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)