SIP transfer

A SIP transfer is a method used in Voice over IP (VoIP) systems to move an active phone call from one participant or system to another using the Session Initiation Protocol (SIP). SIP is the signaling standard that controls how calls are started, managed, and ended over the internet. SIP transfers allow calls to change hands smoothly without forcing the caller to hang up and start over.

In customer service environments, SIP transfers are essential for routing calls between AI voice agents, human agents, departments, or even external phone numbers while preserving call continuity.

How SIP transfer works

During a SIP transfer, the system sends SIP signaling messages that instruct the call to be redirected. This usually involves a SIP REFER message, which tells the receiving endpoint where the call should go next. Depending on the setup, the original agent may stay on the line briefly or disconnect immediately after the transfer is completed.

There are multiple transfer types, including blind transfers and attended transfers. In practice, teams choose between blind and attended transfers based on experience goals. Blind transfers move the caller immediately, which is fast but risky if context is missing. Attended transfers let an agent or AI briefly introduce the call and share context. This extra step often reduces repeat explanations and improves first-call resolution.

How SIP transfers enable seamless escalation in AI customer service

AI voice agents are often the first point of contact for incoming calls. While they can handle many requests, some situations require a human agent, such as billing disputes or emotional conversations. SIP transfers make these handoffs seamless, reducing frustration and call abandon rates.

SIP transfers also enable intelligent routing. An AI system can determine intent, gather context, and transfer the call to the most appropriate agent or team. This supports human-in-the-loop workflows, where AI and humans resolve issues faster via real-time collaboration.

As AI voice agents become more capable, SIP transfers will act less like simple call handoffs and more like coordinated transitions. Future systems will pass rich context—intent, sentiment, and history—alongside the call itself. The result is smoother collaboration between AI and humans, where transfers feel intentional rather than disruptive.

Common SIP transfer scenarios

Seamless call transitions are essential to maintaining a smooth customer experience. SIP transfers play a critical role in ensuring that conversations move efficiently between systems and teams without disrupting context or call quality. SIP transfers are widely used across customer service operations:

• Transferring calls from AI agents to live agents
• Routing callers to specialized departments
• Escalating issues to supervisors
• Forwarding calls to third-party vendors or partners

These scenarios depend on SIP’s ability to preserve call state and context.

Operational considerations for SIP transfer

Designing reliable SIP transfers requires attention to several factors:

• Call quality and latency during handoff
• Context sharing, such as conversation transcripts or intent detection
• Fallback behavior if a transfer target is unavailable
• Security controls to prevent unauthorized redirection

Without these safeguards, SIP transfers can fail silently or degrade the customer experience. When designed well, however, they form the backbone of scalable, AI-powered voice support systems.