encoded data and said initializing vector from said first to said second location; receiving said encoded data and said initializing vector at said second location; decoding the initialization vector to generate a received security message for said display device; and decoding said encoded data in accordance with said initializing vector to generate received plain text data whereby said plain text data contains no information regarding the status of said security devices.