Outbound Call Routing logic

3CX routes calls to SIP Trunks based on criterias the administrator defines in “Outbound Rules”. An outbound rule has a set of conditions which will trigger the rule, such as which user or department is calling, the dialed number, or the number length.  Once the conditions are met, each rule can have up to 5 routes which 3CX will use if one route fails to process the call. For example, if a SIP trunk is down or if it is at capacity.

Outbound rules are triggered according to their priority. So if you have 5 rules, and a previous rule has been triggered because the conditions were met, any subsequent rules will not apply. You can move outbound rules up or down in the Outbound Rules page.

Auto creation of Outbound rules

When you create a system wide SIP trunk you proceed to create an outbound rule for it. If the SIP trunk is created within a group and there is no other rule for that group, it will automatically create an outbound rule to route calls via the new SIP trunk. If there is already a SIP trunk and outbound rule configured you must create the outbound rule yourself, i.e. the SIP trunk will not be used unless you create a corresponding outbound rule that sets the route based on conditions you have defined.

Conditions are cumulative

IMPORTANT: If you specify Extensions and one or more Extension Groups then the rule will trigger if the extension is in the group OR in the list of extensions (so, cumulative).

Creating an Outbound rule

To create an outbound call rule:

1. Go to “Outbound Rules”, select “Add”, and enter a name for the new rule.
2. Specify the conditions which should trigger this outbound rule:

• Calls to numbers starting with prefix - Any numbers starting with for example “9”.
• Calls to numbers with a length of - For example 8 digits, to differentiate between local and national numbers.

3. You can make the rule for a specific extension in Calls from extension(s). Define the extension(s) or extension range separated by commas and ranges using “-”, e.g. 100,102-120.
4. You can also specify a whole department by clicking the Add button after Calls from departments.
5. Now in “Make outbound calls on” set the routes on which the calls should be placed. If the first route is not available or busy, 3CX automatically tries the next route, until the call can be made or the default “Block Calls” route is reached.
6. You can transform the number that matches the outbound rule, before the call is routed:

• Strip Digits - removes one or more digits from the called number, e.g. strip one digit to remove the prefix “9”, before the number is dialed.
• Prepend - add one or more digits at the beginning of the number, if this is required by the provider or gateway.

7. You can specify an ‘Outbound Caller ID’. 3CX will set the outbound caller ID although the telecom provider might disregard this outbound caller ID. See the event log for any errors if the outbound caller ID is not being shown on the call.
8. Click “Save” to add the outbound rule.
9. Now after the outbound rule is created it will be added to the bottom of the list, i.e. it has the least priority. If you want to increase the priority of an outbound rule you have to select it and click the “Move Up” button.

Selecting/Skipping Routes

• 3CX will select all available SIP Trunks and Bridges in order (1 to 5).
• In the case a SIP Trunk is unregistered (red) it is skipped immediately.
• Ringing (180 or 183) does not define a successful call and another SIP Trunk might be selected or the hunt will end accordingly upon receiving the SIP message.
• In case a SIP Trunk returns any of the following “busy” SIP messages the next route will NOT be selected and a busy signal will be sent to the internal caller immediately:

• 486 Busy Here
• 600 Busy Everywhere
• 1408 No Response (3CX internal error code)

• A call is considered “successful” when the following call states are reached and no further route will be selected:

• 200 OK  (Called Party Answered)
• Cancel (Calling Party ends the call before being connected)

Notes

• Early Media and Ringing - When using more than one route in a rule the processing of early media and ringing will change. As 3CX can not foresee that a selected route to the called party might still fail to another route, certain handling in the ringing state is altered in relation to early media processing (commonly SIP, 183 Ringing). After receiving 183 ringing messages, which is normally used to pass country-specific ringtones as an audio stream or early media info, such as “this call will cost $1 per minute”, these will be converted in 3CX to 180 and the “audio stream” will be dropped. Extensions cannot hear the early media announcement and/or IP phones will play the device's ringing tone instead of the media stream provided by the provider.
• IP Based SIP Trunks (Peering) IP based providers (peering) have no registration and therefore it is not possible for 3CX to determine if the SIP trunk is up or not. The result is always “green” and 3CX will try for each call to select the line before skipping to the next route.