Decision framework
Give every SIP trunking provider the same deployment brief.
A SIP trunk quote can look simple while leaving important design assumptions unanswered. The provider may not know whether the trunk will connect to an IP PBX, softswitch, SBC, dialer or communication application, how many calls will be active, how quickly new calls are attempted or which numbers and destinations are required.
A written requirements checklist lets technical and commercial teams compare providers using the same scope. It also becomes the starting point for configuration, testing and the operational handoff after launch.
01 / Platform
Map the PBX, SBC and network connection.
Identify every system that will send or receive calls and the network boundary between your environment and the provider. A high-level call-flow diagram is often more useful than a product name alone.
Voice platform
Record the PBX, softswitch, SBC, dialer or application name, software version, deployment location and technical owner.
Authentication and addressing
State whether the connection needs IP authentication or registration, list public signaling and media addresses and describe NAT or firewall behavior.
Media behavior
Confirm allowed codecs, DTMF method, fax requirements, encryption expectations and any media anchoring or transcoding in the call path.
Practical check: Include both signaling and media flows in the diagram; a successful SIP registration does not prove that two-way audio will pass correctly.
02 / Capacity
Size concurrent calls and calls per second separately.
Concurrency measures active call legs. CPS measures how quickly new calls are attempted. An office PBX with long conversations may need meaningful concurrency but modest CPS, while a dialer can create short bursts that require a higher call-attempt rate.
Use busy-hour observations where possible. Include inbound and outbound demand, transfers, forwarded calls, conferences and growth headroom because each call flow can consume capacity differently.
Concurrent call paths
Record the current peak, expected launch peak and planned growth for inbound, outbound and combined active calls.
CPS and burst pattern
Document normal and burst call attempts per second, campaign start behavior and any automatic redial or application-generated traffic.
Bandwidth and quality
Estimate available network capacity by codec and include latency, jitter, packet-loss monitoring and voice-priority controls in the local network plan.
Practical check: Ask how the provider measures and enforces capacity, and what happens when the configured CPS or concurrent-call limit is reached.
03 / Call flows
Define destinations, DIDs and caller identity.
Inbound and outbound scope should be explicit. List the countries called, the DIDs received, the caller ID presented and any routing logic that depends on location, business hours or failure conditions.
Outbound routing
List destination markets, expected minutes, call purpose, caller ID format and whether any routes need distinct quality or commercial treatment.
Inbound numbers
Identify new or ported DIDs, number types, expected concurrent calls, target SIP destinations and market-specific documentation.
Regulatory responsibilities
Clarify number-use rights, emergency-calling scope, caller ID rules, recording obligations and other responsibilities that apply to the deployment markets.
Practical check: Do not assume a number, emergency feature or caller ID behavior is included because it is available in another country or on another trunk.
04 / Launch
Agree on acceptance tests, failover and support.
A production cutover should test normal calls and failure conditions. Define who changes routing, how the secondary path is triggered, what monitoring is visible and how both teams communicate during the launch window.
Acceptance tests
Test inbound and outbound completion, CLI, DTMF, transfers, hold, forwarding, voicemail, audio, SIP responses and the specific flows users depend on.
Resilience
Document secondary endpoints, DNS or IP behavior, rerouting triggers, timeout expectations and how service is restored to the primary path.
Commercial and support handoff
Confirm capacity charges, usage rates, number fees, change lead times, support hours, severity levels and escalation contacts.
Practical check: Run a controlled failover test before launch and record the observed behavior rather than relying only on the intended design.
Ready-to-send brief
SIP trunking requirements checklist
Send these details with the request for proposal or technical review.
- Business use case, locations and intended launch date
- PBX, softswitch, SBC or application name and version
- Public signaling and media IP addresses plus firewall or NAT notes
- IP authentication or registration requirement
- Supported codecs, DTMF method and any fax or encryption needs
- Peak concurrent calls for inbound and outbound traffic
- Normal and burst calls per second with growth expectation
- Outbound countries, monthly usage and caller ID plan
- New or ported DID markets, number types and quantities
- Primary and secondary routing or failover design
- Acceptance-test cases and planned cutover window
- Technical, billing and emergency escalation contacts
Common questions
SIP trunk planning questions
What is the difference between SIP channels and trunks?
A SIP trunk is the connection between systems, while a channel or call path commonly represents one concurrent call leg. Provider terminology and charging models vary, so confirm exactly how concurrent capacity is defined.
How do I estimate SIP trunk capacity?
Start with observed busy-hour concurrent calls, inbound and outbound balance, transfers or forwarding, CPS bursts and planned growth. Review the result with the provider because call flows and charging models can consume capacity differently.
Should a SIP trunk use registration or IP authentication?
Both approaches are used. The right choice depends on the platform, network addressing, security model and provider support. Confirm firewall, failover and credential-handling requirements for the selected method.
What should be included in SIP trunk acceptance testing?
Test the actual inbound and outbound flows, caller ID, DTMF, transfers, forwarding, codecs, two-way audio, SIP responses, capacity behavior, failover and escalation process.