Andrews & Arnold SIP Trunks: registration, targets and DDI evidence

Identify the number, block and trunk direction

A&A describes every VoIP number as usable for SIP trunking, but the outbound and inbound directions can use different mechanisms. Record the customer account, full international-format number, any DDI block and base-number inheritance, the authorized PBX or SBC, service address, Control Page state and current order.

For outbound service, the PBX can register with the number and per-number SIP password. For inbound service, A&A can send calls to a configured SIP server with credentials that server expects. A registration, a SIP-to-server target and a forwarded PSTN number are different delivery contracts.

Resolve registration, DNS and direct server delivery

Capture the registrar name, DNS A, AAAA and SRV answers, transport, authentication identity, Contact, requested and granted expiry and every provider-visible registration. A&A documents multiple active servers and may change which servers DNS selects, so a PBX pinned to one cached address can diverge from the service name.

Then inspect the inbound target independently. A configured SIP-to-server hostname, port or IP does not require the PBX to register. If registration and direct delivery are both present, A&A says both can receive INVITEs; do not label a second call branch a duplicate until the intended target model is known.

Trace DDI, base-number inheritance and identity

For a number block, record the called DDI, its base or group setting, the effective inbound target and the exact Request-URI reaching the PBX. Individual numbers can inherit the base target while retaining separate management and billing, so the visible DDI and the authenticating base number may not be the same object.

For outbound calls, preserve the authentication number, asserted CLI, presentation-number setting, provider acceptance and destination-visible identity. Ownership of a DDI, use as a base number and authorization to present a CLI remain separate evidence.

Bound multiple targets, answer and failover

A number can have registered devices, a SIP server target and Also Ring destinations with optional delays. Inventory every active branch and its owner before changing the PBX. Remote voicemail can answer an external branch, so provider acceptance, alerting, answer, human confirmation, bridge and media must be recorded separately.

Multiple targets can improve new-call reachability, but they do not prove active-call survival, alternate capacity, answer confirmation, detection time or restoration. Exercise normal delivery, one approved failure, a nonmatching control number, recovery and return to primary.

Keep media, security and scale claims scoped

The published platform description covers G.711 A-law audio and SIP INFO or RFC2833 DTMF at the provider media endpoint. Preserve the actual SDP, payload mapping, RTP endpoints, both audio directions and decoded digits. Fax remains unverified until its own T.38 or audio-fax acceptance path is documented.

Use strong SIP passwords, source-IP restrictions, registration alerts, price limits and Control Page 2FA where appropriate, but do not turn those fraud and access controls into TLS or SRTP claims. An unlimited published channel count also does not prove PBX, bandwidth, credit or call-start capacity.

Accept commercial, support and emergency boundaries

Retain a dated order for number setup, rental, porting, destination rates, taxes, term and support. The public price page is a catalogue snapshot and not proof of an available number, completed port or selected account entitlement.

Document location and callback-number requirements, local power and Internet dependencies, customer equipment, provider fault exposure and an accessible alternative route. Coordinate emergency validation with the provider and relevant authorities; do not place an uncoordinated emergency call. No customer trunk or live call was tested for this guide.

Diagnose an old device ringing beside the PBX

When an A&A number alerts a retired device and the PBX, use the focused target-graph diagnostic. It separates provider registrations, direct SIP-to-server delivery, inherited DDI targets, Also Ring branches, answer and cancellation.