PICMET 2007 Proceedings, 5-9 August, Portland, Oregon - USA © 2007 PICMET

Enhanced 911 Mechanism for Internet Telephony Service

Sun Ok Park, Mi-Young Huh, Jae Cheon Han, Shin Gak KangElectronics and Telecommunications Research Institute (ETRI), Taejon, Korea

Abstract--Internet users are rapidly increased, and variousservices, which use Internet, are invented. Internet telephonyservice is one of them. As Internet services become an ever moreimportant part of people lives - backed by a marked increase inthe number of Internet population - a flow of value-added Webservices have been introduced to the market. Internet telephonyservice was born as a more economical means than PublicSwitched Telephony Network (PSTN) service in terms of callcharge, but more recently is being hailed as an efficient means tocreate new added-values integrating various Internetmultimedia services such as video phone, multi-party conference,and instant messaging.

After emerging as a star player in the market withinnovative technologies, however, VoIP has recently beenchallenged as the U.S. Federal Communications Commission(FCC) issued an order "requiring all VoIP providers to providetheir customers with emergency call service" in May 2005.Internet telephony users have an expectation to be able toinitiate a request for help in case of an emergency. The problemarises for originating calls made to emergency services, whereVoIP devices move while identifiers remain the same and thecaller's location cannot be provided. So, unfortunately theexisting mechanisms to support emergency calls that haveevolved within the PSTN, are not appropriate to handle evolvingIP-based telephony service.

In this paper, we introduce E911 service and suggest themechanisms that solve the problem of E911 service calling onSIP-based VoIP system.

I. INTRODUCTION

Internet users are rapidly increased, and various services,which use Internet, are invented.

As Internet services become an ever more important partof most people's daily lives - backed by a marked increase inthe number of Internet population - a flow of value-addedWeb services have been introduced to the market. Inparticular, standard technologies for Voice over InternetProtocol (VoIP) have come into the spotlight during the pastfew years.

Internet telephony service, one of the most popularservices using VoIP, was born as a more economical meansthan Public Switched Telephony Network (PSTN) service interms of call charge but more recently is being hailed as anefficient means to create new added-values integratingvarious Internet multimedia services such as video phone,multi-party conference, and instant messaging. Added to that,VoIP plays a significant role as the backbone technology thathelps diverse network technologies leap onto their nextadvanced level ofALL IP network technologies.

After emerging as a star player in the market withinnovative technologies, however, VoIP has recently beenchallenged as the U.S. Federal Communications Commission

(FCC) issued an order "requiring all VoIP providers toprovide their customers with emergency call service" in May2005. 911 service - introduced in 1965 by U.S.communications company AT&T as a home emergencyresponse system - is now used by 99°/O of the country'spopulation and this gave the FCC ample reason for pursuingits May order: Anyone who dials 911 from a VoIP phone hasa reasonable expectation that he or she will be connected toan emergency operator because, after all, they can freelyreceive and place calls over the PSTN as well as on VoIPsystem. Hence the need to ensure this expectation is met.

Other countries than America are also going under theirown, in-depth discussions over including the emergencysystem in their VoIP services with the latter being graduallyseen as the next generation technology to replace the existingPSTN service.

The US FCC have formally imposed emergency servicesaccess requirements on VoIP operators. Meanwhile, a numberof US state regulators have taken steps to ensure emergencyservices access compliance by VoIP operators.

Internet telephony users have an expectation to be able toinitiate a request for help in case of an emergency. Theproblem arises for originating calls made to emergencyservices, where VoIP devices move while identifiers remainthe same and the caller's location cannot be provided. So,unfortunately the existing mechanisms to support emergencycalls that have evolved within the PSTN, are not appropriateto handle evolving IP-based telephony service.

In this paper, we introduce E911 service and suggest themechanisms that solve the problem of E9 11 service calling onSIP-based VoIP system.

The problem with SIP-based VoIP system for E911 is,however, unlike the existing PSTN service, the mobility-ensuring nature of IP makes it difficult to geographicallylocate network users, or callers. So, It difficult to route thecall to the appropriate PSAP. We offer the mechanism tosolve this problem and then we offer the mechanism todisplay the emergency caller's location to the PSAP for helpin dispatching emergency assistance to the correct location.

II. STANDARD SIP TECHNOLOGY

Next to the binary-based H.323 signaling protocol forInternet telephony service developed by theTelecommunication World (ITU-T), a more lightweight text-based protocol was deemed necessary to address the specificneeds of the Internet World. The Session Initiation Protocol(SIP) was introduced in the IETF and has meanwhile gainedmaturity and support.

After the Internet Engineering Task Force (IETF)

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adopted the new SIP standard, countries like China and Japanwho introduced Internet telephony service only recently havefollowed suit and next generation communications networkenvironments such as 3GPP, 3GPP2, and NGN have alsoadopted standard SIP technologies as a core technology formultimedia application services. Moreover there arenumerous ongoing processes for engaging the SIP standard innext generation IP-based multimedia application services. Allthese movements have expedited growth (along with theiractivities and discussions) of SIP-related working groupsunder the IETF and put the groups at the heart of the taskforce.

The SIP is the IETF Standard signaling protocol for VoIPapplications, which is also known as IP telephony. When itcomes to unifying several major communication services SIPhas now become the protocol of choice. Now, most InternetTelephony System developed by SIP.

SIP is an application-layer control protocol that canestablish, modify, and terminate multimedia sessions such asInternet telephony calls.

This section introduces the basic operations of SIP usinga simple example.

INVITE ClientBSDP A

i00tTryinoutbounedProxy

ISO(Ringing) Server

200(0K)SDP B

INVITE ClientBSDP A

100(Trying)

1L80(Ringing)200(0K)SDP B

INVITE ClientBSDP A

180(Ringing)

200(0K)SDP B

ACK

Media Session ]

Figure 1. SIP session setup example

Figure 1 shows a typical example of a SIP messageexchange between two clients, A and B. In this example,Client A uses a SIP application on her PC (referred to as asoftphone) to call Client B on his SIP phone over the Internet.Also shown are two SIP proxy servers that act on behalf ofclient A and B to facilitate the session establishment.

Client A calls Client B using SIP identity called a SIPURI.

In this example, the transaction begins with client A'ssoftphone sending an INVITE request addressed to client B'sSIP URI.

The INVITE request contains a number of header fields.Header fields are named attributes that provide additionalinformation about a message. The ones present in anINVITE include a unique identifier for the call, thedestination address, A's address, and information about thetype of session that clientA wishes to establish with client B.

B's SIP phone receives the INVITE and then B decideswhether to answer the call. B's SIP phone indicates this in a1 80(Ringing) response, which is routed back through the twoproxies in the reverse direction. A's softphone receives the180 (Ringing) response after all.

In this example, B decides to answer the call. When hepicks up the handset, his SIP phone sends a 200 (OK)response to indicate that the call has been answered. The200 (OK) contains a message body with the SDP mediadescription of the type of session that B is willing to establishwith A.

As a result, there is a two-phase exchange of SDPmessages: A sent one to B, and B sent one back to A. Thistwo-phase exchange provides basic negotiation capabilitiesand is based on a simple offer/answer model of SDPexchange.

In the SDP negotiation, A and B have to include samemedia type such as an audio, a video, a text and so on in theSDP. If not, the SDP is not successfully negotiated and themedia session is not set up in two clients.

The SIP-based Internet telephony service guarantees theuser mobility. If SIP user is the place where the Internetconnection is possible, it anytime can use a Internet telephonyservice in a where. So, unfortunately the existing mechanismsto support emergency calls that have evolved within thePSTN, are not appropriate to handle evolving SIP-basedtelephony service.

III. 911 EMERGENCY CALL SERVICE

Back in 2004 in America, a series of failures to connectVoIP callers to 911 services in time to save lives instigatedheated discussions among the public on offering emergencycall service over Internet telephony. This also set alarm bellsringing throughout the world pushing many governmentstowards establishing relevant rules and regulations, serviceproviders towards developing related technologies, andinternational standardization organizations including theIETF towards pursuing standardization of those technologies.

Generally 911 has two types of services: One is Basic911 and the other is Enhanced 911.

Basic 911 Service allows a user to reach a PSAP(PublicSafety Answering Point) serving its current location, but thePSAP may not be able to determine the identity or geographiclocation of the caller (except by having the call taker ask thecaller).

Enhanced 911(E-911) service add the ability to identifythe caller identity and/or caller location to basic 911 services.

The latter, the subject of this paper, not only offersprioritized emergency call connection but also providescallers' location information.

IV. CONSIDERATIONS OF E-911 SERVICE ONINTERNET TELEPHONY SERVICE

The Internet telephony service guarantees the usermobility. If user is the place where the Internet connection is

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possible, it anytime can use a Internet telephony service in awhere. So, unfortunately the existing mechanisms to supportemergency calls that have evolved within the PSTN, are notappropriate to handle evolving IP-based telephony service.

We should consider that how can we get to the locationinformation of emergency caller. When Internet telephonyuser subscribes to the service, we can obtain the initial callerlocation. And then, If Internet telephony user moves, weshould consider another method to obtain the changed userlocation. There are two simple methods. One is direct method.Whenever user moves, calls the service center or access theservice Web site directly. Another is automatic method usingGPS and so on. In case of Vonage ITSP, whenever Vonagecustomer change service location, must update locationinformation. Otherwise, the customer can't support correct E-911 service. In case of Qwest, must call to the special numberor access service Web site.

We also need to consider management of caller locationinformation, method of emergency call routing and locationinformation supporting Mechanism.

I think three solution of emergency call routing.

Selective PSAPRouter

''''_' OME--

mm_g

a\----

1 PSTN

VoIPEnd User W l ----

ESGW(EmergencyService GateWay)

PSAP

EVoIPEnd User

Figure 2. Three mechanism of Emergency call routing

V. E911 SERVICE MECHANISM ON SIP INTERNETTELEPHONY SYSTEM

In this section, We suggest ways to provide E911 serviceon SIP-based VoIP system.

The problem with SIP-based VoIP system for E911 is,however, unlike the existing PSTN service, the mobility-ensuring nature of IP makes it difficult to geographicallylocate network users, or callers. So, It difficult to route thecall to the appropriate PSAP.

We offer the mechanism to solve this problem in sectionA and then we offer the mechanism to display the emergencycaller's location to the PSAP for help in dispatchingemergency assistance to the correct location in section B.

A. Emergency Call Routing MechanismEmergency caller or ECRS(Emergency Call Routing

Support entity) might need to consult a someone to determinethe appropriate PSAP.

We will use REGISTER message to find the appropriatePSAP information.

SIP standard offers a discovery capability. If a userwants to initiate a session with another user, SIP mustdiscover the current host(s) at which the destination user isreachable. This discovery process is frequently accomplishedby SIP network elements such as proxy servers which areresponsible for receiving a request, determining where tosend it based on knowledge of the location of the user, andthen sending it there. To do this, SIP network elementsconsult an abstract service known as a location service, whichprovides address bindings for a particular domain.

SIPClient A(070-330-1456)

REGISTERTo: 0703301456(<-caller number)Contact: 129.254.100.101Body (PIDF-LO)

200(0K)Contact: 129.254.1 00.1 01;

Figure 3. Registrar Behavior for Emergency Call Service

Figure 3 shows registrar behavior for emergency callservice. When Registrar is received REGISTER message toadd binding address, it has to determine the appropriate PSAPfor caller and insert routing information to database. In thistime, Registrar determines the appropriate G/W, routing keyusing caller location information (PIDF-LO).

Routing key information will use to route emergencymessage to selective router(SR) and PSAP.

Routing key describes the location of caller.And then, when Registrar is received REGISTER

message to find binding address, it has to response thebinding address with the routing information stored indatabase to requester. To delivery routing information, wedefine extension URI parameter "gwinfo", "routingkey"

Figure 4 and Figure 5 shows emergency call routingmechanism to support emergency call on SIP Internettelephony system. Figure 4 is Emergency Caller basedsolution. Emergency caller can get the routing informationusing REGISTER message. So emergency caller directly cancall to G/W. In that time, Emergency Caller inserts routingkey to callee number(destination number). So destinationnumber will change from " 119" to "routing key + 119".

Next, figure 5 is ECRS proxy server based solution. In

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this case, ECRS instead of emergency caller has to determinewhere to route the emergency call

REGISTER

200(OK)Contact 129.254.100.101; Registrar

Emcergency gwirm`o=%w#1 " routingkey= 3201

(Client A) SRfl PSAP

INVITE 3201119 (routing key + 119)Froml: 0703301456 (caller number)To:320010)9

Figure 4. Emergency Caller based Call Routing Mechanism

NVlTE ~~REGISTER|INVITE ]

200(0K) To:200(0K)

Emergency 200(OK)

Figure 5. ECRS based Call Routing Mechanism

B. Location Info Supporting MechanismIn this section, We describe mechanism to get the

physical location where emergency calls are received.How is location information provided to the PSAP?PSAP will request caller location information to ALI DB.

If ALI DB has this information, It will response immediately.Otherwise, it will try get caller location information. Thereare many mechanisms.

We suggest the mechanism to provide locationinformation to ALI DB using the REGISTER message. SIPclient register physical location information usingREGISTER to Registrar server. Whenever the client'sphysical location information changes, SIP client reregisterlocation information using REGISTER. And then, WhenPSAP is received emergency call, ALI DB gets locationinformation using the REGISTER, and then ALI DBsubscribe to caller's location information on Registrar usingSUBSCRIBE message. So, Registrar can send notificationswhen those states change.

Figure 6 shows the location information supportingmechanism using REGISTER message.

Enhanced 911 service not only offers prioritizedemergency call connection but also provides callers' locationinformation. the PSAP can identify emergency user's locationinformation using the REGISTER andSUBSCRIBEINOTIFY.

We recommend that emergency caller, Registrar and ALIDB use XML format[4] for carrying geographicalinformation within REGISTER and SUBSCRIBE/NOTIFYmessage. IETF GEOPRIV WG was defined this XML format.This location object extends the PIDF(Presence InformationData Format) [3], which was designed for communicatingprivacy-sensitive presence information and which has similarproperties. Geographical location information describes aphysical position in the world that may correspond to the past,present, or future location of a person, or device.

VI. CONCLUSION

As Internet services become an ever more important partof most people's daily lives - backed by a marked increase inthe number of Internet population - a flow of value-addedWeb services have been introduced to the market. Inparticular, standard technologies for Voice over InternetProtocol (VoIP) have come into the spotlight during the pastfew years.

Today the world is undergoing a massive shift from thetraditional PSTN to All-IP-based Internet telephony, implyingan eventual replacement of the PSTN with VoIP sooner orlater. However FCC's decision to "require VoIP serviceproviders to supply E9 11 capabilities to their customers"imposes legal controls.

Internet Telephony users have an expectation to be ableto initiate a request for help in case of an emergency.Unfortunately, the existing mechanisms to support emergencycalls that have evolved within the PSTN, are not appropriateto handle evolving IP-based telephony service. In this paper,we suggested mechanisms for Emergency calls placed by thepublic using SIP-based VoIP system.

There are still any number of technical issues to betackled and the world will need to put more of its efforts onsolving them.

REFERENCES

1REGISTERr

EmnergencyCaller

(Client A)INVITE 911

20tOKl

[1]cL [2]

[3]

[4]

[5]

[6]

[7]

Eme'46rgeric<yLCall

- RoutDing9Support-

Figure 6. Location Information Supporting Mechanism

J.Rosenberg, et.al., "SIP: Session Initiation Protocol," IETF RFC3261H. Sugano ,et.al, "Presence Information Data Format (PIDF) ," IETFRFC3 863J.Peterson, ,et.al, "A Presence-based GEOPRIV Location ObjectFormat," IETF RFC4119M.Day, et.al., "A Model for Presence and Instant Messaging," IETFRFC2778J.Rosenberg, et.al., "A Presence Event Package for the SessionInitiation Protocol (SIP)," IETF RFC3856A. Niemi, Ed, "Session Initiation Protocol (SIP) Extension for EventState Publication," IETF RFC3903.A. B. Roach, "Session Initiation Protocol (SIP)-Specific EventNotification," IETF RFC3265.

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0.- PSAP

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