SIP over WebSocket

Make Browser SIP Calls with SIP over WebSocket

Start the call from any browser tab. There is no download, and you only add a number to receive inbound calls.

Product facts

  • Outbound: No dedicated number required.
  • Inbound: Requires US/Canada digital number ($2.14 to $5/month).
  • No apps: Works in Chrome, Safari, Edge, Firefox.
How it works
Browser SoftphoneReady

What is SIP over WebSocket?

SIP over WebSocket wraps standard SIP signaling inside WebSocket frames so modern browsers can register as SIP clients. Combined with WebRTC media, it enables a true browser based telephony experience.

Browser Native

No plugins or downloads. Use Chrome, Firefox, Edge, or Safari to place and receive SIP calls directly from the web. StartACall handles the SIP over WebSocket client stack for you.

PSTN Reach

StartACall bridges WSS to Twilio and SIP trunks so your browser calls can reach any phone number worldwide. Manage virtual numbers and inbound routing from the dashboard.

AI and Analytics

Enable , live copilot assistance, transcriptions, and real-time analytics while using SIP over WebSocket to power smarter voice workflows.

How StartACall implements SIP over WebSocket

A typical call flow connects the browser to PSTN using secure WebSocket signaling and WebRTC media. StartACall orchestrates the components so you can focus on calling.

Step by step

  1. Browser creates a secure WebSocket (WSS) to StartACall signaling gateway.
  2. StartACall translates WSS SIP signaling to Twilio or your SIP trunk using standard SIP messages.
  3. Media is negotiated with WebRTC and routed through StartACall or Twilio as required.
  4. Calls reach PSTN numbers via Twilio bridging, and call events are reported back for analytics and AI features.

Developer friendly

StartACall provides tokens and SDKs to register browser clients using SIP over WebSocket. Integrate quickly and use webhooks for call events, recordings, and transcriptions.

Instant browser registration and dialing.
Global PSTN connectivity via Twilio and SIP trunks.
Secure WSS connections and SRTP media for privacy.

Security and Reliability

SIP over WebSocket runs over TLS, and StartACall uses SRTP for media. We integrate with Twilio and deploy hardened gateways to ensure call integrity and uptime.

Encrypted Signaling

WSS over TLS secures SIP messages between browser and gateway.

Secure Media

SRTP encrypts audio streams so media remains private.

Monitoring

Real time analytics for call quality and usage with alerts.

Common Use Cases

SIP over WebSocket unlocks new workflows for sales, support, and voice automation using just a browser.

Contact Centers

Agent consoles run in the browser with live AI assistance and call recording.

Remote Teams

Sales and support teams make secure PSTN calls from any device without softphones.

Voice Automation

Deploy to handle inbound or outbound SIP calls using StartACall voice AI stack.

Frequently Asked Questions

Is SIP over WebSocket supported by all browsers?

Modern browsers like Chrome, Firefox, Edge, and Safari support WebSocket and WebRTC. StartACall tests common configurations to ensure compatibility.

Do I need special ports open on my firewall?

SIP over WebSocket uses standard HTTPS ports when configured with WSS which minimizes firewall issues. Media uses RTP over standard ranges which StartACall documents for network configuration.

Can I use my existing SIP provider?

Yes. StartACall can bridge WSS SIP signaling to many SIP trunks and to Twilio so you can keep existing SIP infrastructure while enabling browser endpoints.

How do work with SIP calls?

StartACall can run autonomous voice agents for outbound campaigns or provide a live copilot during calls by transcribing audio and suggesting responses in real time.

Ready to run SIP in the browser?

Sign up and enable SIP over WebSocket for instant browser based calling, AI capabilities, and global PSTN reach.

SIP Over WebSocket: How Browser Calling Works Without an App

In short

SIP over WebSocket means carrying SIP call signaling inside a WebSocket connection (the SIP WSS transport) so a web browser can place and receive calls without any plugin or softphone. StartACall uses this same browser native stack, so you make outbound calls in Chrome, Safari, Edge, or Firefox with no app download, no SIM, and no phone number, billed per minute.

What SIP over WebSocket actually does

SIP (Session Initiation Protocol) sets up, manages, and tears down calls. Traditionally it travels over UDP or TCP, which browsers cannot open directly. SIP over WebSocket wraps those same SIP messages inside a WebSocket, normally the secure WSS variant on port 443, so the signaling rides the same encrypted channel a website already uses. The browser then negotiates the actual audio with WebRTC.

In short, WebSocket handles the call setup messages and WebRTC handles the live voice. Together they let a plain tab register, dial, and ring with no installed software. This is exactly why a service can offer calling from a URL instead of a download.

How StartACall puts it to work

StartACall is built on this browser native model, so you never touch SIP configuration yourself. You open the site, and the page handles the signaling and media for you. Outbound calls need no phone number and are pay as you go, billed per minute, which suits international and ad hoc calling.

If you also want to receive calls, you add a US or Canada digital number for as little as $2.14 a month and at most about $5, and inbound calls ring straight in your browser. All voice is end to end encrypted, which matters for business and privacy focused calling.

Frequently asked questions

Is SIP over WebSocket the same as WebRTC?+

No. They work together. SIP over WebSocket carries the call control and signaling messages, while WebRTC carries the encrypted audio. A browser dialer typically uses both at once.

Do I need to set up a SIP client or softphone to use StartACall?+

No. StartACall runs entirely in the browser. There is no softphone to install, no SIP credentials to enter, and no SIM card. You just open the site in Chrome, Safari, Edge, or Firefox and call.

Why use WebSocket instead of regular SIP ports?+

Browsers cannot open raw UDP or TCP SIP sockets for security reasons. WebSocket, especially the WSS form on port 443, passes cleanly through firewalls and proxies, so calling works on networks that block traditional SIP.

Are calls encrypted?+

Yes. StartACall calls are end to end encrypted, and the WSS signaling layer is secured as well, which makes the setup well suited for business and privacy sensitive calls.

Last reviewed June 2026Reviewed by the StartACall calling teamDialing rules cross checked against ITU international dialing procedures
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