VoIP

1
VoIP Voice over Internet Protocol i2 animated
model
2
ESGW
TA
The VSP sends the call to an Emergency Service
GateWay (ESGW) entity, where the ESRN is used to
identify the dedicated 9-1-1 trunk group that
will route the call to the correct 9-1-1 tandem.
When the call is connected to the 9-1-1 trunk the
ESGW transmits 9-1-1 as the called number and
transmits the ESQK as the automatic number
identification (ANI) that is calling 9-1-1.
The PSAP CPE receives the ESQK and uses it to
query the ALI database.
VoIP subscriber dials 9-1-1
SR
The callers Voice over Internet Service Provider
(VSP) detects their customer has dialed 9-1-1 and
sends a query to a VoIP Positioning Center (VPC).
The query message contains the callers
telephone number and registered address.
Database
Data path
The 9-1-1 tandem receives the ESQK as ANI and
uses that number to query the selective routing
database. The SR database recognizes the ESQK
and returns the ESN that identifies the PSAP that
should get the call.
Voice path
SBC ALI Database
The VPC receives the steered query and returns a
dynamic ALI record containing the callers
telephone number and registered address.
VPC
ERDB/VDB
The ALI database service provider recognizes the
ESQK as a special number that should be steered
to the VPC that assigned the ESQK in step 4 above
and sends a query to that VPC.
The ALI database service provider receives the
dynamic ALI record and passes it back to the PSAP
where it is displayed to the call-taker.
The VPC uses the ESN/ESRN combination to
determine which PSAP the call should route to and
assigns a temporary number called the Emergency
Service Query Key (ESQK) to the call. The VPC
then returns the ESRN, ESQK, and Contingency
Routing Number (CRN), if available, to the VSP.
The VPC buffers the callers information and ESQK
relationship in anticipation of receiving a
steered ALI query from the PSAPs ALI database
service provider (see step 10 below). This
relationship should remain fixed until the VPC
receives notification from the ESGW that the call
has terminated.
The VPC sends a query with the callers address
to the Emergency Routing Data Base (ERDB) which
returns the ESN and an Emergency Service Routing
Number (ESRN) to the VPC. The ESRN identifies
which 9-1-1 tandem the call should be routed
through.
i2 VoIP 9-1-1 Call Flow