SIP Transfer

In practice, a SIP transfer is the process of moving an active voice call from one endpoint to another using the Session Initiation Protocol. SIP is the standard signaling protocol for internet-based voice communication, and a SIP transfer allows calls to be redirected, handed off, or bridged between systems — such as from an AI voice agent to a human agent queue, or from one contact center platform to another. The transfer can include call metadata, enabling the receiving endpoint to have context before the conversation continues.

A contact center deploys an AI voice agent to handle routine inquiries. When a caller's issue exceeds what the AI can handle, the system initiates a SIP transfer to route the call to a human agent. Along with the call, the system passes context about the caller's intent, the information already collected, and the reason for escalation. The human agent receives this context before the call connects, allowing them to continue the conversation without asking the caller to repeat themselves. Without SIP transfer, the escalation path would require the caller to be disconnected and redial, or accept a cold handoff with no context.

This shows up as the technical foundation for any AI-to-human handoff in voice-based customer operations. A well-implemented SIP transfer preserves call quality, passes context, and creates a seamless transition from automation to human handling. A poorly implemented one creates dead air, dropped calls, or cold handoffs that force customers to repeat themselves. For teams building or evaluating AI voice deployments, SIP transfer capability and context-passing quality are two of the most operationally significant technical considerations.