When the IP Office receives a SIP call, it determines the routing of the call as follows:

1. Line Matching:

   The incoming SIP call is matched to a SIP line. If no match is found, the call is ignored. SIP line matching is done in two stages:

   1. Protocol Matching:

      The call is matched with lines configured with the same protocol (UDP, TCP or TLS) and listening port settings.

   2. Line Association:

      If there are several possible line matches, they are checked in Line Number order, for a match between the incoming call's source and each line's Association Method setting.

2. Line Call Details Matching:

   Using the line's Call Routing Method, either the To or Request-URI of the incoming SIP request is used to find a matching Local URI.

   • The IP Office first looks for a matching SIP Line Appearances. If a match is found, the call is associated with the first available line appearance number in the Incoming ID order setting.

   • If no SIP Line Appearances match is found, the IP Office checks the line's SIP URIs in their URI number order.

   • Entries at their Max Session or Incoming Sessions values are ignored.

   • When an match is found, its Incoming Group ID setting is used for incoming call route matching. For SIP Line Appearances, this is in addition to altering on matching line appearance buttons.

   • If no match is found, the IP Office uses its Service Busy Response setting (486 Busy here or 503 Service Unavailable) to end the call.

3. Incoming Call Route matching:

   The IP Office's incoming call route entries are checked for a match.

   1. The matching uses the following options in order:

      1. Line Group Match:

         Only incoming call routes with a Line Group ID setting that matches the SIP lines appearance/SIP URI's Incoming Group ID setting are checked.

      2. Incoming Number Match:

         The IP Office looks for call routes with a match between their Incoming Number setting and the Local URI value received. There is always a received number value with incoming SIP calls, so always a potentially incoming number matching value.

         • Incoming calls routes with a blank Incoming Number field match any incoming number.

         • If the incoming call route's Destination is set to . (period), the Local URI received is used to look for destination matches.

           • If set to Auto, the IP Office looks for a matching extension number or system short code.

           • If set to Use Internal Data, the system looks for a match against the SIP Name of users and then groups.

      3. Incoming CLI Match

         From the possible matches, the IP Office looks for a match between the each route's Incoming CLI, if set, and the caller details in the From header. For SIP URI and TEL URI headers, partial matching starting from the left is supported. For IP addresses, only exact matches are supported.

   2. If the call matches more than one incoming call route:

      1. The most precise match is used. For example, the highest number of matching criteria and highest number of exact digit rather than wildcard character matches.

      2. If the call stills matches more than one incoming call route, the one added to the configuration first is used.

   3. If there is no match:

      1. For calls using a line's SIP URI entry with its Local URI set to Auto, the incoming number is checked for a direct match to an internal extension number.

      2. Otherwise, busy indication is sent to the caller and the call is dropped.

4. Incoming Call Route Match:

   Once a match is resolved, this determines the incoming call route’s current destination:

   1. Each incoming route can include multiple pairs of main and fallback destinations.

   2. Apart from the default pair, each pair uses an associated time profile. The time profile defines when that destination pair should be used.

      1. With multiple destination pairs, the entry used is the first, working from bottom up, whose time profile is currently 'true'. If no match occurs, the Default Value options are used.

      2. The system attempts to present the call to the destination. If the destination is busy, it presents the call to the fallback extension.

5. Call Presentation:

   The call is presented to the destination. If the call was routed via a SIP Line Appearance, the call also alerts on any matching Line Appearance buttons.