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

DETAILED DESCRIPTION A principal objective of the present invention is to provide a method of polling the status of a plurality of remote data transmission equipment locations in a secure manner.
Another objective is to provide a polling method which does not require any changes in the data transmission or communication equipment.
Other objectives and advantages of the invention shall become apparent from the following description of he invention.
This invention provides an efficient and cryptographically secure method of continuously monitoring the status of data security (encryption) equipment and its physical surroundings (such as burglar alarms) when used in multi-point data communications networks.
In this system (FIG.
1), the "drops" in the network send status reports to a centrally located security monitoring device.
Multipoint networks often use polling protocols to maintain line usage discipline.
The encryption device, which is between the DTE and DCE at each remote location, transmits an encrypted status frame immediately prior to the encrypted response of the drop to a poll.
The cipher text of this status message serves as the initialization vector for the encipherment of the data transmitted by the DTE at this drop thereby minimizing additional overhead for alarm status reporting.
At the central location, the encryptor removes this status message from the data stream so that it is not received by the DTE deciphers it and sends it to a central monitoring facility.