A switch sentry device (22) having a digital telephony switch (SCX, 16), a device (24) for processing information, a device (24, 34) for simulating a call from the processing device (24) to the switch (SCX, 16), a device (SCX, 16) responsive to the call simulating device (24, 34) for simulating a primary...http://www.google.com.au/patents/US5579368?utm_source=gb-gplus-sharePatent US5579368 - Device for monitoring a switch
