tocTerminating Telephony Services on the InternetVijay K. Gurbani and Xian-He Sun, Senior Member, IEEEI. I NTRODUCTIONA. MotivationB. Overview of PSTN-Originated Crossover ServicesFig. 1. ICW screen popup.C. Genealogy and Early WorkD. ContributionsFig. 2. Simplified PSTN/IN architecture.II. B ACKGROUND ON S ERVICE E XECUTIONA. Service Execution in the PSTNFig. 3. Simplified SIP network.B. Service Execution in the InternetIII. PSTN-O RIGINATED C ROSSOVER S ERVICE A RCHITECTUREA. Choosing a Protocol1) BICC: ITU-T's BICC [ 31 ] is an adaptation of an existing cir2) H.323: ITU-T's H.323 [ 32 ] is an umbrella protocol for estab3) SIP: SIP was described in Section€II-B, here we simply observB. ArchitectureFig. 4. PSTN-originated crossover services architecture.TABLE I S ET OF V ALUES FOR ${\rm E}_{\rm v}$ R ELATED TO A P HOC. Encapsulating Information ElementsTABLE IIS ET OF V ALUES FOR ${\rm E}_{\rm v}$ R ELATED C ELLULD. Usage ModelFig. 5. Notification of incoming call.IV. E XAMPLESA. Crossover Service: Incoming Call AnnouncementB. Crossover Service: Turning Short Message Service to an InstanFig. 6. SMS and instant messaging.V. T AXONOMY OF PSTN-O RIGINATED C ROSSOVER S ERVICESVI. S ECURITY I SSUES W ITH C ROSSOVER S ERVICESVII. R ELATED W ORKVIII. C ONCLUSIONV. Gurbani, Enabling services through protocol interworking, Ph.A. Brusilovsky, V. Gurbani, E. Gausmann, and A. Jain . A proposaA. Brusilovsky, V. Gurbani, D. Varney, and A. Jain . Need for PSV. Gurbani, PSTN Internet notification BOF (pin), in Proc. 44th I. Faynberg, J. Gato, V. Gurbani, and H.-L. Lu . Toward the defiI. Faynberg, J. Gato, and H.-L. Lu, SPIRITS protocol requirementV. Gurbani, A. Brusilovsky, I. Faynberg, H.-L. Lu, M. Unmehopa, J. Rosenberg, Distributed algorithms and protocols for scalable The GEOPRIV Working Group, http://www.ietf.org/html.charters/geoJ. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. PeteS. Petrack and L. Conroy, The PINT service protocol: extensions C. Gbaguidi, J.-P. Hubaux, G. Pacifici, and A. Tantawi, IntegratC. Gbaguidi, J.-P. Hubaux, G. Pacifici, and G. Tantawi, An archiJ. Rosenberg, P. Mataga, and H. Schulzrinne . An application serI. Faynberg, L. Gabuzda, M. Kaplan, and N. Shah, The IntelligentJ. Dianda, V. Gurbani, and M. Jones, SIP services architecture, V. Gurbani, T.-C. Chiang, and S. Kumar, SIP: a routing protocol,SIP service architecture. White paper, Ubiquity Corp., http://wwH. Sinnreich and A. Johnston, Internet Communications Using SIP G. Camarillo, SIP Demystified . New York: McGraw-Hill, 2001.I. Faynberg, L. Gabuzda, T. Jacobson, and H.-L. Lu, The developmM. Bergeren, B. Bollinger, D. Earl, D. Grossman, B.-W. Ho, and RA. Roach, Session Initiation Protocol (SIP) specific event notifJ. Rosenberg . A presence event package for the Session InitiatiJ. Rosenberg, H. Schulzrinne, C. Huitema, and D. Gurle, Session A. Brusilovsky, E. Dacloush, M. Unmehopa, K. Vemuri, A. Zaki, anD. Moreno . Mobility events management in SPIRITS . Internet DraI. Faynberg, L. Gabuzda, and H.-L. Lu, Converged Network and SerV. Gurbani, J. Voelker, and D. Moreno . Location services in SPISPIRITS, The SPIRITS (Services in the Internet Requesting PSTN SBearer Independent Call Control Protocol, International TelecommPacket-Based Multimedia Communication Systems, International TelJ. Peterson and A. Vemuri, Session Initiation Protocol for TelepM. Danley, D. Mulligan, J. Morris, and J. Peterson, Threat analyH.-L. Lu, Pre-SPIRITS implementation of PSTN-initiated services,A. Brusilovsky, J. Buller, L. Conroy, V. Gurbani, and L. SlutsmaV. Gurbani, A. Brusilovsky, I. Faynberg, H.-L. Lu, X.-H. Sun, anV. Gurbani and X.-H. Sun, Extensions to an Internet signaling prIEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 12, NO. 4, AUGUST 2004 571Terminating Telephony Services on the InternetVijay K. Gurbani and Xian-He Sun, Senior Member, IEEEAbstract—We propose a general purpose service architecture forrealizing services which start in the Public Switched TelephoneNetwork (PSTN) but terminate and execute on the Internet. Wediscuss the needs for such services, our early research efforts inthis direction which lead to prototyping certain benchmark ser-vices, and the current state of work in this area. We demonstratethe feasibility of the architecture by focusing on services which in-volve wireline PSTN as well as the wireless aspects (2 G, 2.5 G) ofthe PSTN. Our methodology is attractive since it keeps each of thedomains (PSTN and Internet) unaware as to where the service isexecuting with respect to which domain actually requested the ser-vice. Individual entities participating in the service do not have anyknowledge that external entities from another domain also con-tributed in the execution and fulfillment of such services. Our ap-proach, as embodied in the service architecture, is to leverage thebest of the Internet protocols (SIP, XML, HTTP) and technologies(instant messaging, presence) to provide a general framework forpersonalized service specification and execution.Index Terms—HTTP, Internet, Public Switched Telephone Net-work (PSTN), services, SIP, wireless, wireline.I. INTRODUCTIONTHERE ARE currently two ubiquitous networks in use: thePublic Switched Telephone Network (PSTN) and the In-ternet. Whereas the former is a specialized network whose mainobjective is to transport voice-based media with low delay anda guaranteed quality of service, the latter is a general-purposenetwork which can transport arbitrary media, including voice,video, and data. Increasingly, these networks are merging [28]and the union of these networks has lead to open research ques-tions on at least two planes: the transport plane (i.e., the pro-tocols and procedures for digitizing and transporting voice aspackets over an inherently best-effort delivery network) and theservice plane (i.e., the protocols and procedures for enablingnew services and accessing existing services between the net-works).The work presented here deals exclusively in the service1plane, and is part of an overall research approach for enablingwhat we call crossover services; i.e., services where the intel-ligence to execute them is distributed in multiple network do-mains. Furthermore, a request to start a crossover service origi-Manuscript received May 20, 2002; revised September 27, 2002, and July16, 2003; approved by IEEE/ACM TRANSACTIONS ON NETWORKING EditorH. Schulzrinne.V. K. Gurbani is with the Illinois Institute of Technology, Chicago,