Characterizing Semantic Warnings of Service Description in Call Processing Language on Internet Telephony

The Call Processing Language (CPL, in short), recommended in RFC 2824 of IETF, is a service description language for the Internet Telephony. The CPL allows users to define their own services, which dramatically improves the choice and flexibility of the users. The syntax of the CPL is strictly defined by DTD (Document Type Definition). However, compliance with the DTD is not a sufficient condition for correctness of a CPL script. There are enough rooms for non-expert users to make semantical mistakes in the service logic, which could lead to serious system down. In this paper, we present six classes of semantic warnings for the CPL service description: MF, IS, CR, AS, US, OS. For each class, we give the definition and its effects with an example script. These warnings are not necessarily errors. However, these warnings will help users to find ambiguity, redundancy and inconsistency in their own service description.