Signaling In webRTC

In the perfect world webRTC enable peer to peer communication but in the real world webRTC still needs signaling servers. Here I’m going to explain you why we need signaling servers and where we need signaling servers.

What is Signaling?

Signaling is the exchange of information between involved points in the network that sets up, controls, and terminate each connections. its clients need to exchange some information such as

• ·         Session control information 

                Determines when to initialize, close, and modify communications sessions.

• ·         Network Data

                Callers can find callees endpoints.

• ·         Media Data

                is required to determine the codecs and media types that the callers and callees have in common.

So this signaling process needs a way for clients to pass messages back and forth.

Why signaling is not defined by webRTC APIs?

To avoid redundancy and to maximize compatibility with established technologies, signaling methods and protocols are not specified in webRTC standards.

Why we still need signaling servers in WebRTC?

In the perfect world signaling in webRTC is straight forward and simple. Every WebRTC endpoints would have a unique IP address that it could exchange with other peers in order to communicate directly. JSEP (JavaScript Session Establishment Protocol) gives a summary of this approach. But that document is lengthy and somewhat involved. Here is a simple and straightforward explanation that will provide you with enough information to be known.

The mechanism to establish a connection between two parties (Let’s say Alice and Bob).

1.      Alice creates an offer that contains his local SDP.

2.      Alice attaches that offer to something known as an RTCPeerConnection object.

3.      Alice sends his offer to the signaling server using WebSocket. WebSocket is a protocol that provides a full-duplex communications channel over a network connection. WebRTC standardized on WebSocket as the way to send information from a web browser to the signaling server and vice versa.

4.      Bob receives Alice’s offer using WebSocket.

5.      Bob creates an answer containing his local SDP.

6.      Bob attaches his answer, along with Alice’s offer, to Alice's own RTCPeerConnection object.

7.      Bob returns his answer to the signaling server using WebSocket.

8.      Alice receives Bobs’s offer using WebSocket.

Keeping it Simple

This should be enough for now to convey the following points.

·         WebRTC does not define signaling.

·         JSEP summarized signaling approach in webRTC.

·         A signaling server sits between two clients.

·         Clients use WebSocket to communicate to a signaling server and vice versa.