Legacy Selective Router Gateways

N E N A D e v e l o p m e n t C o n f e r e n c e | O c t o b e r 2 0 1 4 | O r l a n d o , F l o r i d a

Legacy Selective Router GatewaysTerry ReeseNENA NG9-1-1 Architecture Evolution Subcommittee Chair

Senior Consultant, Ericsson


Legacy Selective Router Gateways

The 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



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



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



An 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



Transition to NG9-1-1 may include support for the interconnection of legacy Selective Routers (SRs) with a NG Emergency Services Network



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



Legacy 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


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 Query

Location Retrieval

SIP

ECRF



The 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



What 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



Routing 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



Routing 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



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



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



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 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)



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


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 Query

Location 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



When 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



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



Call Routing/Delivery to Legacy SRLSRG must map the SIP address of the target

PSAP to a PSAP Directory NumberLSRG uses the PSAP DN to select the

outgoing trunk group to SRThe 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



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 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



Support for Location Delivery to PSAPThe PSAP uses the pANI to query the ALI

systemThe 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



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



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 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



Transfer 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



Transfer 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



Status of LSRG StandardThe 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



Status of LSRG StandardOpen 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)?



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



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Legacy Selective Router Gateways