Call Control
The dial plan stack
Calls are routed by digit analysis against the calling device's CSS, an ordered list of partitions holding patterns: directory numbers, route patterns, translation patterns, and wildcard patterns. The most specific match wins; among equally specific matches, partition order in the CSS decides. The standard ladder is route pattern to route list to route group to gateway or trunk. A route group distributes calls across its members, a route list applies the groups in order, and a route pattern selects the list.
Numbers and globalization
- E.164 globalization: normalize on ingress with translation patterns or device prefixes, route internally on E.164 with the plus prefix, then localize at egress. The classic trap is forgetting to localize before the PSTN gateway.
- AAR reroutes to the PSTN when CAC blocks a WAN call; it requires AAR groups and an AAR CSS, and must be tested rather than assumed.
- Time-of-day and holiday routing live on partitions plus time schedules, not on the route pattern alone.
Coverage and mobility
Hunt pilots, line groups, call coverage (forwarding to a DN, voicemail, or another coverage point), shared lines, device mobility (device mobility groups and physical locations), and Extension Mobility appear together in scenarios. Extension Mobility is login-based; device mobility follows where the phone is plugged in - a frequent mix-up.
Worked example
A user dials 91234 and hears reorder. Verify that the CSS on the line (not just the device) can reach the partition holding the translation or route pattern, that the pattern length matches the dialed digits, and that no higher-priority pattern in an earlier partition is intercepting the call.