Troubleshooting Busy Extensions

In this post, we will show you how to find out why a call to another extension is failing, and 3CX is indicating that the called party is busy.

  1. Reproduce the problem by making a call to the extension number causing the problem.
  2. Load the 3CX Management Console.
  3. Go to the “Server Activity Log” node.
  4. At this point, you have two options – filter by one of the extensions or filter by the Call ID. Generally, filtering by the Call ID gives more logging, however the Call ID may be more difficult to locate on a busy PBX. In our case, let us go ahead and filter using the calling extension, which produces the following logging. Remember to start reading the logging from the bottom, up:

    Leg L:3.1[Extn:101] is terminated: Cause: BYE from
    [CM503007]: Call(C:3): Extn:101 has joined, contact sip:101@
    L:3.2[VMail:999] has joined to L:3.1[Extn:101]
    [CM503025]: Call(C:3): Calling T:VMail:999@[Dev:sip:999@;rinstance=ac9743fb284af1b8] for L:3.1[Extn:101]
    L:3.1[Extn:101] forwards call from Extn:100 to VMail:999 based on rule Fwd[Available/Busy]
    L:3.1[Extn:101] failed to reach Extn:100, reason Busy
    Call(C:3):  from L:3.1[Extn:101] has failed, because Extn:100 is in DND mode
    [CM503001]: Call(C:3): Incoming call from Extn:101 to <sip:100@>

  5. The highlighted logging indicates that the call is not making it through because the called extension has DND enabled.

More Information

When an extension has DND enabled, 3CX Phone System treats the call as if the called party is busy and will forward the call using the configuration for Busy extension. In this case, the extension’s busy profile is configured to forward the call to the extension’s voice mailbox.

More information on the 3CX Server Activity Log and other examples on how this can be used for troubleshooting can be found here.

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