# Digital Trunk Monitor service definition

The Digital Trunk Monitor (DTM) service is a Natural Access service. Natural Access is a development environment for computer-based telephony applications that provides a standard, hardware-independent programming interface.

A Natural Access service is a group of logically related telephony functions. Each service is contained in a service manager, which is a software wrapper surrounding one or more services. The service manager implements binding functions that enable a service to integrate with Natural Access.

A trunk is a transmission channel between two switching stations. For the purpose of the DTM service, consider a BRI, T1, or E1 line (the aggregate of 2, 24, or 30 channels) a single trunk.

The DTM service enables an application to:

- Monitor for alarms on T1 and E1 trunks

- Retrieve trunk state information on BRI trunks

- Gather performance statistics

- Easily detect digital trunk failures

The DTM service can be used to collect statistics and report error counts. A DTM event is generated when any count changes. The application can synchronously retrieve the current counter values from the DTM service's internal cache.

The DTM service demonstration program trunklog is included with Natural Access.

## Alarms and digital trunks

A T1 trunk enters an alarm state upon the presence of red, yellow, or blue alarms. An E1 trunk enters an alarm state upon receipt of local or remote loss of frame errors or excessive bit errors. When the DTM service is used as an alarm monitor, an event is generated when a digital trunk goes into or out of an alarm state. Since failure monitoring is done in the same processing context as call processing, an application can terminate a call and mark its port as unavailable upon receipt of a trunk failure event.

Multiple trunks can be monitored using a single context. The same trunk can be monitored by multiple contexts (and multiple processes).

Note: The alarm state is not applicable to BRI trunks.