ECRIT: Emergency Calling Henning Schulzrinne (with Jong Yul Kim, Wonsang Song, Anshuman Rawat, Matthew Mintz-Habib, Amrita Rajagopal and Xiaotao Wu) Dept

ECRIT: Emergency Calling

Henning Schulzrinne(with Jong Yul Kim, Wonsang Song, Anshuman Rawat, Matthew Mintz-

Habib, Amrita Rajagopal and Xiaotao Wu)

Dept. of Computer ScienceColumbia University

SIP 2006 (Paris, February 2006)

Introduction• Emergency calling is a necessary part of consumer

voice service– citizen calls PSAP (public safety answering point)

for assistance• Existing solutions are insufficient

– may deliver call to wrong PSAP• particularly for nomadic and mobile users

– may not deliver location to PSAP– makes it difficult to move call information around

• e.g., call location to first responder– voice only (+ TDD)


VoIP emergency communications

emergency call

dispatch

civic coordination

emergency alert(“inverse 911”)


Components of emergency calling

Contact well-known number or identifier

Route call to location-appropriate

PSAP

Deliver precise location to call taker

to dispatch emergency help

now transition all IP

112911

112911

dial 112, 911urn:service:sos

selectiverouter

VPC DNS

phone number location(ALI lookup)

in-band key location

in-band


What makes VoIP 112/911 hard?

POTS PSTN-emulation VoIP end-to-end VoIP

(landline) phone number limited to limited area

landline phone number anywhere in US (cf. German 180)

no phone number or phone number anywhere around the world

regional carrier national or continent-wide carrier

enterprise “carrier” or anybody with a peer-to-peer device

voice provider = line provider (~ business relationship)

voice provider ≠ ISP voice provider ≠ ISP

national protocols and call routing

probably North America + EU

international protocols and routing

location = line location

mostly residential or small business

stationary, nomadic, wireless


The core problem

Voice Service Provider (VSP)sees emergency call

but does not know caller location

ISP/IAP knows user locationbut does not handle call


Staged deployment• ~6,134 PSAPs in North America

– average 2-3 active call takers each– some serve town, some large parts of a state– only ~30% of PSAPs can receive geo coordinates– 30-40% may be voice only– many using 1970s telecom technology

• “CAMA” (operator) trunks• limited to delivering 8 (regional) or 10 digits (national) of

information• already facing pressure from supporting cellular services

– Phase I (cell tower and face) and Phase II (caller geo location)

• EU: smaller number of PSAPs, but often without location delivery• Initial version (“I1”):

– dial 10-digit administrative number– like telematics services– does not deliver caller location to PSAP


More than pain…• Multimedia from the caller

– video capture from cell phones– video for sign language– text messaging and real-time text for the deaf

• Data delivery– caller data: floor plan, hazmat data, medical alerts– measurement data input: automobile crash data,

EKGs, …• Delivering video to the caller

– e.g., CPR training• Load balancing and redundancy

– currently only limited secondary PSAP– VoIP can transfer overload calls anywhere

• Location delivery– carry location with forwarded and transferred calls– multiple location objects (civic + geo)


Options for location delivery• L2: LLDP-MED (standardized version of

CDP + location data)– periodic per-port broadcast of

configuration information• L3: DHCP for

– geospatial (RFC 3825)– civic (draft-ietf-geopriv-dhcp-civil)

• L7: proposals for retrievals– by IP address– by MAC address– by identifier (conveyed by DHCP or PPP)


IETF ECRIT working group• Emergency Contact Resolution with Internet Technologies• Solve four major pieces of the puzzle:

– location conveyance (with SIPPING & GEOPRIV)– emergency call identification– mapping geo and civic caller locations to PSAP– discovery of local and visited emergency dial string

• Not solving– location discovery– inter-PSAP communication and coordination– citizen notification

• Current status:– finishing general and security requirements– tentative agreement on mapping protocol and identifier– later, to work on overall architecture and UA requirements


Emergency identifier requirements• Direct user interface, without “dialing” number

– but do NOT require user to input this identifier directly

– i.e., separate user interface from protocol identifier!

• Reach emergency help in any country, without knowledge of local numbers– also, universally recognizable by proxies

regardless of location of caller• Deployable incrementally

– even if not all entities support the mechanism• Testable without impacting PSAP (human)

resources


Defining an (emergency) services URN• URN = universal resource name

– identifies resource, not its network location– translated by protocol (e.g., DNS) into location(s)

• New: service URN urn:service:service• Identifies a generic service, not a specific resource• Uses mapping protocol:

– {identifier, location} URL(s)• Can be used anywhere a URN or URL is allowed, e.g.:

– web pages– result returned by mapping protocol– request and To URI in SIP

• For emergency services:– urn:service:sos, urn:service:sos.fire, urn:service:sos.police,

urn:service:sos.marine, urn:service:sos.mountain, urn:service:sos.rescue, urn:service:sos.poison, urn:service:sos.suicide, urn:service:sos.mental-health

• Could also be used for other services: urn:service:directory


UA recognition & UA resolution

INVITE sip:[email protected]: urn:service:sos

<location>

9-1-1(dial string)

mapping


<location>

leonianj.gov

mapping may recurse

location information

DHCPLLDP-MED


UA recognition & proxy resolution

9-1-1

mapping

INVITE urn:service:sosTo: urn:service:sos

<location>


<location>

provider.com


UA recognition & proxy resolution(proxy location determination)

9-1-1

mapping

INVITE urn:service:sosTo: urn:service:sos

INVITE sip:[email protected]: urn:service:sosLocation: <location>

provider.com


Proxy recognition & proxy resolution

9-1-1

mapping

INVITE sip:[email protected];user=phoneTo: sip:[email protected];user=phone

INVITE sip:[email protected]: sip:[email protected];user=phoneLocation: <location>

provider.com


Emergency dial strings• ~60 different dial strings in use

– some countries separate fire/police/…, others don’t

– some are used for other services• PBX, information, prefix, …

• Needs to support both home and visited dial string when traveling

• Home = dial string at home location of traveler– traveler may not know local conventions

• Visited = dial string at visited location– fellow tourist picks up phone– babysitter in ex-pat household

• Configure– via DHCP– via SIP configuration mechanism– via location mapping


LUMP: Mapping service URNs + locations to URLs

• Common problem:– {geo or civic location, service} set of URLs– e.g., {Broadway/NY, “911”} [email protected]– also applies to anything from towing service to pizza delivery

• Need to be able to validate addresses ahead of emergency– does this street address resolve to a PSAP?– can the ambulance find the address?

• Service providers don’t trust each other (fully)– e.g., who gets to include Jerusalem in its map– service may depend which warlord you belong to – can’t wait for UN (or ICANN) to create global emergency

services database• Suggested approach: new distributed mapping protocol

– LUMP: location-to-URL mapping protocol– uses SOAP, but special service URLs


LUMP: overview• Support global-scale resolution of service

identifiers (e.g., service URNs) + locations to other URLs

• Attempts to be reliable and scalable– borrow concepts, but not protocol

limitations, from DNS• Architecture: “Forest of trees with a cloud

above”– avoid root as only deployment alternative

• Uses standard web services building blocks


LUMP: Location-to-URL Mapping

clusterserves VSP2

NYUS

NJUS

Bergen CountyNJ US

123 Broad AveLeoniaBergen CountyNJ US

cluster serving VSP1

replicateroot information

searchreferral

rootnodes

LeoniaNJ US

sip:[email protected]

VSP1


LUMP architecture

T1

(.us)

T2

(.de) T3

(.dk)

G

G

GG

G broadcast (gossip)T1: .us

T2: .de

resolver

seeker313 Westview

Leonia, NJ US

Leonia, NJ sip:[email protected]

tree guide


Caching• Generally, UA caches lookup results

– query: “I’m at (X,Y), what’s my PSAP?”– answer: “Your PSAP is sip:[email protected] as long as you stay

in polygon (X1,Y1; X2, Y2; …); this is valid for 12 hours”• almost no impact of node mobility on query frequency

– same for civic: “as long as you stay on Main Street, your town”• civic only relevant for nomadic users

– actual PSAP coverage area may be larger just an optimization

• Almost always avoids query during emergency call– MAY re-query during call– load distribution via DNS

• given frequency of calls for one resolver, likely to be no DNS caching anyway

• Further optimization: query with timestamp (or etag) of last answer– answer: “still the same, thanks for asking”


Performance notes• US: only about 6 calls/second for whole country

– on average, but may spike during mass casualty events

• Use TCP (or TCP/TLS) for reliability• Expect 1-2 queries/day/client• Typical: >> 100 queries/second/server

– almost all rows will be cached in memory•only about 6,000 rows

– one server 8,640,000 queries– probably N+1 spared– data center cost: $300/month/server

$0.0003/user/month (1Mq/day)


Implementation status• Prototype

implementation at Columbia University:– includes referrals– both geo and civic

coordinates– from draft WSDL

(with minor fixes)• Server

– Axis (Apache) SOAP server

– Postgres SQL geo database

• does polygon intersection

• Client– Java app (web page)– Tcl (for our SIP client)


LUMP geo mapping


LUMP: SOAP request


Conclusion• Opportunity to fundamentally restructure emergency

communications– higher reliability with large-scale disasters– lower cost– richer interaction

• IETF ECRIT working group converging on set of solutions

• To be done:– finalize mapping protocol

• additional transport modes?– configuration of dial strings– overall system architecture

Documents

ECRIT: Emergency Calling Henning Schulzrinne (with Jong Yul Kim, Wonsang Song, Anshuman Rawat, Matthew Mintz-Habib, Amrita Rajagopal and Xiaotao Wu) Dept