The ability to check that an Alarm Transmission Path (ATP) is available for use is determined by "polling" the circuit.
The frequency of polling will provide increasingly granular network availability as the time between polls is decreased. However, the frequency of circuit polling does not determine the speed in which the circuit is deemed un-serviceable. This is known as the Reporting time and is calculated on the number of polls that have been unsuccessful.
There are two methods of polling that can be utilised in order to gain an accurate determination of network availability or failure, both should be used in conjunction with each other.
Interface or Local network polling
The ability for the communications device (SPT) to connect to the local network in readiness for transmission of an active poll. To loose connection with a network interface provides a high probability that a determined disconnection of the SPT from the network is in place.
Examples of Network Interface checking:-
PSTN - Dial tone and 50V present on the line
IP/Ethernet - Layer 1 activity present.
GPRS/GSM - Ability to register on the radio network and obtain a signal from the local serving cell.
Active Polling - The ability for the SPT to transmit and confirm/verify delivery of an active data transmission across the ATP.