Freeze one duplicated inbound attempt
Record one authorized inbound attempt with timestamp and timezone, called DDI, number block and base number, caller, every device that alerted, the intended PBX destination and the branch that answered. Preserve Control Page targets, provider-visible registrations and PBX contacts before deleting anything.
Define the symptom precisely. A&A documents that a number can target registered devices, a customer SIP server and Also Ring destinations. Two alerting branches may therefore reflect submitted policy rather than duplicate packet delivery or a PBX fault.
Inventory provider-side branches before the PBX
For the affected number and any inherited base number, list the effective target, every registered contact, the configured SIP-to-server hostname and port, each Also Ring destination and its delay. Record whether the old device registered against the called DDI, the base number or another number that is itself an Also Ring target.
A&A says direct SIP-to-server delivery does not require registration and that, when registration is also present, INVITEs may go to both. Removing a PBX endpoint does not remove a provider registration or Control Page branch.
Correlate each provider INVITE with one branch
Capture provider-visible call evidence and PBX SIP messages for the same timestamp. Compare destination URI, source server, Call-ID, Via branch, Request-URI and authentication behavior. A&A uses multiple servers selected through DNS, so different source addresses are not automatically separate unauthorized calls.
Decide whether the PBX received one INVITE while another branch rang outside it, or received more than one INVITE for distinct provider targets. Do not collapse a registered-device branch, direct server delivery and PSTN Also Ring leg into one contact list.
Follow answer, remote voicemail and cancellation
For every branch, record provider attempt, alerting, final response, answer identity, cancellation and media. A&A warns that remote voicemail on an Also Ring destination can answer unexpectedly because the provider cannot distinguish it from a person. A 200 response therefore proves that branch answered, not that the intended employee accepted the call.
If the PBX forks internally, retain its contact and bridge evidence separately. A handset display such as “answered elsewhere” can describe cancellation after another winner and does not identify that winner.
Correct only the demonstrated owner
If the old device remains provider-registered, revoke or replace the relevant SIP secret or remove the authorized registration using the supported account workflow. If the direct SIP target is unintended, change that target. If inherited base-number policy or Also Ring owns the branch, correct that object and preserve unrelated DDIs.
Do not broadly block provider addresses, disable all registrations or erase PBX contacts to mask an upstream target. A&A exposes registration IP and User-Agent information and supports source-IP restrictions and registration alerts; use those controls without publishing credentials or personal call data.
Retest the intended target graph and rollback
Retest the affected DDI, a sibling DDI that inherits the base target and one nearby number that should not match. Confirm the expected PBX branch, absence of the retired device, correct delayed targets, answer, losing-branch cancellation and two-way media. Then verify outbound service and any approved resilience path still work.
Record the effective Control Page state and provider-visible registration set after the change. This workflow is documentation-derived and was not reproduced on a customer or laboratory trunk.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- A&A: VoIP SIP Trunks ↗
- A&A: multiple inbound targets and Also Ring ↗
- A&A: VoIP technical information ↗
- A&A: VoIP security controls and registration visibility ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.