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SIP (Session Initiation Protocol)

Updated 2026-09-30 · By the ZuteSIP team (ZuteSIP Inc.)

Short answer: SIP, the Session Initiation Protocol, is the IETF signalling standard defined in RFC 3261 that sets up, modifies and ends voice and video calls over IP networks. It handles who is calling whom and how; the audio itself travels separately over RTP. Any SIP-compliant app can use a ZuteSIP number.

Almost every business phone system, softphone and VoIP provider speaks SIP, which is why a SIP account works across so many different apps.

Definition

SIP is a text-based protocol, similar in style to HTTP, whose requests (REGISTER, INVITE, BYE and others) tell servers where a user can be reached and set up or tear down a call session.

How it works

  1. Your app sends REGISTER to the provider's SIP server and proves its identity with digest authentication.
  2. To call, it sends INVITE with an SDP body listing supported codecs.
  3. The other side answers, both agree a codec, and audio flows as RTP packets.
  4. Either side sends BYE to end the call.

How it applies to ZuteSIP

Every ZuteSIP number includes its own SIP username and password, shown on the number's page in the dashboard. Register to sip.zutesipdialer.com on UDP/TCP port 5060 or TLS port 5061, with G.711 µ-law or A-law and DTMF via RFC 2833 or SIP INFO.

Server:   sip.zutesipdialer.com
Port:     5060 (UDP/TCP) or 5061 (TLS)
Username: <SIP_USERNAME>
Password: <SIP_PASSWORD>
Codecs:   PCMU, PCMA

ZuteSIP SIP ports and transports

TransportPortServer
UDP5060sip.zutesipdialer.com
TCP5060sip.zutesipdialer.com
TLS5061sip.zutesipdialer.com

Common misconception

SIP does not carry the voice itself, and it is not a phone number. A SIP account is the login; the phone number is what callers dial to reach it.

Related terms

  • SIP trunk
  • Softphone
  • Codec G.711
  • DTMF
  • NAT and STUN

Frequently asked questions

Is SIP the same as VoIP?

No. VoIP is the general idea of voice over IP networks; SIP is the most widely used protocol for setting those calls up.

Which SIP apps work with ZuteSIP?

Any SIP-compliant software, including Zoiper, Linphone, MicroSIP, Bria, Groundwire, Asterisk, FreePBX, 3CX, FusionPBX and VICIdial.

Does ZuteSIP support SIP over TLS?

Yes, on port 5061. Plain UDP and TCP are on port 5060.

Is the audio encrypted?

TLS protects the signalling. SRTP media encryption is not part of the service.

Related pages

Sources