The diagram below shows the deployment of the Dial-Up NCM with dual tandem switches. In this configuration, each Dial-Up NCM separately provides the convenience, flexibility, and importance of remote call-from-anywhere transfer-switch operation, while the standard NCMs in the typical dual-tandem arrangement provide the basic automatic control-link between the two tandem switches, as well as an optional NCM Alarm Unit serving as the primary or backup transfer-switch, and/or circuit monitor, depending on the PSAP manager's needs.

At Tandem Switch A is a 6-Slot NCM Rack with two standard NCM cards and one Dial-Up NCM card. And at Tandem Switch B is a 6-Slot rack with one NCM card and one (optional) Dial-Up NCM card. At PSAP A is an (optional) NCM Alarm Unit equipped with a standard NCM card and a hand-operated transfer switch.

The first purpose of this NCM configuration is to send a signal that will saturate a scan point at the tandem switch and redirect the 9-1-1 calls to an alternate PSAP. By activating a switch on the NCM Alarm Unit at PSAP A, a signal will be sent via the alternate answer circuit to the standard NCM cards at the tandems to activate the remote make busy feature at both Tandem Switch A and B and redirect 9-1-1 calls to PSAP B. Alternately, the Dial-Up NCM at either tandem switch may be called directly from a normal phone, and the command given to switch the on-board relays connected to the same scan points, in parallel with the alternate answer circuit. In either case, The NCM Alarm Unit will give a visual indication (a green LED will light) that the signal to saturate the scan points at the switches has been received at the tandem.

The second purpose of this NCM configuration is automatic circuit monitoring. The standard NCM located in the Alarm Unit at PSAP A will send a heartbeat to the standard NCM card at tandem switch A. If the heartbeat is not received by the NCM card at tandem A then the NCM card at the tandem and in the PSAP Alarm Unit will give a visual and audible alarm indicating the alternate answer circuit is not functioning. The second standard NCM card at Tandem A will send a heartbeat to the standard NCM card at Tandem B. If the heartbeat is not received by the NCM card at Tandem B then the NCM Cards at Tandem A and B and the Alarm Unit in PSAP A will give a visual and audible alarm indicating the alternate answer circuit is not functioning. (The two Dial-Up NCM cards do not participate in circuit monitoring.)

Both the standard and Dial-Up NCM cards comes with four communication channels, so separating wire-line trunks and wireless trunks can be easily handled with separate transfer switches on the Alarm Unit, or appropriate command prompt responses to the Dial-Up NCM.

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