Legacy selective router gateways
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Legacy Selective Router Gateways. Terry Reese NENA 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 infrastructure

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Legacy Selective Router Gateways

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Legacy selective router gateways

Legacy Selective Router Gateways

Terry ReeseNENA NG9-1-1 Architecture Evolution Subcommittee Chair

Senior Consultant, Ericsson


Legacy selective router gateways1

Legacy 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


Legacy selective router gateways2

Legacy 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


Legacy selective router gateways3

Legacy 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


Legacy selective router gateways4

Legacy 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


Legacy selective router gateways5

Legacy 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


Legacy selective router gateways6

Legacy 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


Legacy selective router gateways7

Legacy 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


Legacy selective router gateways8

Legacy Selective Router Gateways

  • Example #1: Originating network served by SR; PSAP served by ESInet

MPC/

GMLC

VPC

SRDB

ESRP

ECRF

ECRF

Legacy

SR

Gateway

ALI

SIP

Legacy SR

Legacy

Originating

Network

i2/VSP

Network

SS7

ALI – Automatic Location IdentificationSIP – Session Initiation Protocol

ECRF – Emergency Call Routing FunctionSR – Selective Router

ESRP – Emergency Services Routing ProxySRDB – Selective Routing Database

GMLC – Gateway Mobile Location CenterSS7 – Signaling System No. 7

MPC – Mobile Positioning CenterVPC – VoIP Positioning Center

PSAP – Public Safety Answering PointVSP VoIP Service Provider

i3 PSAPs

Signal Path

Location Retrieval

Routing Query


Legacy selective router gateways9

Legacy 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 2nd tandem


Legacy selective router gateways10

Legacy 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


Legacy selective router gateways11

Legacy 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 maynot be suitable for routing purposes


Legacy selective router gateways12

Legacy 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


Legacy selective router gateways13

Legacy 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


Legacy selective router gateways14

Legacy 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


Legacy selective router gateways15

Legacy 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)


Legacy selective router gateways16

Legacy 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


Legacy selective router gateways17

Legacy Selective Router Gateways

  • Example #2: Originating network served by ESInet; PSAP served by Legacy SR

CIDB

i3 PSAP

LIS

Location Database

SS7

ESRP

Legacy

PSAP

i3 Compliant

Originating

Network

Signaling

SIP

SIP

Legacy

Network

Gateway

ECRF

ECRF

Legacy

SR

Gateway

Legacy

Originating

Network

E2+/PAM

Interface

ALI Interface

Legacy SR

MPC/

ALI

GMLC

ALI – Automatic Location IdentificationLIS – 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 CenterSR – Selective Router

SS7 – Signaling System No. 7

Signal Path

Location Retrieval

Routing Query


Legacy selective router gateways18

Legacy 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


Legacy selective router gateways19

Legacy 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


Legacy selective router gateways20

Legacy 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 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


Legacy selective router gateways21

Legacy 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


Legacy selective router gateways22

Legacy 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


Legacy selective router gateways23

Legacy 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


Legacy selective router gateways24

Legacy 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 2nd Tandem


Legacy selective router gateways25

Legacy 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


Legacy selective router gateways26

Legacy 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


Legacy selective router gateways27

Legacy 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


Legacy selective router gateways28

Legacy 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)?


Legacy selective router gateways29

Legacy 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


Legacy selective router gateways30

Legacy Selective Router Gateways

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