Parlay and mobile agents in a homogenized service provision architecture

This paper describes an innovative architecture for creation and provision of services running homogeneously over different networks. This primarily implies the fact that the service logic has to be independent of the underlying network. Until now, such convergence between public switched telephony network (PSTN) and Internet is achieved in the transport layer. This is the case of dial-up connection where the telephony access network is used to connect the Internet service provider with the user. This would be also the case when the telephony service providers are routing calls through IP networks to reduce costs. In these cases, only the lowermost layers are replaced and so the homogenization of provided services can be viewed less portentously. In the cases where service interworking takes place in a higher level (e.g. WAP in the application layer), the convergence is based on the implementation of proprietary gateways, which are usually suitable for specific situations. The nature of service creation and provision differs in PSTN and Internet. The PSTN is oriented towards the provision of telephony service and other call-related services. These services use the concept of a call, the establishment of which allows the exchange of bit streams between the parties participating in the call. Call-related services can be based to a call model similar to the basic call state model (BCSM), which has been described in the intelligent network (IN) specifications. Among different architectures aiming at the provision of advanced telecommunication services, IN is worldwide an accepted service control architecture. In this paper the term IN can be applied for telecommunication networks based on PSTN infrastructure. On the other hand, Internet is a generic packet switching network. Its services concentrate on the abilities and the intelligence of terminals. Nevertheless, Internet applications could not be described using a model similar to the BCSM. This happened due to the inability of intermediate nodes to maintain information about the state of a running service. This situation has been confuted by the Voice over IP (VoIP) protocols. The H.323, SIP and MEGACO protocols foresee entities like gatekeepers and media gateway controllers, whose functionality is to maintain call state information. Using these entities it is possible to build an IP (soft) switch that could perform tasks similar to the PSTN switches. The key issue to achieve a signaling interworking between PSTN and Internet is to apply the appropriate mappings between the protocols used in IP telephony and making sure that a common call state model is suitable for all of them. Since the call control protocol that is used from H.323 is the Q.931 the above prerequisite could be easily applied. The same happens with the SIP, where initiating call messages could be mapped to Q.931 using a signaling gateway that converts SIP messages to Q.931 and vice versa. This way signaling interworking has been achieved and the IN architecture is conveyed over IP networks.