Session border controller

SIP trunking, short for Session Initiation Protocol trunking, carries voice calls over an IP network between a contact center platform and a telephony provider. It replaces physical PRI or analog phone lines with a virtual connection, sized by concurrent call capacity and codec choice. For an AI voice agent, the trunk is where audio enters and leaves the system. Codec quality, jitter, and capacity limits all directly affect how natural the agent sounds and how quickly it responds. Trunk health ties directly to latency, since a congested trunk adds delay before the agent even starts processing audio. Example: provisioning a dedicated test trunk and phone number lets a team run a proof of concept with OnClarity’s AI agents answering live calls, before wider rollout across the rest of the queue.

Failover is the automatic switch from a primary system, carrier, or data center to a standby one when the primary fails. Calls keep connecting without manual intervention. Active-active setups run multiple systems simultaneously, so traffic shifts instantly. Active-passive keeps a standby idle until the primary goes down, which takes longer to engage. Planning relies on two metrics: Recovery Time Objective (RTO), how fast service must resume, and Recovery Point Objective (RPO), how much data loss is tolerable. At the carrier level, failover reroutes inbound calls to a secondary SIP trunk or region. Example: a data center outage hits, and calls automatically reroute to a second region. Customers already in queue stay on the line instead of waiting for an engineer to trigger a manual disaster-recovery process.

Concurrent calls are the number of voice sessions active at the same instant, not the total calls handled in a day. This figure, not average volume, determines how many SIP trunking channels and licensed voice seats a contact center needs. Capacity has to cover peak moments, not typical ones. When active sessions reach the provisioned limit, new callers hit busy signals or route to queue overflow until a line frees up. Example: a utility’s power outage triples concurrent calls for twenty minutes. Capacity has to be sized well above daily average volume to handle that spike.