NENA defines three VoiP and E911 stages for migration

NENA defines three VoiP and E911 stages for migration
I1 - deliver the 911call from VoIP
I2 - deliver via 911 network, with ANI and ALI within limits
I3 - deliver via IP-based E911 systems to IP PSAP

Since all I1 and I2 stages will be different in most countries depending on the existing local infrastructure, IETF WG ecrit will deal only with I3 related issues.