1. VoIP i2 Architecture Part II
SBC – Southwest Public Safety
VoIP i2 Architecture Part II
9-1-1 Call Routing

2. The Interim VoIP Architecture for Enhanced Services (i2) document was the primary source of information used to create this presentation.
This NENA STANDARD is published by National Emergency Number Association (NENA) as a guide for the designers and manufacturers of systems that are used for the purpose of processing emergency calls.

3. Introduction
VoIP i2 Architecture Part II Call Routing is Part II in the VoIP series.
It is important that you have reviewed Part 1: VoIP i2 Architecture - The IP Domain, prior to viewing this presentation to gain an understanding of the components in the VoIP architecture and the definitions of the acronyms used.
Now here’s a step-by-step look at a 9-1-1VoIP Call Flow

4. 9-1-1 Call Flow Emergency Services VoIP Domain Provider Network
Call Server
2. Call Initiation V1 V4
7. Invite (ESRN,ESQK)
ESGW
8. Call route
(ESQK)
E9-1-1
Selective Router
9. Deliver Call
(ESQK)
PSAP
6. Response
(ESRN, ESQK, LRO) V2
3. Query
(Callback LIE),
VPC
(ESQK)
10. ALI query
13. ALI response
(Callback, LO)
User
Agent
Endpoint
1. LO and/or LK V0
LIS
SRDB
11. ESPOSREQ
Query
12. ESPOSREQ
Response (CBN, LO)
5. Response (LO) V3
4. Query (LK)
VDB
ERDB
DBMS
MSAG
14. ESQK De-allocation

5. Basic Call Routing of a VoIP Emergency Call
GOT IT?
Now the next slide also has the IP Call Flow graphically depicted. But on this slide you can click on any of the indicated steps in the call flow for a closer look at that particular step.

6. 9-1-1 Call Flow Emergency Services VoIP Domain Provider Network
Call Server
2. Call Initiation V4
7. Invite (ESRN,ESQK)
ESGW
E9-1-1
Selective Router
8. Call route
(ESQK)
9. Deliver Call
(ESQK)
PSAP
6. Response
(ESRN, ESQK, LRO) V2
3. Query
(Callback LIE),
VPC V1
SRDB
(ESQK)
10. ALI query
11. ESPOSREQ
Query
User
Agent
Endpoint
13. ALI response
(Callback, LO)
5. Response (LO) V3
4. Query (LK) V0
12. ESPOSREQ
Response (CBN, LO)
1. LO and/or LK
LIS
ERDB
MSAG
14. ESQK De-allocation
MSAG
MSAG
VDB
DBMS

7. Step 1 – LO and/or LK
User Agent
Endpoint
Click on picture to see animation
V0 interface
LIS
LO/LK
The LO/LK is downloaded from the Location Information Server (LIS) to the endpoint by the Dynamic Host Configuration Protocol (DHCP) server, using the V0 interface.
Click on this button to return to the diagram

8. Step 2 – Call Initiation
Call server
User Agent
Endpoint
V1 interface LO
The VoIP endpoint originates an emergency call by sending a call initiation request, designating as the target destination, and including Callback information, and the LO using the V1 interface.

9. Step 3 – Query
Call server
Routing request
VPC
V2 interface
The Call Server receives the call initiation request and sends a routing request to the VPC using the information received in the call request over the V2 interface.

10. Step 4 – Query (LK) Step 5 – Response (LO)
VPC
Location Key
LIS
V3 interface
Location
The VPC queries the identified LIS over the V3 interface, including the received location key.
The LIS returns to the VPC the LO it has associated with the Client-ID.

11. Step 6 – Response
Call server
VPC
V2 interface
Location
(LO)
ESQK/ESRN, LO
ERDB
ESQK/ESRN
The VPC uses the LO to obtain the ESZ-related routing information from the ERDB (including the, ESRN, ESN, and CRN) that will enable the routing via the ESGW to the SR that serves this ESZ.
The VPC uses the received routing information to allocate an available ESQK from the pool of ESQKs appropriate for the SR/ESN associated with the caller’s location/ESZ and sends a response to the routing request for this call, including the allocated ESQK and ESRN, as well as the appropriate LRO.

12. Step 7 – Invite (ESRN, ESQK)
Call
server
ESGW
ESQK/ESRN
V4 interface
The Call Server will take the ESRN received in the response and use it as the basis for selecting the appropriate ESGW with which to route the emergency call.
The Call Server routes the call to the ESGW, including the ESRN provided by the VPC and the ESQK.

13. Step 8 - Call Route
ESGW
E9-1-1 Selective Router
ESQK
CAMA/ SS7
The ESGW uses the received ESRN to select an outgoing route (i.e., trunk group) to the appropriate E9‑1‑1 SR.
The ESGW signals an emergency call origination to the E9‑1‑1 SR, using outgoing (SS7 or MF) signaling that includes the digits “9-1-1” as the called number and the ESQK as the calling number/ANI.

14. Step 9 – Deliver Call
E9-1-1 S/R
PSAP
ESQK
ESQK
SRDB
ESN
The SR receives the emergency call, uses the ESQK to query the SRDB for the associated Emergency Service Number (ESN), and uses the ESN to identify the appropriate PSAP for the call.
The SR then delivers the call to the appropriate PSAP, signaling the ESQK as the Automatic Number Identification (ANI) information.

15. Step 10 – ALI Query
PSAP
ALI
Database
ESQK
The PSAP ANI/ALI controller receives the call setup signaling, and sends an ALI query to its serving ALI DB, using the ESQK as the query key.

16. Step 11 - ESPOSREQ
VPC
ALI
Database
ESPOSREQ
w/ESQK
The ALI DB sends an Emergency Services Positioning Request (ESPOSREQ) to the VPC (identified in the shell record for the ESQK in the ALI DB), which includes the ESQK as the query key in the request.
For further information on ESPOSREQ, click on the acronym

17. ESPOSREQ
Emergency Service Position Request from ALI to MPC, is used to request the initial, updated, or last known position of a wireless handset or other device.
If the requesting entity is authorized, the VPC shall use the ESQK contained in the Emergency Services Routing Key parameter of the ESPOSREQ message to identify the call instance, and to look up the associated call and location-related information stored at the VPC.

18. Step 12 - ALI Query
ALI
Database
VPC
ESPOSREQ
CBN, LOC, VSP
The VPC receives the ESPOSREQ from the ALI DB, and uses the ESQK to retrieve the ALI record information it stored previously (in Step 4).
The VPC returns the ESPOSREQ response to the ALI DB to provide the Callback Number, the Location information, and the VSP provided information that can be supported by the V-E2 interface.

19. Step 13 - ALI Response
ALI
Database
John Smith xxx-xxx-xxxx
1234 W. 6th Ave
Eagle Lake, MO.
Fire - xxx xxx -xxxx
EMS - xxx-xxx -xxxx
Police - xxx- xxx-xxxx
ALI Response
The ALI DB receives the ESPOREQ from the VPC (it may also extract additional information from the shell record for the ESQK).
The ALI DB returns an ALI response to the PSAP, following requirements in NENA

20. Step 14 – ESQK De-allocation
When the VPC receives an indication that a particular instance of an emergency call is being cleared, the VPC de-allocates the associated ESQK and makes it
available for subsequent emergency calls.
Note that release of the ESQK may occur as a result of an indication of call release over the V2 interface from the Call Server/Routing Proxy, or the expiration of the ESQK guard timer, whichever occurs first.

21. One More Time Altogether!
9-1-1 Call Flow
Emergency Services
Provider Network
VoIP Domain
Call Server
2. Call Initiation V1 V4
7. Invite (ESRN,ESQK)
ESGW
8. Call route
(ESQK)
E9-1-1
Selective Router
9. Deliver Call
(ESQK)
PSAP
6. Response
(ESRN, ESQK, LRO) V2
3. Query
(Callback LIE),
VPC
(ESQK)
10. ALI query
13. ALI response
(Callback, LO)
User
Agent
Endpoint
1. LO and/or LK V0
LIS
SRDB
11. ESPOSREQ
Query
12. ESPOSREQ
Response (CBN, LO)
5. Response (LO) V3
4. Query (LK)
VDB
ERDB
DBMS
MSAG
14. ESQK De-allocation
SBC – Southwest Public Safety
Frank Abbenhaus