Terry Reese NENA NG911 Architecture Evolution Subcommittee Chair Senior Consultant Ericsson Legacy Selective Router Gateways The Selective Router SR E911 tandem is a critical element in todays Emergency Services Network ID: 806861
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Slide1
Legacy Selective Router Gateways
Terry Reese
NENA NG9-1-1 Architecture Evolution Subcommittee Chair
Senior Consultant, Ericsson
Slide2Legacy Selective Router Gateways
The Selective Router (SR
)/E9-1-1
tandem is a critical element in today’s Emergency Services Network
infrastructure
Provides the tandem switching of 9-1-1 calls
Controls delivery of the voice call with ANI to the Public Safety Answering Point (PSAP)
Provides Selective Routing, Speed Calling, Selective Transfer, Fixed Transfer, and certain maintenance functions for each PSAP
Slide3Legacy Selective Router Gateways
On the
incoming/ingress
side, the SR interconnects with wireline end office switches and Mobile Switching Centers (MSCs) via dedicated SS7 or MF trunk
groups
On the
outgoing/egress
side, the SR interconnects with PSAPs via Traditional or Enhanced MF trunk groups
Slide4Legacy Selective Router Gateways
Evolution toward NG9-1-1 has been motivated by:
The need to support VoIP callers and NG PSAPs
The desire for better alignment of the Emergency Services architecture with the overall evolution of telecommunications networks to IP-based architectures
Slide5Legacy Selective Router Gateways
An NG9-1-1 solution has 3 major components:
Originating networks
Emergency Services Networks
PSAPs
Different components will evolve at different times/rates
Gateway systems are needed to facilitate transition to an end-to-end NG9-1-1 solution
Slide6Legacy Selective Router Gateways
Transition to NG9-1-1 may include support for the interconnection of legacy Selective Routers (SRs) with a NG Emergency Services
Network
Slide7Legacy Selective Router Gateways
Consider a transitional scenario where:
Emergency Services Network has evolved to an i3 ESInet on which i3 Functional Elements reside
Originating network continues to interconnect with legacy SRs and/or
PSAPs continue to be served by a legacy SR
Slide8Legacy Selective Router Gateways
Legacy Selective Router Gateway (LSRG) provides gateway functionality between legacy SRs and the i3 ESInet
LSRG may be located
on the
ingress side and/or
the egress
side of
an i3 ESInet
Slide9Legacy Selective Router Gateways
Example #1: Originating network served by SR; PSAP served by ESInet
i3 PSAPs
ESRP
Legacy
Originating
Network
i2/VSP
Network
Legacy SR
SRDB
SS7
ALI
MPC/
GMLC
VPC
Legacy
SR
Gatewa
y
ECRF
ALI – Automatic Location Identification
SIP – Session Initiation Protocol
ECRF – Emergency Call Routing Function
SR –
Selective
Router
ESRP
– Emergency Services Routing
Proxy
SRDB
–
Selective Routing Database
GMLC – Gateway Mobile Location Center SS7 – Signaling System No.
7
MPC – Mobile Positioning Center VPC – VoIP Positioning Center
PSAP – Public Safety Answering Point
VSP VoIP Service Provider
Signal Path
Routing Query
Location Retrieval
SIP
ECRF
Slide10Legacy Selective Router Gateways
The LSRG looks to the legacy SR like another legacy SR
Use tandem-to-tandem routing mechanisms to deliver emergency calls to LSRG
NENA 03-003 - SS7 trunk interface with Selective Routing at the 2
nd
tandem
Slide11Legacy Selective Router Gateways
What does the LSRG do when it receives an emergency call from a legacy SR?
Interworks incoming SS7 signaling to outgoing SIP signaling
Routes the call to the ESInet
Needs to obtain location information that can be used to route the call to/through the ESInet
Supports delivery of display/dispatch location to the PSAP
Slide12Legacy Selective Router Gateways
Routing Location vs. Display/Dispatch Location
The LSRG will query the ALI system to obtain location
ALI may need to query an MPC/GMLC in a wireless network or a VPC in an i2 VSP network to obtain location
Location obtained from the ALI system will be used for
display/dispatch
purposes
Location obtain from an ALI system
may
not
be suitable for
routing
purposes
Slide13Legacy Selective Router Gateways
Routing Location vs. Display/Dispatch Location (cont.)
Routing Location must reflect agreements between PSAPs to take certain types of calls on their behalf
For example, PSAP B may agree to handle wireless calls that originate in PSAP A’s serving area on behalf of PSAP A.
Location returned by the ALI system may not reflect such arrangements
Slide14Legacy Selective Router Gateways
How does the LSRG obtain a Routing Location?
For calls from
fixed
or
nomadic
users, the routing location and the display/dispatch location are the same
Location information returned by the ALI system (possibly after querying a VPC) can be used for both routing and display
Slide15Legacy Selective Router Gateways
How does the LSRG obtain a Routing Location? (cont.)
For calls from
mobile
users, the routing location is obtained based on pre- provisioned mappings of the
ESRK or ESRD to a routing location
that, when used to query the ECRF, will cause the call to be routed
to the
desired primary
PSAP
E.g., a point within the desired primary PSAP’s serving area, or a polygon that describes the serving area of the desired primary PSAP
Slide16Legacy Selective Router Gateways
What does the LSRG do when it receives an emergency call from a legacy SR? (cont.)
The LSRG uses the routing location to query the ECRF for routing info
The LSRG interworks incoming SS7 signaling to outgoing SIP signaling and delivers the call to the i3 ESInet with callback and location information
Location-by-value (typically for fixed or nomadic callers)
Location-by-reference (typically for mobile callers)
Slide17Legacy Selective Router Gateways
What does the LSRG do when it receives an emergency call from a legacy SR? (cont.)
If the location information delivered to the i3 ESInet with the call is location-by-reference:
The LSRG will provide
routing
location in response to location de-reference requests from ESRPs
The LSRG will provide
display/dispatch
location in response to location de-reference requests from i3 PSAPs
Slide18Legacy Selective Router Gateways
Example #2: Originating network served by ESInet; PSAP served by Legacy SR
ALI – Automatic Location Identification
LIS – Location Information Server
CIDB
–
Call Information Database
MPC – Mobile Positioning Center
ECRF – Emergency Call Routing Function
PSAP – Public Safety Answering Point
ESRP – Emergency Services Routing Proxy
SIP – Session Initiation Protocol
GMLC – Gateway Mobile Location
Center SR – Selective Router
SS7 – Signaling System No. 7
Signal Path
Routing Query
Location Retrieval
ALI Interface
ESRP
Legacy
Network
Gateway
i3 PSAP
LIS
E2+/PAM
Interface
SS7
Signaling
Legacy
PSAP
ALI
Legacy
Originating
Network
i3 Compliant
Originating
Network
ECRF
Location Database
MPC/
GMLC
CIDB
ECRF
SIP
SIP
Legacy SR
Legacy
SR
Gatewa
y
Slide19Legacy Selective Router Gateways
When an emergency call arrives at an
LSRG
from an
ESRP in an i3 ESInet, the incoming SIP signaling will contain
Callback information
Location (by-reference or by-value)
The SIP address of the target PSAP
Slide20Legacy Selective Router Gateways
What does the LSRG do when it receives an emergency call from an ESRP in an i3 ESInet?
Routes the call to the legacy SR
Provides information to the SR in a format that it understands (i.e., 10-digit keys)
Interworks incoming SIP signaling to outgoing SS7
signaling
Supports delivery of display/dispatch location to the legacy PSAP
Slide21Legacy Selective Router Gateways
Call Routing/Delivery to Legacy SR
LSRG must map the SIP address of the target PSAP to a PSAP Directory Number
LSRG uses the PSAP DN to select the outgoing trunk group to SR
The LSRG signals the call to the SR as if it were another legacy SR
NENA 03-003 – Direct Routing at 2
nd
Tandem
The LSRG must create a 10-digit location key (pANI) and associate it with received location information; passes the pANI to the legacy SR via SS7 signaling
Slide22Legacy Selective Router Gateways
What does the SR do when it receives an emergency call from an LSRG?
Routes the call to the target PSAP based on the PSAP DN
First queries the SRDB with the pANI provided in incoming signaling to obtain ESN information for potential future use (e.g., for Selective Transfer)
Delivers the pANI to the PSAP with the call
Slide23Legacy Selective Router Gateways
Support for Location Delivery to PSAP
The PSAP uses the pANI to query the ALI system
The ALI system uses the pANI to steer the location query to the LSRG, as if it were an MPC/GMLC (e.g., using an E2 query)
The LSRG returns the location information associated with the pANI in an E2 response
If the location information received by the LSRG from the ESRP was a location-by-reference, it must first de-reference the location-by-reference to get location-by-value
Slide24Legacy Selective Router Gateways
What about the
non-location
information provided in the E2 response (e.g., service provider, class of service)?
The LSRG may obtain Additional Call Data from the body of the received SIP message (if provided), or it may need to query a Call Information Database (CIDB) to obtain it
Slide25Legacy Selective Router Gateways
The LSRG will also play a role in the
transfer
of emergency calls between legacy PSAPs that are served by SRs and PSAPs that are served by ESInets
Transfer from PSAP served by SR to PSAP served by ESInet
Transfer from PSAP served by ESInet to PSAP served by legacy SR
Bridged/transferred calls are not routed based on location
Use NENA 03-003 – Direct Routing/Transfer at 2
nd
Tandem
Slide26Legacy Selective Router Gateways
Transfer from PSAP served by SR to PSAP served by ESInet
SR determines destination PSAP address based on digits dialed by PSAP or internal translations
SR routes call over tandem-to-tandem trunks to LSRG
LSRG queries ALI system using ANI/Calling Number to obtain display/dispatch location
Call is routed via ESRP to destination PSAP based on PSAP address
Call is delivered to the destination PSAP with callback and location information
Slide27Legacy Selective Router Gateways
Transfer from PSAP served by ESInet to PSAP served by legacy SR
Transferred call is routed via a conference bridge in the ESInet to the LSRG based on PSAP address
LSRG receives location and callback information with the transferred call
LSRG caches location and creates a pANI which gets delivered to the destination PSAP via the legacy SR
The PSAP queries the ALI system with the pANI, and the ALI steers the query to the LSRG
The LSRG delivers location and non-location information via the ALI system to the PSAP
Slide28Legacy Selective Router Gateways
Status of LSRG Standard
The NENA i3 Architecture WG is in the process of developing a standard for the LSRG
Last worked on in April 2014; work deferred so that WG can focus on All Committee Review comments on i3 standard
Slide29Legacy Selective Router Gateways
Status of LSRG Standard
Open issues:
Draft LSRG standard currently models the signaling between LSRG and legacy SR after the wireless Wireline Compatibility approach (i.e., call is delivered with pANI only)
Should the standard also allow for arrangements in which both callback number and pANI are delivered by the LSRG to the legacy SR (i.e., wireless NCAS approach)?
Slide30Legacy Selective Router Gateways
Open issues: (cont.)
Draft LSRG standard includes a section for call flows; need contributions to complete this section
Initial
Call, Originating Network on ESInet, Primary PSAP on SR
Initial
Call, Originating Network on SR, Primary PSAP on ESInet
Transfer
, Originating Network on ESInet, Primary PSAP on SR, Secondary PSAP on ESInet
Transfer
, Originating Network on ESInet, Primary PSAP on SR, Secondary PSAP on SR
Transfer
, Originating Network on ESInet, Primary PSAP on ESInet, Secondary PSAP on SR
Transfer
, Originating Network on SR, Primary PSAP on SR, Secondary PSAP on ESInet
Transfer
, Originating Network on SR, Primary PSAP on ESInet, Secondary PSAP on ESInet
Transfer
, Originating Network on SR, Primary PSAP on ESInet, Secondary PSAP on SR
Slide31Legacy Selective Router Gateways
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