3 LANGUAGE FOR MODELING CALL PROCESSING SERVICES
DSM for CPL was implemented in small increments using existing IP telephony
service speci?¬?cations as test cases. These test cases were speci?¬?ed by the customer
and were partly available in the CPL speci?¬?cation itself (Lennox et al., 2004). In fact,
the implementation of the language was done in much the same order that the CPL
language was described in this original CPL speci?¬?cation documentation. After
adding the ?¬?rst few concepts to the modeling language, the generator was extended to
cover the same concepts. This allowed immediately making an equivalent service
speci?¬?cation with the DSM language and producing the CPL script for comparison
with the relevant test cases. This process was followed until all the modeling concepts,
and thus the full CPL speci?¬?cation, were handled.
The structure of the language was also taken directly from the CPL framework. The
XML schema provided the language concepts and many of the constraints. A call
processing action is structured as a tree that describes the operations and decisions a
telephony signaling server performs when a call is made. Each node in the tree has
parameters that specify the precise characteristics of the node. The nodes usually also
have outputs, which depend on the result of the decision or action.
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