"WebRTC Native Stack is considered as a signal chain as close to the Hardware Abstraction Layer (HAL) as possible."

Getting Started

This repository involves a Step by Step Gide to perform WebRTC STUN, TURN Communication in the real world. This Guide is based on the referenced article which is basically a complete understanding of WebRTC in the real world: STUN, TURN and signaling for Web Browsers.

If you want to do communication using WebRTC in Android, then Good luck guys! There is no need to beating around the bush (Redundant Information About WebRTC on Internet (Mostly For Web Browsers)). Just calm down and read this article. You will end up with a realtime communication over TURN and STUN using WebRTC.

For Compilation and Building the WebRTC Library for Android, you should have to look into this refernce:

Compile_WebRTC_Library_For_Android

For real-time Communication and AudioProcessing in Android, I will recommend you to must visit these refernces:

Quick Introduction

WebRTC applications need to do several things like:

Get streaming audio, video or other data.
Get network information such as IP addresses and ports, and exchange this with other WebRTC clients (known as peers) to enable connection, even through NATs and firewalls.
Coordinate signaling communication to report errors and initiate or close sessions.
Exchange information about media and client capability, such as resolution and codecs.
Communicate streaming audio, video or data.

WebRTC implemented open standards for real-time, plugin-free video, audio and data communication. WebRTC is used in various apps like WhatsApp, Facebook Messenger, appear.in and platforms such as TokBox. To acquire and communicate streaming data, WebRTC implements three APIs:

MediaStream
PeerConnection
DataChannel

All three APIs are supported on mobile and desktop by Chrome, Safari, Firefox, Edge and Opera. You can get the complete documentation and details of these three APIs in these references:

All of the above three documentations belong to Web-browsers only. But here, we will discuss for Android.

Signaling

The most important thing to remember is that "Signaling is not the part of WebRTC! Why? Because of these few reasons such as;

To avoid redundancy, and
To maximize compatibility with established technologies.

The exchange of information via signaling must have completed successfully before peer-to-peer streaming can begin. Signaling is used to exchange three types of information:

Session control messages: to initialize or close communication and report errors.
Network configuration: to the outside world, what's my computer's IP address and port?
Media capabilities: what codecs and resolutions can be handled by my browser and the browser it wants to communicate with?

Signaling methods and protocols are not specified by WebRTC standards. On the other hand, Signaling is the process of coordinating communication. In order for a android application to;

Set up a 'call' {Voice, Video},
Share media files i.e. (Voice Notes, Documents etc)

Android clients (related terminologies {terminals, nodes, members}) need to exchange information such as:

1. Session control messages used to open or close communication.

SDP interface describes one end of a connection—or potential connection—and how it's configured. It involves a JSON object with multiple two values (sdp, type)

{
sdp : "v=0 o=- 3709108758280432862 2 IN IP4 127.0.0.1 s=- t=0 0 a=msid-semantic: WMS m=application 9 DTLS/SCTP 5000 c=IN IP4 0.0.0.0 a=ice-ufrag:/MM7lfHOlMNfSMRk a=ice-pwd:EogZo3Zihb1g0XWgYFKHpeTk a=fingerprint:sha-256 BE:69:CE:D2:D6:41:41:DB:93:3E:3C:F5:D5:3D:D2:5A:33:8A:B0:A6:47:08:AE:24:A0:F6:FE:8F:39:65:21:CE a=setup:actpass a=mid:data a=sctpmap:5000 webrtc-datachannel 1024 ",

type : "offer"
}

You can get more information about SDP (Session Description Protocol).

The property SessionDescription.type is a read-only value of type SdpType which describes the description's type. The possible values are defined by an enum of type SdpType are as follows.

"offer", the description is the initial proposal in an offer/answer exchange.
"answer", the description is the definitive choice in an offer/answer exchange.
"pranswer", the description is a provisional answer and may be changed when the definitive choice will be given.
"rollback", the description rolls back to offer/answer state to the last stable state.

Here is very specific and detailed intuition about SdpType (Session Description Type).

2. Error messages and Callbacks.

3. Media metadata such as codecs and codec settings, bandwidth and media types.

4. Key data, used to establish secure connections.

5. Share ICECandidates with each other which is Network data, such as a host's IP address and port as seen by the outside world.

It involves a JSON object with 4 values (candidate, sdpMid, sdpMLineIndex, type):

{
 candidate:"candidate:5720275078 1 udp 8837102613 9201:398:am9u:14uf:2934:r39a:h753:z43i 38842 typ host generation 3 ufrag uEJl network-id 3 network-cost 82",
 sdpMid:"audio",
 sdpMLineIndex:2,
 type:"candidate"
}

IceCandidate Interface represents a candidate ICE (Internet Connectivity Establishment) configuration which may be used to establish an PeerConnection between Android Phones.

This signaling process needs a way for clients to pass messages back and forth. That mechanism is not implemented by the WebRTC APIs: You need to build it yourself. I will describe below some ways to build a signaling service. However, a little context is, you can follow these references to implement signaling:

STUN vs TURN

STUN (Session Traversal Utilities for NAT) is a standardized set of methods, including a network protocol, for traversal of network address translator gateways in applications of real-time voice, video, messaging, and other interactive communications. TURN (Traversal Using Relay NAT) is a protocol that allows a client to obtain IP addresses and ports from such a relay.

While Communicating with Android Peers, there are mostly two alternate data paths are shown, although only one data pathway will be active in a connection. This is because the Data (Audio, Video, Messages, Fax etc) Pathway can be

Either a direct connection (92% of connection attempts can take place directly) or
Through a relay server (8% of connection attempts require an intermediary relay server).

A third data pathway, not shown, is a direct connection from computer to computer when there is no intermediary firewall. The following diagram shows these two pathways.

Now obviously, while doing such a stuff, it turns out that you will be confused with a question such as STUN or TURN which one to refer and Why? You can use open source as well as paid STUN & TURN Services such as:

Request and Response Architecture of STUN/TURN Services:

A REST API to Access the TURN Services basically involves the following steps such as:

Request:

The request includes the following parameters, specified in the URL:

service: specifies the desired service (turn)
username: an optional user id to be associated with the
credentials
key: if an API key is used for authentication, the API key

Example:

     GET /?service=turn&username=mbzrxpgjys

Response:

The response is returned with content-type "application/json", and consists of a JSON object with the following parameters:

username
password
ttl
uris

Example:

   {
     "username" : "12334939:mbzrxpgjys",
     "password" : "adfsaflsjfldssia",
     "ttl" : 86400,
     "uris" : [
       "turn:1.2.3.4:9991?transport=udp",
       "turn:1.2.3.4:9992?transport=tcp",
       "turns:1.2.3.4:443?transport=tcp"
     ]
    }

WebRTC Interactions:

The returned JSON is parsed into an IceServer object, and supplied as part to use when creating a PeerConnection as follows:

         List<PeerConnection.IceServer> iceServers = new LinkedList<>();
                for (int i = 0; i < example.iceServers.size(); i++) {
                    if (!example.iceServers.get(i).username.isEmpty())
                        iceServers.add(new PeerConnection.IceServer(example.iceServers.get(i).url, example.iceServers.get(i).username, example.iceServers.get(i).credential));
                    else
                        iceServers.add(new PeerConnection.IceServer(example.iceServers.get(i).url));
                }

        constraints = new MediaConstraints();
        peerConnection = peerConnectionFactory.createPeerConnection(iceServers, constraints, peerConnectionObserver);

You can get the more details about the in draft i.e A REST API For Access To TURN Services draft-uberti-behave-turn-rest-00. In general, WebRTC needs servers to fulfill four types of server-side functionality such as:

User discovery and communication
Signaling
NAT/firewall traversal
Relay servers in case peer-to-peer communication fails

Peer to Peer Communication

Here we will discuss the complete workaround to establish Peer-to-Peer communication between two Android Phones/Terminal/Nodes which basiclly depend on these modules:

Exchange Media Configuration Information
Exchange Network Configuration Information
Communication Via DataChannel

I will start explaining the following Process in very specific detail. So first look at the following entire exchange of information between Two Peers:

Basic Terminologies:

Peer-A <--> Caller <--> Steve Jobs (Steve) The Person who initiate PeerConnection
Peer-A <--> Callee <--> Bill Gates (Bill) The Person who accepts PeerConnection

PeerConnection is the API used by the WebRTC Android Application to create connection between peers and communicate audio and video. PeerConnection has two tasks to initialize the Process such as:

Ascertain (make sure) the local media conditions such as bandwidth, media types, resolution & codec capabilities (opus, speex etc).
Start Gathering the list of potential network addresses for the application's host, known as IceCandidates.

This metadata is used for the offer and answer mechanism. Once this local data has been ascertained (Gathered), it must be exchanged via a signaling mechanism with the remote peer.

Exchange Media Configuration Information

Now I will discuss complete Offer/Answer mechanism with all its glory details:

1. Steve creates a PeerConnection Object.

        peerConnection = peerConnectionFactory.createPeerConnection(iceServers, constraints, peerConnectionObserver);

2. Steve creates an offer (an SDP session description) with the PeerConnection createOffer() method.

        peerConnection.createOffer(sdpObserver, constraints);

3. Steve calls setLocalDescription() with his offer.

        peerConnection.setLocalDescription(sdpObserver, sessionDescription);

4. Steve makes a json object for (jsonify) the offer and uses a signaling mechanism to send it to Bill.

5. Bill calls setRemoteDescription() with Steve's offer, so that his PeerConnection knows about Steve's setup for audio or video communication.

        peerConnection.setRemoteDescription(sdpObserver, sdp2);

6. Bill then calls the createAnswer() method, and the success callback for this is passed a local session description: Bill's answer as follows

        peerConnection.createAnswer(sdpObserver, constraints);

7. Bill sets her answer as the local description by calling setLocalDescription().

        peerConnection.setLocalDescription(sdpObserver, sessionDescription);

8. Bill then uses the signaling mechanism to send his json object of the (jsonify) answer back to Steve.

{
sdp : "v=0 o=- 3709108758280432862 2 IN IP4 127.0.0.1 s=- t=0 0 a=msid-semantic: WMS m=application 9 DTLS/SCTP 5000 c=IN IP4 0.0.0.0 a=ice-ufrag:/MM7lfHOlMNfSMRk a=ice-pwd:EogZo3Zihb1g0XWgYFKHpeTk a=fingerprint:sha-256 BE:69:CE:D2:D6:41:41:DB:93:3E:3C:F5:D5:3D:D2:5A:33:8A:B0:A6:47:08:AE:24:A0:F6:FE:8F:39:65:21:CE a=setup:actpass a=mid:data a=sctpmap:5000 webrtc-datachannel 1024 ",

type : "answer"
}

9. Steve then sets Bill's answer as the remote session description using setRemoteDescription().

        peerConnection.setRemoteDescription(sdpObserver, sdp2);

Exchange Network Configuration Information

In the portion, Each of pair start 'Gathering or finding candidates' which refers to the process of finding network interfaces and ports using the Ice FrameWork.

1. Steve creates an PeerConnection object with an onicecandidate(IceCandidate iceCandidate) handler.

        @Override
        public void onIceCandidate(IceCandidate iceCandidate) {
            if (username.equals("Steve")) {
                IceCandidateModel iceCandidateModel = new IceCandidateModel("candidate", iceCandidate.sdpMLineIndex, iceCandidate.sdpMid, iceCandidate.sdp);
                Log.e(TAG, "STEVE's ICE CANDIDATE: " + iceCandidateModel.candidate + " " + iceCandidateModel.sdpMid + " " + iceCandidateModel.type + " " + iceCandidateModel.sdpMLineIndex);
                // Do some signaling Stuff
            } else if (username.equals("Bill")) {
                IceCandidateModel iceCandidateModel = new IceCandidateModel("candidate", iceCandidate.sdpMLineIndex, iceCandidate.sdpMid, iceCandidate.sdp);
                Log.e(TAG, "BILL's ICE CANDIDATE: " + iceCandidateModel.candidate + " " + iceCandidateModel.sdpMid + " " + iceCandidateModel.type + " " + iceCandidateModel.sdpMLineIndex);
                // Do some signaling Stuff
            }

2. The handler is run when network candidates become available.

3. Steve sends serialized candidate data (json object) to Bill, via whatever signaling channel they are using: TCPSocket, Firebase or some other mechanism.

4. When Bill gets a candidate message from Steve, he calls addIceCandidate() method, to add the candidate to the remote peer description.

        IceCandidate iceCandidate = new IceCandidate(iceCandidateModel.sdpMid, iceCandidateModel.sdpMLineIndex, iceCandidateModel.candidate);
        peerConnection.addIceCandidate(iceCandidate);

Summary

To sum up the above discussion, We have a Android Client also known as Steve first create an offer using PeerConnection createOffer() method. The return from this is passed an SessionDescription: Steve's local session description. In the callback, Steve sets the local description using setLocalDescription() and then sends this session description to Bill via their signaling channel. Note that PeerConnection won't start gathering candidates until setLocalDescription() is called. Bill sets the description which Steve sent him as the remote description using setRemoteDescription(). Bill runs the PeerConnection createAnswer() method, passing it the remote description he got from Steve, so a local session can be generated that is compatible with him. The createAnswer() callback is passed an SessionDescription: Bill sets that as the local description and sends it to Steve. When Steve gets Bill's session description, he sets that as the remote description with setRemoteDescription. Its a very simple and pretty straight forward discussion: Bravo!!!

Communication Via DataChannel

Once the PeerConnection is established between the Peer-A and Peer-B, they both can use DataChannel API to share Data between each other. The DataChannel API enables peer-to-peer exchange of arbitrary data (audio, video, etc), with low latency and high throughput. Steve sends its useful information in the form of bytes using DataChannel send(new DataChannel.Buffer(buffer, false)).

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        ByteBuffer buffer = ByteBuffer.wrap(audio.getRecordedData());
                        dataChannel.send(new DataChannel.Buffer(buffer, false));
                    }
                }
            }).start();

On the other side, Bill receives, steve information using DataChannel buffer.data.get(data) method.

        @Override
        public void onMessage(final DataChannel.Buffer buffer) {
            try {

                if (!buffer.binary) {
                    int limit = buffer.data.limit();
                    byte[] data = new byte[limit];
                    buffer.data.get(data);
                    byteQueue.add(data);

                } else {
                    Log.e(TAG, "Data is not received.");

                }
            } catch (Exception e) {
                e.printStackTrace();
                Log.e(TAG, "ERROR: " + e.toString());
            }
        }

Communication occurs directly between Android Phones. DataChannel communication can be much faster than Simple Socket communication even if a relay (TURN) server is required when 'hole punching' to cope with firewalls and NATs fails.

There are many potential use cases for the API, including:

Gaming
Remote desktop applications
Real-time text chat
File transfer
Decentralized networks

The API has several features to make the most of RTCPeerConnection and enable powerful and flexible peer-to-peer communication:

Leveraging of RTCPeerConnection session setup.
Multiple simultaneous channels, with prioritization.
Reliable and unreliable delivery semantics.
Built-in security (DTLS) and congestion control.
Ability to use with or without audio or video.

Each P2P TransportChannel represents a data channel between the local and remote Android Terminals. This channel actually obscures a complex system designed for robustness and performance. P2P TransportChannel manages a number of different Connection objects, each of which is specialized for a different connection type (UDP, TCP, etc). A Connection object actually wraps a pair of objects:

A Port subclass, representing the local connection; and
An address representing the remote connection.

If a particular connection fails, P2P TransportChannel will seamlessly switch to the next best connection. The following diagram shows a high level view of the data pathway inside the Peer to Peer Component.

Conclusion

The WebRTC APIs and standards can very useful and optimized tools for content creation and communication—for real-time audio, gaming, video production, music making, news gathering and many other applications. I have tried my best to give you guys the more appropriate and detailed information with the simple implementation. All you need is to create and Android Application and inside the application build.gradle file just includes the following dependency:

        implementation 'io.pristine:libjingle:11139@aar'

As libjingle (Build on the top of WebRTC Native Stack) has implemented all of the three above mentioned WebRTC APIs in a very detailed and specific way to follow the standards of WebRTC. To get the detailed intuition about libjingle you can visit Google Talk for Developers. Good Luck Guys!!!

mail2chromium/Android_Realtime_Communication_Using_WebRTC

"WebRTC Native Stack is considered as a signal chain as close to the Hardware Abstraction Layer (HAL) as possible."

Content of this Document

Summary