Plivo Zentrunk: inbound URI, fallback, logs and call evidence

Separate inbound and outbound trunk objects

Plivo documents separate inbound trunks for calls delivered to customer infrastructure and outbound trunks for customer-originated calls. Only an inbound trunk is linked to Plivo phone numbers and a customer primary or fallback URI. Outbound calling instead uses a termination domain plus an IP access-control list, credentials or both.

Zentrunk does not support SIP REGISTER. A missing registration indicator is therefore not evidence that the trunk is down. Preserve direction, trunk ID, number assignment, URI and outbound authentication as different objects.

Prove the number, trunk and URI chain

For inbound calling, begin with the dialed Plivo number and verify that it is linked to the intended enabled inbound trunk. Record that trunk ID, the primary URI, the optional fallback URI, each FQDN or IP address, URI authentication setting and the PBX route expected to accept the resulting INVITE.

A number in the account is not proof of assignment to this trunk. A saved URI is not proof that DNS resolved, the network accepted the packet, credentials matched or a PBX route answered.

Read fallback as an unresponsive-primary rule

The current quickstart says calls go to the primary URI first and are forwarded to the fallback URI if the primary is unresponsive. It does not publish a universal response-code matrix promising that every 4xx, 5xx or 6xx from the primary advances to fallback. Preserve no response, transport failure and each final SIP response as different outcomes.

For an authorized noncritical number, test a normal call, a deliberately unreachable primary, recovery and return to primary. Test a reachable primary that rejects the call separately. Do not call one successful fallback attempt a service-level or active-call continuity result.

Correlate provider logs with PBX and network evidence

Plivo debug logs expose call direction, timestamps, trunk ID and domain, secure-trunk status, transport, hangup source and cause, final SIP response, negotiated codec and a downloadable SIP PCAP. The hangup reference distinguishes customer, carrier and Zentrunk sources and includes URI, timeout, routing, authorization, capacity and media causes.

Use one call UUID and SIP Call-ID to align those records with PBX logging and, when authorized, a customer-side capture. Provider signaling PCAP is not proof of packets at the PBX interface, and a negotiated codec does not prove decoded two-way audio.

Keep capacity, protection, media and account facts independent

Plivo documents account-wide CPS and concurrency pools shared by SIP Trunking and Voice API, with additional outbound-trunk CPS. Calls above Zentrunk limits are rejected rather than queued, using hangup cause 5180 for CPS or 5190 for concurrency. Those limits are different from inbound URI reachability or PBX capacity.

The current specification lists PCMU and PCMA, RFC 2833 DTMF, TLS signaling and SRTP media. Secure Trunking state, transport, SDP, selected codec, RTP endpoints and both decoded audio directions still need separate evidence. Confirm current limits, data region, number inventory, port status, emergency workflow, regulatory eligibility, retention, support entitlement and rates through the authorized account and order. No account, number, trunk, URI, failover event, PBX, packet, protected session, codec, DTMF event, media stream, emergency workflow, price, availability or compatibility was tested for this guide.

Trace Plivo inbound URI selection into fallback

Use the Plivo inbound diagnostic to prove the number link, primary attempt, exact SIP result, fallback eligibility, PBX handling and media.