72
`
`The Internet Telephony Red Herring
`
`Colin Low
`
`Hewlett Packard Laboratories,
`Filton Road, Bristol BS12 6QZ, UK
`cal@ hplb.hpl.hp.com
`
`Abstract
`The spectre of low-cost, real-time voice communication over the
`Internet has polarised Internet service providers and telephone
`network operators, at the expense of finding solutions to the prob(cid:173)
`lem of integrating communications services (in particular, exist(cid:173)
`ing wireless and wireline telephony) with WWW content
`services. This paper argues that solutions not only exist and
`appear to be commercially viable, but could bring about a trans(cid:173)
`formation of the WWW as a tool for business and personal com(cid:173)
`munications.
`
`1.0
`
`Introduction
`
`wireless and wireline telephony with the WWW by using tech(cid:173)
`nology which has existed for some time in the PSTN.
`The technology described within provides:
`• integration of telephony services with WWW content provi(cid:173)
`sion.
`• open telephony service development on the WWW.
`• a devolved service architecture, where services are developed
`by users or any third party developer.
`• evolutionary "market driven" development of services which
`parallels the Darwinian evolution of content services on the
`www.
`• integration with traditional telephony services as exemplified
`in Intelligent Networking by telephony service providers.
`The paper begins by reviewing progress in computer-telephony
`integration which has taken place in the. PSTN over the past two
`decades, under the guise of Intelligent Networking (IN) [1] [3]
`[4] and (in the US) Advanced Intelligent Networks (AIN) [2]. It
`goes on to discuss parallel developments in both the Telecoms
`and the Internet communities which lead in the direction of inte(cid:173)
`grated personal communications, and concludes that there is a
`great deal of value in both approaches. I show that there is a
`hybrid between the two approaches which provides a powerful
`integration between WWW content and existing telephony ser(cid:173)
`vices. Lastly, I outline a prototype constructed by the Nexus
`' project in HP Laboratories which provides a working demonstra(cid:173)
`tion of this approach.
`
`A red herring is an issue which appears to be important and dis(cid:173)
`tracts a discussion or debate away from a topic. It derives from
`the practice of using a strong-smelling smoked herring (or kip(cid:173)
`per) to distract hounds from their prey.
`There are approximately 600 million wireline telephones in the
`world. The increase in the number of new mobile telephony sub(cid:173)
`scribers alone in the past few years has matched the rate of
`growth of Internet users, and in gross numbers and social impact
`is an equally significant phenomenon - the number of mobile sub(cid:173)
`scribers has reached 50 million and is expected to reach 100-150
`million by the year 2000.
`When the Internet and telephones are discussed together it is gen(cid:173)
`erally in the context of Internet Telephony, the use of the Internet
`as a bearer channel for digitised voice communications. Internet
`telephony is an important and exciting new technology which
`will drive many new applications and services, but the commer(cid:173)
`cial value of calls placed on this medium will be insignificant for
`years to come by comparison with current call and service reve(cid:173)
`It is not a secret that the Telecoms industry plans to replace the
`nues generated by conventional telephony. In addition, Internet
`Internet and the WWW with a higher quality, integrated service,
`Telephony runs counter to consumer trends in telephony, which
`favour lightweight, pocket-sized, highly portable handsets which rc multi-media network which offers all the things (it is claimed)
`can be used from anywhere. In this context the debate generated
`the Internet does not - multi-media communication services,
`by Internet Telephony is a red herring because it begs the ques-
`managed bandwidth, quality of service guarantees, security, man-
`ti on 'what do we do with the other 700 million telephones'.
`agement, reliability, and a sensible tariff structure. An example of
`The issue addressed in this paper is the integration of communi-
`a developing architecture can be found in the work of the TINA-
`cation services with WWW information content services. In par-
`C consortium [5].
`ticular,
`it addresses
`the problem of integrating
`the vast Whether these plans are based on misconceptions about the Inter-
`infrastructure of public telephony, normally referred to as the
`net, and whether these plans will reach fulfillment, will be
`Public Switched Telephone Network (PSTN) with the WWW.
`touched upon only in passing, as it is not my intention to take
`The growth in WWW sites as personal or organisational points-
`sides in the polemic between the Internet and Telecoms commu-
`of-contact shows there is a strong demand for integrated commu-
`nities. These plans existed before the Internet explosion, and they
`nications, and this is mirrored by parallel developments in the
`continue to develop in detail. A key technology in these plans is
`telephone industry, which sees itself as the source of communica-
`Intelligent Networking (IN).
`tion services. This paper shows that it is possible to integrate
`
`2.0 Telephony Services -
`Intelligent Networking
`
`0-7803-3336-5/96 $5.00 © 1996 IEEE
`
`Bright House Networks - Ex. 1026, Page 1
`
`

`
`IN emerged in rudimentary form in the '70s. Important develop(cid:173)
`ments were the introduction in the telephone network of stored(cid:173)
`program control switches as a replacement for the older electro(cid:173)
`mechanical switches, and the deployment of out-of-band signal(cid:173)
`ling in the trunk network as a replacement for the practice of
`using the voice bearer channel for signalling. The separation of
`voice bearer channel from signalling was an important develop(cid:173)
`ment, and the signalling function is now implemented by the
`Common Channel Signalling System #7 (SS7) [9]. The separa(cid:173)
`tion of signalling from bearer channel allocation can be seen in
`its most complete form in ISDN [11], where digital end-to-end
`signalling is provided between user terminals, and no relic of in(cid:173)
`band signalling (e.g. DTMF tones) remains.
`The emergence of stored program control switches in the net(cid:173)
`work made it possible to add additional services to switches. The
`best known IN services are 800 number services (Freephone),
`credit-card calling, virtual private networks, and a wide variety of
`personal call handling and redirection services (screening, fol(cid:173)
`low-me, call forwarding, personal numbers etc.). The problem
`with adding services to switches is the complexity of switch soft(cid:173)
`ware, the large code base (e.g. 25 million lines of code), the need
`to avoid compromising extremely high levels of reliability, and in
`consequence, extremely long development and deployment
`times.
`The alternative was to provide an open interface in switches
`which could be used by external service logic to control call han(cid:173)
`dling, and it is this architecture for the provision of telephony ser(cid:173)
`vices outside of the switching or bearer network which is called
`Intelligent Networking. The main focus for IN standardisation is
`the ITU-T, and the Capability Set standards (CS-1, CS-2, CS-3)
`[12] are probably the best reference, but there is significant
`regional involvement via Europe's ETSI, the United States ANSI
`and Japan's TTC.
`The principal functional cmpponents in the IN Distributed Func(cid:173)
`tional Plane are shown in Figure 1.. The Service Switching Point
`(SSP) provides an abstraction of switch and call control
`resources. The Service Control Function (SCF) executes service
`logic external to the switch which assumes call control, making
`use of service, subscriber and subscription data maintained in the
`Service Data Function (SDF). Interaction with the subscriber, via
`DTMF digit collection, recorded announcements, speech record(cid:173)
`ing, and voice recognition takes place via the Special Resource
`Function (SRF) (sometimes called an Intelligent Peripheral). Ser(cid:173)
`vices are created using the Service Creation Function (SCF), and
`the remote management of service installation, subscriber data
`and SSP configuration is carried out using a Service Management
`Function (SMF). The SCF and SDF are normally co-located, and
`the resultant system is called a Service Control Point (SCP).
`The most mature and widely supported part of IN is the SCF-SSP
`interface. Call progression within an SSP is represented by a
`Basic Call State Model (BCSM) (see ITU-T Q.1200 series stan(cid:173)
`dards [12]) which takes two forms, one for the originating portion
`of a call, and the other for the terminating portion. The BSCM
`contains Detection Points (DP) and call states designated Points(cid:173)
`in-Call (PIC). The Service Management Function is used to
`install triggers at detection points, so that when a call passes
`
`73
`
`Bearer Channel
`... ,.. ____ ..,~ SS7 Signalling
`
`Service
`Data
`Function
`
`Specialised
`Resource
`Function
`
`Figure 1. Intelligent Networking
`
`through a trigger, call processing is suspended and interaction
`with the Service Control Function takes place, which can then
`take over many aspects of subsequent call processing.
`Interactions between IN components are implemented using mes(cid:173)
`saging over the SS7 network using the Transaction Capabilities
`Application Part (TCAP) [9], a variant of ISO ROSE, which pro(cid:173)
`vides a symmetric interaction protocol between two peer entities.
`The inter-component message specification is called the IN
`Application Protocol (INAP).
`IN services are often very simple from a conceptual point of view
`- for example, in an 800 number service, the SSP traps the call to
`an 800 number, the SCF uses service logic to determine where to
`route the call (typically based on time-of-day, geographic factors
`and other customer data stored in the SDF) and the SCF instructs
`the SSP to dial the new number, billing the called party. Much of
`the complexity derives from the need to integrate new IN services
`with legacy billing, customer care, and management systems.
`The significance of IN is that there already exists a well-devel(cid:173)
`oped infrastructure within the PSTN for computerised control of
`telephone calls. The importance of intelligence in the PSTN is
`increasing dramatically with the popularity of mobile telephones
`- mobile standards such as GSM are strongly based on ideas
`developed in the IN community (e.g. see [6] [7]). Telephony ser(cid:173)
`vices are popular with subscribers, and there is now a demand for
`increasing levels of integration between wireless and wireline
`telephony, for complex personal number and mobility services,
`
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`
`

`
`74
`
`for enterprise virtual networks, for call distribution services, for
`multimedia content services, for video dial-tone and so on.
`A problem with IN in practice is that telephony services are still
`deployed in the same manner as computing services in the days
`of the corporate mainframe, where applications were hand(cid:173)
`crafted and operated by a large MIS department. Service Control
`Points are typically deployed on a national basis, carry a few ser(cid:173)
`vices, and serve many tens of thousands of subscribers (see [13]
`for a typical deployment).
`
`3.0 Content Services - the WWW
`
`The World Wide Web (WWW) is the exemplar of a global net(cid:173)
`work providing complex content services. It is open, in that any(cid:173)
`one can connect to it and offer content services without asking
`permission. Internet protocols such as TCPIIP and WWW proto(cid:173)
`cols such as HTTP and HTML are global de-facto standards and
`even public domain implementations, available at no cost, are of
`very usable quality. The WWW is highly scalable. Levels of per(cid:173)
`formance in the public network are variable and sometimes
`unsatisfactory Gust like the public road network), but when the
`same technology is deployed in a well resourced private or organ(cid:173)
`isational intranet, performance can be excellent, and economies
`of scale are driving down the cost of "well resourced" to the point
`that high-performance WWW services are within the reach of
`private individuals, and service provision has become a cottage
`industry. Overall resilience is very high, on the "ant's nest" prin(cid:173)
`ciple - individual WWW sites may fail, but the very large number
`of sites operational at any time, and the (literally) bombproof
`nature of the Internet means that almost all services are available
`almost all of the time.
`There is no question that the diversity on content services on the
`WWW would not have evolved had the technology been avail(cid:173)
`able only to a small number of large, capital-rich organisations.
`The key to the rapid development of rich content services has
`been the openness and the low cost of entry, which has released a
`huge amount of entrepreneurial energy, a point which I will
`return to in the context of communication services.
`Communication services on the WWW consist largely of elec(cid:173)
`tronic mail and form-based communication using the Common
`Gateway Interface (CGI). Improved compression techniques have
`made it possible to create Internet telephony applications, but the
`Internet was not designed to carry continuous media and the pub(cid:173)
`lic portion of the Internet does it poorly at present - it is difficult
`to sustain voice communications on a peak hour, point-to-point
`bandwidth of 28 bytes/sec (observed by the author on many occa(cid:173)
`sions). There is little doubt that new Internet protocols such as
`1Pv6 [19] and the Resource Reservation Setup Protocol (RSVP)
`[20] will improve the situation for isochronous traffic and the
`long-term future for Internet telephony looks good. Bridging
`between Internet Telephony and the PSTN is already being pro(cid:173)
`vided on a commercial basis, making it possible to terminate
`Internet telephone calls in the PSTN.
`The difficulty is that value-added communication services in the
`PSTN remain isolated from communication services on the Inter(cid:173)
`net, creating a problem for a large population of users with Inter-
`
`net connectivity for whom the plain old telephone is still the sine
`qua non of day-to-day business communications. The basic aim
`of communication services is to improve communication by han(cid:173)
`dling the exceptions - when you are out (voicemail), busy (call
`waiting), on another telephone (call forwarding), on the move
`(mobility services) and so on. Creating parallel communication
`services on the Internet and PSTN may have the opposite effect
`of making personal communication more difficult to manage
`(there are many more possibilities) and there is a strong argument
`in favour of merging the two worlds.
`
`4.0 Two Worlds
`
`If the WWW has a dual (in the mathematical sense), or a foil (in
`the dramatic sense) then it is communication services, repre(cid:173)
`sented by IN. IN has many strengths and many flaws. Its strength
`is that many services are successfully deployed, such as 800
`number services, credit card calling, virtual private voice net(cid:173)
`works, voicemail, and various call waiting and redirection· ser(cid:173)
`vices.
`IN's primary flaw is that despite years of standardisation, services
`are implemented one-at-a-time on proprietary platforms. Switch
`vendors (who have little commercial motivation to open up their
`switches) are still lagging behind the standardisation process. IN
`systems do not scale well, and tend to be implemented using a
`mainframe mentality - huge, fault-tolerant SCP systems which
`provide services for hundreds of thousands or even millions of
`subscribers and take years to deploy. The networks used to sup(cid:173)
`port these services also support normal telephony, so anything
`attached has to be rigorously vetted. Despite years of standardisa(cid:173)
`tion, each country tends to have local variations of international
`standards, making it difficult to sell standard products into this
`market. Given the importance of standards in the telecoms indus(cid:173)
`try, this may seem surprising, but until recently, telecoms was
`dominated by state PTTs large enough to propose national varia(cid:173)
`tions, and despite the grindingly slow and thorough nature of ITU
`standardisation, interoperability is complex - even SS7 and
`TCAP, the foundations ofiN, have significant ANSI variations. A
`major deficiency is the poor integration between fixed and mobile
`telephony services - the popular GSM standard for mobile tele(cid:173)
`phony was founded on ideas taken from IN, but it is a closed
`architecture and it is possible for a person to have separate ser(cid:173)
`vices for their domestic and mobile telephone with no way to
`integrate the two.
`Service creation in IN is the precise dual of the WWW in that it is
`closed, and the cost-of-entry is very high and limited to a rela(cid:173)
`tively small number of highly capitalised corporations.
`Telecommunications companies believe that a next-generation
`architecture will support both advanced telephony services and
`new services such as video dial-tone, integrated fixed and mobile
`services, and content services such as video-on-demand (VOD),
`distance learning, and home shopping and banking. It is possible
`that the architecture-of-the-future will emerge from the TINA-C
`consortium, but there is also a competing claim in the telecom(cid:173)
`munications industry that IN will evolve from being an architec(cid:173)
`ture for telephony services into an architecture for broadband
`
`Bright House Networks - Ex. 1026, Page 3
`
`

`
`services [14] [15]. The model is that these services will be devel(cid:173)
`oped and deployed in the same closed manner as IN, by a small
`number of highly capitalised corporations.
`The issue at stake here is the future of integrated content and
`communications services, the point of convergence for both IN
`and the WWW. Will these services be provided in the manner of
`WWW content services - open, highly decentralised, hosted by
`low-cost commodity platforms, and subject to intense entrepre(cid:173)
`neurial competition and Darwinian evolution - or will they be
`provided in the manner of IN services - closed, centralised, with
`capital-intensive bespoke implementations and a slow rate of
`deployment and evolution.
`A belief underlying the work described in this paper is that the IN
`industry has to embrace the service creation philosophy of the
`WWW in the long term. There is already a recognition that cus(cid:173)
`tomers are looking for better service integration, for more com(cid:173)
`plex personal mobility services, for easier service configuration
`and customisation - the explosion of activity on the WWW is a
`demonstration of how far customers are prepared to go in person(cid:173)
`alising organisational and personal WWW sites, and how far the
`IN industry is from achieving these goals. The level of interest in
`Internet telephony will add further pressure to bring the WWW
`and PSTN closer together.
`The solution presented in this document for a converged content
`and communication service architecture, appropriately called
`Web IN, is to take the service architecture of the WWW and com(cid:173)
`bine it with the control architecture from IN.
`
`5.0 Web/N Physical Architecture
`
`5.1 Outline
`WebJN1 integrates these converging technoJogies by identifying
`the Service Data Function in IN with a personal or organisational
`virtual presence (i.e. WWW. home pages). The SDF in IN termi(cid:173)
`nology, the repository of communication service subscriber and
`subscription information, is removed from the closed SS7 net(cid:173)
`work and relocated and physically distributed on the open
`WWW, where it becomes identical with a WWW site. In prac(cid:173)
`tice, a person can be identified both within the telephone net(cid:173)
`work2 and on the WWW by a URL or URN. The physical
`architecture for WebiN is shown below in Figure 2., which shows
`the Service Control and Switching functions in the PSTN com(cid:173)
`municating with a Service Data Function physically distributed
`across WWW servers.
`The link between the worlds of telephony and the WWW is an
`Address Translation Database linked to the SCF which can trans(cid:173)
`late telephone numbers into URLs. This provides the link
`between a telephone number (which could be a portable personal
`number) and personal service data in a geographically dispersed
`SDF. An implementation of this database using the Internet
`Domain Name System is briefly described below. This associa-
`
`1. I am grateful to Nicolas Bouthors, Nicolas Raguideau and David Skov for sug(cid:173)
`gesting this name.
`2. This applies also to future switched technologies such as ATM. but for simplic(cid:173)
`ity I refer to the telephone network only.
`
`75
`
`Q
`~~ --.....
`( SCF)
`.._-
`
`SCE/SMS
`
`Service
`Data
`Function
`
`Service
`Control
`Function
`
`Service
`\..w.-iUSwitching
`Function
`
`Figure 2. WebiN Physical Architecture
`
`tion between telephone numbers and URLs means that you can
`obtain your telephone services even when you are not on the
`WWW The combination of an SCF with a WWW compliant SDF
`and an Address Translation Database we term a WebSCP (see
`also below in Figure 3.)
`The architecture in Figure 2. can be viewed in two ways: as an
`extension to the WWW which permits WWW services to control
`telephony, or as a modification to IN where service creation, ser(cid:173)
`vice data, and much of service management have been moved
`from a closed network (SS7) to an open network. I believe it is
`important to hold on to both interpretations, because they have
`very different commercial implications, and throughout the paper
`I will retain this dual IN/WWW perspective, switching between
`the two viewpoints, even though only one technology is being
`described.
`
`5.2 Communication Scenarios
`The types of communication envisaged are shown below in Fig(cid:173)
`ure 3. Users A and B are assumed to have connectivity to both a
`signalling network (Internet, enterprise intranet) and a bearer net(cid:173)
`work (PSTN, ATM ... ). Users C and D have connectivity only
`with the bearer network, in this case the PSTN.
`Users A and B are shown with two terminals each, one for Inter(cid:173)
`net and WWW access, the other for telephony. They could be
`integrated (e.g. via TAPI), or, as is still the case for most people,
`they will not be. Various WWW servers are shown, acting as
`repositories for services and objects owned by User A and User B
`and Users C and D.
`Some of the kinds of interaction which are possible are:
`• User A uses WWW page interaction to set up a PSTN tele(cid:173)
`phone call between User A and any of Users B, C or D.
`• User C makes a PSTN telephone call to User D, and both Users
`c and D trigger IN-style telephony services hosted on WWW
`servers.
`• User B configures his service subscription using WWW inter(cid:173)
`action (we could imagine that User Dis in fact User B when he
`is using his mobile telephone).
`
`Bright House Networks - Ex. 1026, Page 4
`
`

`
`76
`
`TCP/IP
`(signalling)
`
`User HTIP
`Service Server
`Policies
`
`Service Data
`Service Data
`Service Data
`
`/
`
`-?"
`
`5.4 The Service Data Function
`The WebiN SDF is structured as shown below in Figure 4. A
`,.
`. ....
`! l-:ir;r.·k::- l.og.;r.. \
`~--·· ·_: .. "(
`.. •,
`\
`,\,, .~::.r.:. ·~.; :~-..,~;:.~ ... :: .· <'
`c.:;." .. l'•it•\.: I nnj••
`(
`! : ;,'"\rv1r,n Logn":
`·
`'-' :__ ... _:-·_:__ -·-~
`Service Loqic
`(electronic ml!il)
`)
`' - - - - --.,.
`Service Logic
`(active badge)
`
`,..._
`URLs
`
`.........
`
`·
`
`..._ ___ _
`
`)
`
`Translation
`
`Figure 3. WebiN Interactions
`
`User D
`
`Figure 4. The Service Data Function
`
`• User A uses an Internet telephony application, bridged onto the
`PSTN, to talk to User C.
`• User C dials User Ns Internet telephony application as if it was
`a normal telephone.
`Contact policy, that is, how a person wants contact attempts to be
`handled, can be unified because in this view contact services have
`been disassociated from a particular contact technology (e.g. tele(cid:173)
`phony), and the WWW becomes the unifying mechanism which
`integrates contact policy for a number of different technologies.
`The examples given above show three contact technologies -
`WWW pages, Internet telephony, and PSTN terminals, but
`clearly other technologies such as FAX, voicemail and email can
`be integrated in the same way.
`
`5.3 The WebSCP
`The WebSCP unites two worlds: the bearer channel world (voice
`telephony, video telephony) and the WWW. The WebSCP can do
`four things:
`• it can create bearer channel connections between terminals.
`• it provides a User-to-Network signalling interface into the
`PSTN or a private campus network, which allows Internet tele(cid:173)
`phony applications to initiate or receive calls from the PSTN.
`• it can translate telephone numbers into URLs (possibly via
`URNs).
`• it can retrieve and execute service logic from WWW servers
`using HTTP.
`What makes the WebSCP different from a normal SCP (as com(cid:173)
`monly implemented) is that service logic is not concentrated on a
`closed database - it is distributed across normal WWW servers
`and is maintained by users in the same way as they maintain their
`normal WWW pages. Service logic (which could be written in
`JAVA) can be embedded in WWW pages (or loaded from WWW
`sites as JAVA classes). Control is devolved to the users, who are
`free to construct telephony services of arbitrary complexity and
`integrate these with their existing content services.
`
`Uniform Resource Locator specifies an individual's communica(cid:173)
`tion service resources, and the resources themselves are distrib(cid:173)
`uted in the same way as an HTML page can seamlessly link
`geographically dispersed documents.
`A personal identifier in the telephony world (e.g. a 700 number
`[10]) is associated with a URL in the WWW world. The key to
`the scaling, resilience, location transparency and ubiquitous
`access properties of the We biN SDF is a fast, resilient, federated
`translation database attached to the SCF. An example of such a
`technology is the Internet's Domain Name Service (RFCs 1034,
`1035), and we have used an unmodified, public domain imple(cid:173)
`mentation of DNS (BIND) to host a scalable telephone number(cid:173)
`to-URL translation service. The hierarchical nature of telephone
`numbering plans lead to similar scaling properties in the database
`as in Internet Domain Names. In order not to impact the Internet
`with tens of millions more DNS entries, I assume the address
`translation database for telephone numbers would be distinct and
`maintained by telephony service providers.
`The ability of the SCF to carry out a personal identifier to sub(cid:173)
`scriber resource translation means that subscriber resources are
`disassociated from a specific SCF and a specific service, and it
`becomes possible to amalgamate personal service resources for
`several services (even across several service providers) by using
`Uniform Resource Locators, either in their current WWW instan(cid:173)
`tiation or in some evolutionary form.
`Service composition is not limited to wireline or mobile tele(cid:173)
`phony - content services, email services and location services
`(e.g. via an active badge) can become the basis for integrated ser(cid:173)
`vices. It is possible to integrate services across several service
`providers. I believe that the problems of authentication and secu(cid:173)
`rity posed by open access to service resources (this is of concern
`in telephony, where the closed nature of the signalling network is
`not entirely a bad thing) can be approached incrementally and are
`ultimately surmountable - this is addressed below. In the first
`instance, enhanced subscriber access for service configuration is
`certainly achievable.
`
`Bright House Networks - Ex. 1026, Page 5
`
`

`
`5.5 The Service Control Function
`The separation of the SCF and SDF leaves a minimal SCP-like
`
`77
`
`federated
`distributed
`
`Figure 5. The Service Control Function
`
`function which I have called the "WebSCP", shown above in Fig(cid:173)
`ure 5. The core function of the SCF is to map a personal identifier
`to a subscriber resource locator (via a DNS-like co-located data(cid:173)
`base), to trigger the execution of subscriber service logic (wher(cid:173)
`ever it happens to be located), and to provide call redirection
`through the switch control interface provided by the SSP. In this
`form the WebSCP can be provided (within the limitations of
`switch and protocol variations) as a standard product. The princi(cid:173)
`pal components are:
`• a resource protocol for interacting with the SDF (e.g. HTTP).
`• address translation (via DNS)
`• a (possibly minimal) Service Logic Execution Environment
`(SLEE).
`• a optional Communication Session Manager, to provide an
`external call-control interface.
`• an optional User-to-Network interface to support Internet tele-
`phony bridging.
`• an !NAP-style interface for switch controL
`The SLEE function can be minimal, as the possibility exists to
`locate the bulk of the service logic on a WWW site via the HTTP/
`CGI interface- some examples of this can be found in [16]. It is
`also possible to locate a SLEE in WWW browsers, so that WWW
`clients can interact with the PSTN directly through the Commu(cid:173)
`nication Session Manager (CSM) and the User-to-Network inter(cid:173)
`face.
`The CSM is modeled on the TINA-C CSM [17], which provides
`an abstract, uetwork-independent resource model for manipulat(cid:173)
`ing multi-party calls, and can certainly invoke something as sim(cid:173)
`ple a "connect(A,B)" where A and B are two parties on the
`PSTN. The CSM would need to be complemented by an adequate
`SCP-SSP interface- AIN 1.0 [18], is adequate, but is not widely
`implemented in switches. The more widely implemented CSOl
`can provide call redirection services but not third party call con(cid:173)
`troL
`
`The User-to-Network interface between Internet telephone appli(cid:173)
`cations and the PSTN would be modeled on the ISDN 1.451 [ 11]
`signalling interface.
`
`5.6 Service Logic
`There several plausible variants of the WebSCP. An idea pre(cid:173)
`sented in [16] is that the WebSCP implements a variety of num(cid:173)
`ber translation services by calling out to external service logic,
`which could be located on customer premises (this is very attrac(cid:173)
`tive for 800 number and call distribution services) and the local
`service logic is little more than external request followed by an
`interaction with the SSP to redirect the call.
`A version of the WebSCP presented here interacts much more
`dynamically with personal service logic and personal service
`data, and is the basis for the Nexus prototype described later in
`this paper.
`Viewing the WebSCP as a WWW device, a WebSCP combines
`the functions of a WWW server and client. It provides a normal
`WWW server interface and provides a library of CGI scripts
`which can be invoked to provide bearer channel provision. It is
`self documenting - its home page references its CGI library and
`provides instructions for using its CGI scripts to create connec(cid:173)
`tions. Users would normally insert references to these WebSCP
`scripts into their own scripts, which in turn would be invoked by
`other users browsing their pages.
`The WebSCP can also act as an HTTP client, and reference pages
`on other WWW servers. These pages are written in the WebSCP
`scripting language and contain event handling scripts for a user's
`terminaL When specified events are triggered, the WebSCP can
`"reach out" to any WWW server and pull in the user's Event
`Page. The Event Page contains routines with well-known names
`which are invoked by the WebSCP when an event occurs. An
`Event Page is registered with a WebSCP by a user using a normal
`HTML form interface.
`Just which events should be supported needs further study. Sup(cid:173)
`port for calling-party services suggests a need for a number of
`events triggered when a user picks up and uses their telephone.
`Events supported should be generalisable to any form of connec(cid:173)
`tion-based communication, and should not be tied to Plain Old
`Telephones. The AIN 1.0 "Originating Basic Call State Model" is
`probably too detailed - perhaps events as simple as "information
`collected" and "interrupt1" would be sufficient for a number of
`useful calling-party services.
`Connections would be created using a simplification of TINA-C's
`Connection Management Architecture [17], where the