Locution is primarily controlled over IP - not VoIP or RoIP, but rather serial data sent to individual PC's (at each station). The PC at the station then triggers the alert sequence and plays audio out over the overheads. This is all generated from within the PC. As Jay has mentioned, Locution has numerous layers of redundant backups. When a message is sent to a receiving station, the locution controlled expects an "ACK" reply within a very short period of time. If it does not get that response, it will automatically failover to the next "layer". This would be the 800mhz SZ. Like above, only a brief burst of data (individual page) is send to a specific radio ID (one for each station). The radio recieves the individual alert and activates ancillary equipment within the station, much the same as the PC would. All of this happens almost instantaneously. Because the radio just acts as a "Trigger", voice must come from somewhere else, which is what you hear on the talkgroup. The 400 will continue to remain as a complete failover, as DTMF notification for all stations is still active. As you (likely) hear, PSC can still manually activate the alert boards in each station via the DTMF. For anyone interested, I would watch the OSW's on the CC - Look for 0x03C0 0x0308, followed by 0x0319 0x**** ... the **** (hex) when converted to decimal will give you the radio ID the call alert was sent to
Of course, this will only be true IF a station gets alerted over the 800. With a log of some radio ID's following 0x0319 I would think one could come up with something creative to identify the calls...
Cheers