SIP

100 Trying

The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.

On this page

When You See This Code

Immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.

How to Fix

No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.

Specification

View RFC / Specification →

Compare With

180 Ringing 181 Call Is Being Forwarded 182 Queued 183 Session Progress 199 Early Dialog Terminated 200 OK 202 Accepted 204 No Notification 300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily 305 Use Proxy

Guides

401 Unauthorized vs 403 Forbidden: When to Use Each Security & Authentication

SIP Response Codes: Understanding VoIP Call Flow Real-Time Protocols

SIP Call Flow: Understanding Session Setup Real-Time Protocols

WebRTC Signaling with SIP and WebSocket Real-Time Protocols

RFC 3261: SIP Protocol Deep Dive Protocol Deep Dives

TLS 1.3: Faster, Simpler, More Secure Protocol Deep Dives

Specifications

RFC 3261 SIP: Session Initiation Protocol

RFC 3262 Reliability of Provisional Responses in SIP

Glossary

Status Code Request Method (HTTP Verb) TLS Handshake Authentication TCP/IP Port Number NAT (Network Address Translation) Socket Request-Response Model RFC (Request for Comments) Connection-Oriented Full-Duplex SRV Record SIP Dialog Signaling SIP Registrar STUN (Session Traversal Utilities for NAT) TURN (Traversal Using Relays around NAT) SDP (Session Description Protocol) SIP INVITE SIP Proxy Server SIP Redirect Server SIP Transaction SIP User Agent SIP Trunk RTP (Real-time Transport Protocol) SRTP (Secure Real-time Transport Protocol) SIP ACK SIP BYE SIP CANCEL SIP OPTIONS SIP SUBSCRIBE/NOTIFY B2BUA (Back-to-Back User Agent) SBC (Session Border Controller) Codec Negotiation SIP Response Classes VoIP (Voice over IP) Presence (SIP) PBX (Private Branch Exchange) MFA (Multi-Factor Authentication) TLS Versions

Frequently Asked Questions

What is SIP 100 Trying?

The request has been received by the next-hop server and an unspecified action is being taken to process it. The UAC should expect additional responses.

When do you see SIP 100 Trying?

Immediately after sending an INVITE. The proxy has received the call and is searching for the callee. This is the SIP equivalent of a dial tone.

How to fix SIP 100 Trying?

No fix needed — this is normal call setup behavior. If stuck on 100 Trying for too long, check network connectivity and proxy configuration.