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Legacy Selective Router GatewaysTerry ReeseNENA NG9-1-1 Architecture Evolution Subcommittee ChairSenior Consultant, Ericsson

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Legacy Selective Router GatewaysThe Selective Router (SR)/E9-1-1

tandem is a critical element in today’s Emergency Services Network infrastructureProvides the tandem switching of 9-1-1 callsControls 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

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Legacy Selective Router GatewaysOn 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

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Legacy Selective Router Gateways

Evolution toward NG9-1-1 has been motivated by: The need to support VoIP callers and

NG PSAPsThe desire for better alignment of the

Emergency Services architecture with the overall evolution of telecommunications networks to IP-based architectures

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Legacy Selective Router GatewaysAn NG9-1-1 solution has 3 major

components: Originating networksEmergency Services NetworksPSAPs

Different components will evolve at different times/rates

Gateway systems are needed to facilitate transition to an end-to-end NG9-1-1 solution

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Legacy Selective Router GatewaysTransition to NG9-1-1 may include

support for the interconnection of legacy Selective Routers (SRs) with a NG Emergency Services Network

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Legacy Selective Router GatewaysConsider 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

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Legacy Selective Router GatewaysLegacy Selective Router Gateway

(LSRG) provides gateway functionality between legacy SRs and the i3 ESInetLSRG may be located on the ingress

side and/or the egress side of an i3 ESInet

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Legacy Selective Router GatewaysExample #1: Originating network served

by SR; PSAP served by ESInet

i3 PSAPs

ESRP

Legacy OriginatingNetwork

i2/VSPNetwork

Legacy SR

SRDB

SS7

ALIMPC/GMLC

VPC

Legacy SRGateway

ECRF

ALI – Automatic Location Identification SIP – Session Initiation ProtocolECRF – Emergency Call Routing Function SR – Selective RouterESRP – Emergency Services Routing Proxy SRDB – Selective Routing DatabaseGMLC – Gateway Mobile Location Center SS7 – Signaling System No. 7MPC – Mobile Positioning Center VPC – VoIP Positioning CenterPSAP – Public Safety Answering Point VSP VoIP Service Provider

Signal Path

Routing QueryLocation Retrieval

SIP

ECRF

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Legacy Selective Router GatewaysThe LSRG looks to the legacy SR like

another legacy SR Use tandem-to-tandem routing

mechanisms to deliver emergency calls to LSRGNENA 03-003 - SS7 trunk interface with

Selective Routing at the 2nd tandem

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Legacy Selective Router GatewaysWhat does the LSRG do when it

receives an emergency call from a legacy SR? Interworks incoming SS7 signaling to

outgoing SIP signalingRoutes 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

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Legacy Selective Router GatewaysRouting Location vs.

Display/Dispatch LocationThe LSRG will query the ALI system to

obtain locationALI 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

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Legacy Selective Router GatewaysRouting Location vs.

Display/Dispatch Location (cont.)Routing Location must reflect

agreements between PSAPs to take certain types of calls on their behalfFor 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

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Legacy Selective Router GatewaysHow 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

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Legacy Selective Router GatewaysHow 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

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Legacy Selective Router GatewaysWhat 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 infoThe 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)

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Legacy Selective Router GatewaysWhat 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

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Legacy Selective Router GatewaysExample #2: Originating network served

by ESInet; PSAP served by Legacy SR

ALI – Automatic Location Identification LIS – Location Information ServerCIDB – Call Information Database MPC – Mobile Positioning CenterECRF – Emergency Call Routing Function PSAP – Public Safety Answering PointESRP – Emergency Services Routing Proxy SIP – Session Initiation ProtocolGMLC – Gateway Mobile Location Center SR – Selective Router

SS7 – Signaling System No. 7

Signal Path

Routing QueryLocation Retrieval

ALI Interface

ESRP

LegacyNetworkGateway

i3 PSAP

LIS

E2+/PAM Interface

SS7Signaling Legacy

PSAP

ALI

Legacy OriginatingNetwork

i3 CompliantOriginatingNetwork

ECRFLocation Database

MPC/GMLC

CIDB

ECRF

SIPSIP

Legacy SR

Legacy SRGateway

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Legacy Selective Router GatewaysWhen an emergency call arrives at

an LSRG from an ESRP in an i3 ESInet, the incoming SIP signaling will contain Callback informationLocation (by-reference or by-value)The SIP address of the target PSAP

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Legacy Selective Router GatewaysWhat 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

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Legacy Selective Router GatewaysCall 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 SRNENA 03-003 – Direct Routing at 2nd 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

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Legacy Selective Router GatewaysWhat does the SR do when it

receives an emergency call from an LSRG? Routes the call to the target PSAP

based on the PSAP DNFirst 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

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Legacy Selective Router GatewaysSupport 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 responseIf 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

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Legacy Selective Router GatewaysWhat 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

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Legacy Selective Router GatewaysThe 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 ESInetsTransfer from PSAP served by SR to PSAP

served by ESInetTransfer from PSAP served by ESInet to PSAP

served by legacy SRBridged/transferred calls are not routed

based on locationUse NENA 03-003 – Direct Routing/Transfer at

2nd Tandem

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Legacy Selective Router GatewaysTransfer from PSAP served by SR to

PSAP served by ESInetSR determines destination PSAP address based

on digits dialed by PSAP or internal translations SR routes call over tandem-to-tandem trunks

to LSRGLSRG queries ALI system using ANI/Calling

Number to obtain display/dispatch locationCall is routed via ESRP to destination PSAP

based on PSAP addressCall is delivered to the destination PSAP with

callback and location information

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Legacy Selective Router GatewaysTransfer from PSAP served by ESInet to

PSAP served by legacy SRTransferred call is routed via a conference bridge

in the ESInet to the LSRG based on PSAP addressLSRG receives location and callback information

with the transferred callLSRG 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

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Legacy Selective Router GatewaysStatus of LSRG Standard

The NENA i3 Architecture WG is in the process of developing a standard for the LSRGLast worked on in April 2014; work

deferred so that WG can focus on All Committee Review comments on i3 standard

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Legacy Selective Router GatewaysStatus 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)?

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Legacy Selective Router GatewaysOpen 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

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Legacy Selective Router Gateways

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