• What is WebRTC ?
• Media Stack in Browser
• Standardization by IETF and W3C
• Open and Free Codecs
• Independant of Signalling 
• NAT-traversal ( ICE, STUN, and TURN)
• Why is WebRTC so important ?
• Peer to peer Communication
  • Two party call p2p
  • Multiparty Call and mesh network
• Browser Adoption
• webrtc-apis
• WebRTC CPaaS Solutions
  1. Pluggable module or npm
  2. collaboration as a Service ie CaaS
  3. Communication Platform

WebRTC 1.0: Real-time Communication Between Browsers – W3C Candidate Recommendation 13 December 2019 https://www.w3.org/TR/webrtc/

webrtcdevelopment Open Source WebRTC SDK and its implementation steps https://github.com/altanai/webrtc

Read more in the layers of webrtc  and their functionalities here :  WebRTC layers

What is WebRTC ?

WebRTC (Web Real-Time Communication) is an API definition drafted by the World Wide Web Consortium (W3C) that supports browser-to-browser applications for voice calling, video chat, and P2P file sharing without the need for either internal or external plugins.

• Enables browser to browser media streaming over secure RTP profile
• Standardization, on an API level at the W3C and at the protocol level at the IETF.
• Enables web browsers with Real-Time Communications (RTC) capabilities
• written in c++ and javascript
• BSD style license
• free, open project available in all major browsers 

Media Stack in Browser

The following is the browser side stack for webrtc media .  

Voice Engine

• iSAC: wideband and super wideband audio codec for streaming audio
• iLBC: narrowband speech codec for streaming audio
• Opus: constant and variable bitrate encoding 
• NetEQ: Net Equalizer
• Dynamic jitter buffer + error concealment algorithm
• Acoustic Echo Canceler (AEC) : remove acoustic echo
• Noise Reduction (NR) : remove background noise

Video engine

• VideoEngine is a framework video media chain for video, from camera to the network, and from network to the screen.
• VP8 : Video codec from the WebM Project. Designed for low latency Real time Comm. 
• Video Jitter Buffer: conceal the effects of jitter and packet loss on overall video quality.
• Image enhancements : removes video noise 

Transport

• Transport / Session Layer of WebRTC stack provide Session Management for WebRTC media streams .
• It consists of network stack for Secure RTP, the Real Time Protocol.
• STUN/ICE for NAT , Network Address Traversal across various types of networks.
• Session Management which is an abstracted session layer for call setup.

Standardization by IETF and W3C

As of the 2019 update the W3C defines it as

a set of ECMAScript APIs in WebIDL to allow media to be sent to and received from another browser or device implementing the appropriate set of real-time protocols. The specification being developed in conjunction with a protocol specification developed by the IETF RTCWEB group and an API specification to get access to local media devices.

W3C contribution to WebRTC standardization

• Media Stream Functions : API for connecting processing functions to media devices and network connections, including media manipulation functions.

• Audio Stream Functions : An extension of the Media Stream Functions to process audio streams (e.g. automatic gain control, mute functions and echo cancellation).

• Video Stream Functions : An extension of the Media Stream Functions to process video streams (e.g. bandwidth limiting, image manipulation or “video mute“).

• Functional Component : API to query presence of WebRTC components in an implementation, instantiate them and connect them to media streams.

• P2P Connection Functions : API functions to support establishing signalling protocol-agnostic peer-to-peer connections between Web browsers

• API specification Availability

WebRTC 1.0: Real-time Communication Between Browsers –  Draft 3 June 2013 available

• Implementation Library: WebRTC Native APIs

Media Capture and Streams – Draft 16 May 2013

• Supported by Chrome , Firefox, Opera in desktop of all OS ( Linux, Windows , Mac )
• Supported by Chrome , Firefox  in Mobile browsers ( android )

IETF contribution to to WebRTC standardization

• Communication model
• Security model
• Firewall and NAT traversal
• Media functions
• Functionality such as media codecs, security algorithms, etc.,
• Media formats
• Transport of non media data between clients
• Input to W3C for APIs development
• Interworking with legacy VoIP equipment

Open and Free Codecs

Codecs signifies the media stream’s compession and decompression. For peers to have suceesfull excchange of media, they need a common set of codecs to agree upon for the session . The list codecs are sent  between each other as part of offeer and answer or SDP in SIP.

WebRTC uses bare MediaStreamTrack objects for each track being shared from one peer to another. Codecs associated in those tracks is not mandated by webrtc soecification.

For video as per RFC 7742 WebRTC Video Processing and Codec Requirements , the manadatory codesc to be supported by webrtc clients are : VP8 and H.264‘s Constrained Baseline profile.

For Audio as per RFC 7874 WebRTC Audio Codec and Processing Requirements, browser must support Opus codec as well as G.711‘s PCMA and PCMU formats.

Video Resolution handling

Unless the SDP specifically signals otherwise, the web browser receiving a WebRTC video stream must be able to handle video at at least 20 FPS at a minimum resolution of 320 pixels wide by 240 pixels tall.

In the best scenarios ( avaible bandwidth and media devices ) VP8 had no upper mark set on resolution of vdieo stream hence the stream can even go asfar as  maximum resolution of 16384×16384 pixels.

Independant of Signalling 

Webrtc does not specify any signalling / telecommunication protocl and it is upto the adoptor to perform ofeer/answer exchaneg in any way deemed fit for the usecase . For ex maple for a web only application on may use only plain websockets, whereas for a teelcom endpoints compatible app one should SIP as the protocol. 

NAT-traversal ( ICE, STUN, and TURN)

The post describe ICE  (Interactive Connectivity Establishment )  framework which is  mandatory by WebRTC standards.  It is find network interfaces and ports in Offer / Answer Model to exchange network based information with participating communication clients. ICE makes use of the Session Traversal Utilities for NAT (STUN) protocol and its extension, Traversal Using Relay NAT (TURN). I have written in detail about TURN based WebRTC flow diagrams in post below.

Learn about hosting / integrating different TURN servers for WebRTC in the article on “TURN server for WebRTC – RFC5766-TURN-Server , Coturn , Xirsys “.

Why is WebRTC so importatnt ?

The major players behind the conception and advancement of WebRTC standards and libraries are IETF, W3C, Java community, GSMA. The idea is to develop a Lightweight browser-based call console, to make SIP calls from a Web page. This was successfully achieved using fundamental technologies – Javascript, html5, web-sockets and TCP /UDP, open-source sip server. It is good to note that there is no extra extension, plugin or gateway required, such as flash support. Also, it bears cross-platform support, including Mozilla, chrome so on.

Bottlnecks

Although WebRTC is a great technology and holds very good potential it is not devoid of problems

(-) Secure networks and Firewalls block RTP
(-) Security in VPN and topology hiding
(-) Cross-platform concerns and codecs incompatible
(-) Late adopters like Microsoft and Apple

 Peer to peer Communication

 WebRTC forms a p2p communication channel between all the peers . that means as the participant count grows  , it converts to  a mesh networking topology with incoming and outgoing stream towards direction of each of its peers .

Two party call p2p

Peer to peer calling

Multiparty Call and mesh network

Mesh based arrangement .

 In special case of broadcasting or  large number of viewers ( without outgoing media stream ) it is recommended to setup a Media Control Unit ( MCU) which will replay the incoming stream to large number of users without putting traffic load on the clients from where the stream is actually originating .   Important note :    

1. It should be noted that these diagrams do not depict the ICE and NAT traversal and have been simplified for better understanding. In real-world scenarios, almost all the time STUN and TURN servers are involved. 
2. Also, the webrtc mandates the use of secure origin ( HTTPS ) on the webpage which invoke getusermedia to capture user media devices like audio, video and location.

Browser Adoption

As of March 2020 , webrtc is supported on following client’s browsers

• Desktop PC
  Microsoft Edge 12+[25]
  Google Chrome 28+
  Mozilla Firefox 22+[26]
  Safari 11+[27]
  Opera 18+[28]
  Vivaldi 1.9+
• Android
  Google Chrome 28+ (enabled by default since 29)
  Mozilla Firefox 24+[29]
  Opera Mobile 12+
• Chrome OS
• Firefox OS
• BlackBerry 10
• iOS
  MobileSafari/WebKit (iOS 11+)
• Tizen 3.0

Furthermore, read about the Steps for building and deploying WebRTC solution.

WebRTC APIs are the Javascript functions to access and process the browser media stack.

getUserMedia

acquires the audio and video media (e.g., by accessing a device’s camera and microphone)

Properties

ondevicechange

Methods

enumerateDevices()
getDisplayMedia()
getSupportedConstraints()
getUserMedia()

navigator.mediaDevices.getUserMedia({ audio: true, video: true })
.then(function(stream) {
  var video = document.querySelector('video');
  // Older browsers may not have srcObject
  if ("srcObject" in video) {
    video.srcObject = stream;
  } else {
    // Avoid using this in new browsers, as it is going away.
    video.src = window.URL.createObjectURL(stream);
  }
  video.onloadedmetadata = function(e) {
    video.play();
  };
})
.catch(function(err) {
  console.log(err.name + ": " + err.message);
});

DOMException Error on getusermedia

Rejections of the returned promise are made by passing a DOMException error object to the promise’s failure handler. Possible errors are:

AbortError : Although the user and operating system both granted access to the hardware device, problem occurred which prevented the device from being used.

NotAllowedError : One or more of the requested source devices cannot be used at this time. This will happen if the browsing context is insecure( http instead of https) or if the user has specified that the current browsing instance /sessionis not permitted access to the device or has denied all access to user media devices globally.

NotFoundError : No media tracks of the type specified were found that satisfy the given constraints.

NotReadableError : Although the user granted permission to use the matching devices, a hardware error occurred at the operating system, browser, or Web page level which prevented access to the device.

OverconstrainedError : no candidate devices which met the criteria requested. String value is the name of a constraint which was not meet, and a message property containing a human-readable string explaining the problem. Exmaple conatraints :

var constraints = { video: { facingMode: (front? "user" : "environment") } };

SecurityError : User media support is disabled on the Document on which getUserMedia() was called.

TypeError : The list of constraints specified is empty, or has all constraints set to false.

Pan/Tilt/Zoom camera controls

RTCPeerConnection

enables audio and video communication between peers. It performs signal processing, codec handling, peer-to-peer communication, security, and bandwidth management.

Properties

Methods

RTC Signalling states

• stable : There is no offer/answer exchange in progress. This is also the initial state, in which case the local and remote descriptions are empty.
• have-local-offer : Local description, of type “offer”, has been successfully applied.
• have-remote-offer : Remote description, of type “offer”, has been successfully applied.
• have-local-pranswer : Remote description of type “offer” has been successfully applied and a local description of type “pranswer” has been successfully applied.
• have-remote-pranswer : Local description of type “offer” has been successfully applied and a remote description of type “pranswer” has been successfully applied.
  closed The RTCPeerConnection has been closed; its [[IsClosed]] slot is true.

RTCSDPType

• offer : SDP offer.
• pranswer : RTCSdpType of pranswer indicates that a description MUST be treated as an [SDP] answer, but not a final answer.
• answer : treated as an [SDP] final answer, and the offer-answer exchange MUST be considered complete. A description used as an SDP answer may be applied as a response to an SDP offer or as an update to a previously sent SDP pranswer.
• rollback : canceling the current SDP negotiation and moving the SDP [SDP] offer back to what it was in the previous stable state.

RTCPeerConfiguration

Defines a set of parameters to configure how the peer-to-peer communication established via RTCPeerConnection

iceServers of type sequence : array of objects describing servers available to be used by ICE, such as STUN and TURN servers.

iceTransportPolicy of type RTCIceTransportPolicy : bundle policy affects which media tracks are negotiated if the remote endpoint is not bundle-aware, and what ICE candidates are gathered. If the remote endpoint is bundle-aware, all media tracks and data channels are bundled onto the same transport.

• relay : ICE Agent uses only media relay candidates such as candidates passing through a TURN server.
• all : The ICE Agent can use any type of candidate when this value is specified.

bundlePolicy of type RTCBundlePolicy.
media-bundling policy to use when gathering ICE candidates. Types :

• balanced : Gather ICE candidates for each media type in use (audio, video, and data). If the remote endpoint is not bundle-aware, negotiate only one audio and video track on separate transports.
• max-compat : Gather ICE candidates for each track. If the remote endpoint is not bundle-aware, negotiate all media tracks on separate transports.
• max-bundle : Gather ICE candidates for only one track. If the remote endpoint is not bundle-aware, negotiate only one media track.

rtcpMuxPolicy of type RTCRtcpMuxPolicy.
rtcp-mux policy to use when gathering ICE candidates.

certificates of type sequence
A set of certificates that the RTCPeerConnection uses to authenticate.

iceCandidatePoolSize of type octet, defaulting to 0
Size of the prefetched ICE pool as defined in [JSEP]

RTCDataChannel

Allows bidirectional communication of arbitrary data between peers. It uses the same API as WebSockets and has very low latency.

• (+) DataChannel is p2p and is also ened to end encrypted leader to higher privacy
• (+) build in security due to p2p transfer
• (+) high throughput than text transfer via a messaging server
• (+) lower latency as p2p transfer takes shortest route

getStats

allows the web application to retrieve a set of statistics about WebRTC sessions. These statistics data are being described in a separate W3C document.

Call Setup betweeb WebRTC Endpoints

WebRTC CPaaS Solutions

Basics for building a WebRTC based communication solution :-

• Websockets for signalling / Offer Answer
• TURN server like xirsys(paid), CoTURN(opensource , self hosted)
• Js library for WebRTC wrappers
• Https served webpage
• WebRTC enabled Browser

Approaches to develop webrtc unified communication system

1. Pluggable module or npm

Source code for the WebRTC project is shipped as a pluggable library or npm module.

2. collaboration as a Service ie CaaS

Clients redirect users to our WebRTC platform for communication.

3. Communication Platform

We provider all communication and related Services as a standalone platform

Updates in W3C 13 Dec , 2019

Over the years since its adoption many of the associated tech were depricated from the Webrtc based platforms and enviornments , some of which are: OAuth as a credential method for ICE servers
Negotiated RTCRtcpMuxPolicy (previously marked at risk)
voiceActivityDetection
RTCCertificate.getSupportedAlgorithms()
RTCRtpEncodingParameters: ptime, maxFrameRate, codecPayloadType, dtx, degradationPreference
RTCRtpDecodingParameters: encodings
RTCDatachannel.priority

Some of the newly added features include:

restartIce() method added to RTCPeerConnection
Introduced the concept of “perfect negotiation”, with an example to solve signalling races.
Implicit rollback in setRemoteDescription to solve races.
Implicit offer/answer creation in setLocalDescription to solve races.

References :

• [1] WebRTC 1.0: Real-time Communication Between Browsers – W3C Candidate Recommendation 13 December 2019 https://www.w3.org/TR/webrtc/
• [2] Google groups discuss-webrtc https://groups.google.com/g/discuss-webrtc
• [3] Linkedin group on webrtc Development https://www.linkedin.com/groups/6545894/