Public Switched Telephone Network (PSTN)
The Public Switched Telephone Network (PSTN) is the traditional, circuit-based telephone network that has powered voice communication for more than a century. It connects landlines, mobile networks, and international carriers through a system of physical phone lines and dedicated circuits. While much of today’s voice traffic is now carried over IP-based systems such as Voice over Internet Protocol (VoIP), the PSTN remains the global backbone for reliable, universally accessible voice communication.
How PSTN works
PSTN uses a circuit-switched architecture. When someone places a call, the network creates a dedicated, continuous electrical path between the two endpoints for the duration of the conversation. This physical or virtual circuit ensures clear, uninterrupted transmission without competing network traffic. PSTN calls travel through local exchanges and long-distance carriers, which route signals across copper wires, fiber networks, undersea cables, and cellular infrastructure.
Although many modern carriers have transitioned backend switching to digital systems, the fundamental concept remains the same: once a connection is established, bandwidth is reserved until the call ends. This differs from VoIP, where data travels over the internet in small packets and may share bandwidth with other types of traffic.
PSTN offers predictable routing and dedicated pathways, making it more stable and resilient than purely internet-based systems, especially during emergencies or when broadband connectivity is unreliable.
Why PSTN underpins AI-based customer service
PSTN continues to play a major role in customer service, particularly for organizations with large inbound call volumes. While omnichannel engagement continues to expand, many customers still prefer phone-based support, especially for urgent or sensitive issues. When AI-powered interactive voice response systems (IVRs) conversational agents interact with callers, they often must interface with PSTN connections.
This matters because PSTN imposes constraints that affect AI performance. For example, audio quality, signaling protocols, and timing expectations differ from VoIP or digital channels. When an AI system must interpret spoken input or generate responses in real time, these factors influence accuracy and speed. PSTN’s predictability can actually help stabilize some AI voice applications. However, its traditional signaling also limits certain advanced features without additional telephony infrastructure.
Moreover, PSTN’s widespread global availability ensures customer access in regions where internet-based calling is inconsistent. AI systems designed for service automation must therefore be able to bridge PSTN and cloud-based environments without degrading experience or reliability.
Considerations
Organizations deploying AI voice solutions over PSTN should account for several practical factors:
- Audio quality constraints: PSTN narrowband audio can reduce transcription accuracy unless speech models are trained or optimized for its frequency range.
- Timing differences: Circuit-switched signaling introduces different call setup and interaction timing than VoIP, which can affect real-time AI responsiveness.
- Interoperability requirements: Connecting PSTN to cloud-based AI platforms typically requires SIP trunks or gateways that can securely translate between PSTN and IP systems.
- Monitoring needs: Latency, call quality, and AI performance should be tracked continuously to ensure a seamless caller experience.
PSTN remains a critical part of global customer service infrastructure. AI systems that integrate effectively with PSTN can deliver more reliable interactions and maintain operational resilience even when digital connectivity varies.
