VoIP glossary · Secure Real-time Transport Protocol
What is SRTP?
SRTP (Secure Real-time Transport Protocol) is the encrypted version of RTP, protecting call audio so it cannot be listened to if packets are intercepted.
SRTP explained
SRTP encrypts each voice packet with AES and adds an authentication tag so tampering is detected. The encryption keys are usually exchanged in the SDP using SDES, which is only safe when the SIP signalling itself is protected by TLS.
Encryption on a trunk protects the path between your PBX and the provider. Once a call leaves for the public phone network it travels over carrier interconnects that are generally not encrypted end to end, so SRTP is one layer of protection rather than a guarantee.
Example
A clinic enables TLS on port 5061 and SRTP on its trunk, so patient calls are encrypted across the internet between the clinic and the provider.
Put it into practice
Prepaid SIP trunks and wholesale routes from $200. Ask sales for rates or the NOC for a technical answer.