After the root element, other modeling concepts were call
processing concepts that usually pointed to the next stage in the call path. This service
?¬‚ow forms a tree structure and ends when the last element in the chosen path is
reached. Constraints were given to prevent cyclic structures as discussed later in
Section 5.3.2. The modeling concepts were divided into four categories based on the
classi?¬?cation of their nature already found in the CPL framework: signaling
operations, switches, locations, and nonsignaling actions.
Signaling Actions Signaling actions cause events that a CPL server can
perform. A server can proxy a call setup, respond with redirecting information, or
reject a call setup. Depending on the signaling action, different properties must be
de?¬?ned. To guide this, CPL speci?¬?es its own attributes for each action type. These
are added to the modeling language as their own constructs. The concept de?¬?nition
needed for the modeling language construct could be taken directly from the XML
Document Type De?¬?nition (DTD). Consider the following case of Proxy de?¬?nition
in the DTD:
output exists. - ->
timeout CDATA #IMPLIED
recurse (yes|no) ??™??™yes??™??™
ordering (parallel|sequential|?¬?rst-only) ??™??™parallel??™??™
>
This piece of DTD speci?¬?es that a proxy concept has three properties.
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