The Voice AI Load Test Most Teams Forget: Call Closure

Voice AI load testing should assess not only whether calls connect at peak volume but also whether every call leg closes correctly, since abandoned SIP sessions can continue consuming AI concurrency, trunk channels, and contact-center ports. Proper closure requires caller, transfer, and AI legs to be released through SIP BYE/200 OK or CANCEL signaling, with all systems agreeing that the call has ended; transfers are especially vulnerable because missed hang-up signals, unsupported transfer methods, or custom routing logic can leave silent “phantom” calls active. The article recommends testing every termination path at peak rate, including caller and agent hang-ups, successful and failed cold or warm transfers, hold abandonment, and silence timeouts, then running a drain test to confirm that active-call counts return to zero across the AI platform, SBC, carrier, and contact center. Teams should reconcile call and transfer webhooks, inspect ongoing calls and SIP packet captures for signaling failures, monitor mismatches between call volume and concurrency after launch, and use timeouts, duration caps, and transfer ring limits to contain the impact of failures. It also advises making successful post-test concurrency drainage a release requirement and obtaining clear vendor and telephony-team commitments about hang-up propagation, SIP transfer support, port release behavior, and diagnostic access.

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