- Ring with adjustable volume and cadence- Hearing aid compatible amplified handset with thumbwheel volume control- Optional RC-4A for secure remote relay control, see DOD 582- SIP compliant- PoE powered (class 1, <4 Watts)- Outbound Proxy, Authentication ID, Peer to Peer, VLAN Tagging- Network downloadable firmware- Cycles to up to three rollover phone numbers on busy or no-answer- Remotely programmable- Extended temperature range (-40?F to 140?F)- Selectable auto-answer feature for monitoring- Diagnostics (for testing remote RC-4A relay)