SRTP, or Secure RTP, is a protocol used for encrypting audio information in VoIP communications, specifically with Twilio's SIP domains and Elastic SIP trunks. It uses TLS encryption to protect the media stream from eavesdropping, replay attacks, and payload integrity issues. SRTP is essential for securing sensitive communications, especially when dealing with the Publicly Switched Telephone Network (PSTN), which does not support encryption. By enabling SRTP, users can mitigate the risk of data exposure and ensure that their VoIP calls are secure. The protocol adds negligible overhead to VoIP processing and has no observable effect on call quality. Implementing SRTP requires configuration on both the Twilio side and the user's SIP device, with varying levels of complexity depending on the device and network environment.