What Is SIP?

Q: How does SIP relate to VoIP

SIP is the most widely used signaling protocol in VoIP, handling call setup and teardown. RTP carries the actual voice.

Q: How is SIP different from H.323

H.323 is an older ITU signaling protocol. SIP is an IETF standard, simpler and more extensible, and dominant in modern VoIP.

Q: What ports does SIP use

5060 for UDP/TCP and 5061 for SIP over TLS (Secure SIP).

2026-05-07 2 min readSIPPER Team

SIP is an application-layer protocol for initiating, modifying, and terminating real-time communication sessions like voice, video, and messaging over IP networks. Defined in RFC 3261.

Definition

SIP (Session Initiation Protocol) works similarly to HTTP, using methods (INVITE, ACK, BYE, REGISTER) and status codes (180 Ringing, 200 OK, 486 Busy). The actual audio travels separately over RTP / SRTP.

Usage

SIP is the primary VoIP protocol worldwide, connecting IP phones, softphones, IP PBX, Cloud PBX, SIP Trunks, and SBCs. It operates on port 5060 (UDP/TCP) and 5061 (TLS).

Related Concepts

SIP pairs with SDP (Session Description Protocol) to describe codecs and media paths, and RTP to deliver audio streams.

Frequently Asked Questions

How does SIP relate to VoIP

How is SIP different from H.323

What ports does SIP use

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