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What Is RTP and SRTP? Securing Voice Media in VoIP

RTP carries the actual voice in a VoIP call; SRTP encrypts it—so if you secure SIP (signaling) but not RTP (media), your conversations can still be intercepted.

Definition: RTP (Real-time Transport Protocol) delivers audio/video streams; SRTP (Secure RTP) adds encryption, message authentication, and replay protection on top of RTP.

RTP vs SRTP

RTP SRTP
Content Plain audio packets Encrypted audio
Security None Confidentiality + integrity
Use case Trusted LAN WAN / public internet / compliance

How media flows

SIP sets up the call and agrees on codecs and ports; RTP then streams the encoded voice (e.g., G.711/G.729/Opus) between endpoints. SRTP wraps those packets so only the endpoints can decode them.

When you must use SRTP

  • Calls traverse the public internet or untrusted networks.
  • Regulated industries (finance, healthcare, government).
  • Remote/softphone users outside the office.

Newrock perspective

Newrock OM-series and SBC support SRTP end-to-end and can enforce encrypted media policies, complementing SIP TLS for full call security.

FAQ

Does SRTP slow calls?

Negligible on modern hardware; the security benefit far outweighs tiny overhead.

Is SIP TLS enough?

No—TLS protects signaling only; SRTP protects the audio itself.

Do both ends need SRTP?

Yes; negotiate it in SDP. Mismatched settings cause one-way or no audio.

What about ZRTP?

ZRTP is another key-agreement method for media; SRTP is the encryption, often paired with SDES or DTLS.

Conclusion

Secure VoIP means securing both signaling (SIP TLS) and media (SRTP). Skipping SRTP leaves the conversation exposed exactly where it matters most.

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