Emergency services

How do reach help?
  fire@ police@
  911, 112
  sos@any_domain
  emergency user
  learn local access numbers
  tel: URL
How do you find PSAPs
  fixed PSAP
  registration conveys
    never REGISTER
    3GPP is in home network: inserting in forward/backward path
  fire, police
  unknown origin caller
  enum city-state-US
  two-stage: lat-long to 9-digit zip-code 
  DNS
  DHCP
  LDAP
  
How does PSAP know where you are?
Service restrictions?
Network layer priority and preemption?
Crank calls

PSTN
  E.164 assigned

FCC 911 - PBX caller id
3GPP document 22101