ICE Candidates and Connectivity
Explore ICE candidates, how they represent network addresses, and how ICE facilitates finding the best path for peer-to-peer connection.
ICE Candidates and Connectivity is a free Real-Time Streaming Systems (WebRTC + Live Data) lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Real-Time Streaming Systems (WebRTC + Live Data) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
ICE: The Connectivity Finder
ICE stands for Interactive Connectivity Establishment. It's a crucial framework in WebRTC that helps establish direct connections between peers, even when they are behind tricky networks like NATs or firewalls.
Think of ICE as a smart detective. It finds all possible routes for two people to talk directly and then picks the best one.
Overcoming Network Barriers
Many devices connect to the internet through routers that use NAT (Network Address Translation) or have firewalls. These act like security guards, often blocking direct incoming connections.
- NAT: Hides private network IPs behind a single public IP.
- Firewalls: Block unauthorized access.
Without ICE, establishing a direct peer-to-peer connection in such environments would be nearly impossible.
What Are ICE Candidates?
An ICE Candidate is essentially a potential network address and port where a peer can be reached. Each peer collects multiple candidates representing different ways it can communicate.
These candidates are like different phone numbers or addresses you might have: your home number, your work number, a friend's number where you can be reached, etc. ICE tries them all.
Types of ICE Candidates
There are three main types of ICE candidates:
- Host Candidates: These are the peer's actual local IP addresses. They work best for direct connections within the same local network.
- Server Reflexive Candidates: Obtained from a STUN server. This is your public IP address and port as seen by an external server, helping peers behind NATs find each other.
- Relayed Candidates: Obtained from a TURN server. If direct connection isn't possible, a TURN server relays all traffic. This is the last resort.
Gathering Candidates: The Process
When a WebRTC connection is initiated, each peer's browser (the WebRTC agent) starts collecting ICE candidates. It actively queries the local network, STUN servers, and potentially TURN servers to find all possible communication paths.
This collection process happens continuously in the background as the RTCPeerConnection is being set up.
Code: Listening for Candidates
In JavaScript, you listen for icecandidate events on your RTCPeerConnection object to get these candidates. Each event provides a new candidate to share with the remote peer via your signaling server.
const pc = new RTCPeerConnection();
pc.onicecandidate = (event) => {
if (event.candidate) {
console.log("New ICE candidate found:");
console.log(event.candidate.candidate);
// Send this candidate to the remote peer via signaling server
} else {
console.log("ICE candidate gathering complete.");
}
};
console.log("Listening for ICE candidates...");
// Note: This snippet requires a full browser WebRTC context to run
// and produce actual candidates. It's for demonstration.Exchanging Candidates: Signaling
Once candidates are gathered, they must be exchanged between the two peers. This happens through your signaling server, the same server used to exchange SDP offers and answers.
- Each peer sends its collected candidates to the signaling server.
- The signaling server forwards these candidates to the other peer.
This process is often called "trickle ICE" because candidates are sent as they are found, rather than waiting for all of them.
The Connectivity Check
After exchanging candidates, ICE begins its connectivity checks. Both peers try to establish connections using every possible pair of local and remote candidates. This involves sending small "STUN binding requests" to test reachability.
ICE then prioritizes and selects the most efficient and reliable path. It prefers direct host connections, then STUN-relayed public IPs, and finally TURN-relayed connections.
Quick Check: ICE Candidate Types
Which type of ICE candidate is obtained with the help of a STUN server to reveal a peer's public IP address?
Recap: ICE in Action
In this lesson, you learned about ICE Candidates and how they enable WebRTC to establish peer-to-peer connections across diverse networks.
- ICE candidates are potential network addresses.
- They come in types: Host, Server Reflexive (STUN), and Relayed (TURN).
- Peers gather and exchange these candidates via a signaling server.
- ICE then performs connectivity checks to find the best possible path for direct communication.
ICE is the unsung hero ensuring your real-time calls find a way through the internet's complexities!
Frequently asked questions
Is the “ICE Candidates and Connectivity” lesson free?
Yes — the full text of “ICE Candidates and Connectivity” is free to read here on the web, and the Real-Time Streaming Systems (WebRTC + Live Data) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Real-Time Streaming Systems (WebRTC + Live Data) course, upgrade to CoddyKit PRO.
What will I learn in “ICE Candidates and Connectivity”?
Explore ICE candidates, how they represent network addresses, and how ICE facilitates finding the best path for peer-to-peer connection. You practise Real-Time Streaming Systems (WebRTC + Live Data) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Real-Time Streaming Systems (WebRTC + Live Data)?
No prior experience is required. Real-Time Streaming Systems (WebRTC + Live Data) on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “ICE Candidates and Connectivity” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Real-Time Streaming Systems (WebRTC + Live Data) lesson?
Yes. Every Real-Time Streaming Systems (WebRTC + Live Data) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- The Role of Signaling Servers
- SDP: Session Description Protocol
- ICE Candidates and Connectivity
- Renegotiation and Connection State