This session focus on Introduction to WebRTC, describes SDP and also specify how to implement signalling & handling NAT traversal using TURN & STUN.

1. WebRTC
Introduction
& Basics

2. WebRTC
 WebRTC is FOSS that provides browsers and mobile applications with Real Time Communication
capabilities via simple API’s
 It is supported by almost all modern browsers
 Mobile applications & desktop applications can also embed WebRTC without much hassle
 It leverages multiple protocols and standards like
 TURN/STUN(Traversal Using Relay NAT/Session Traversal Utilities for NAT)
 ICE(Interactive Connectivity Establishment)
 SIP(Session Initiation Protocol)
 SDP(Session Description Protocol)
 It is a project supported by Google, Mozilla & Opera

3. WebRTC
 It can be used for low cost, high quality audio, video & data communication
 WebRTC itself is written in C++
 Available for android and iOS integration without any hassle
 RTCPeerConnection is the heart of WebRTC, handles lots of things including

4. Connection Process
 Caller creates an offer SDP using some constraints
 Send this SDP to the callee via some signaling mechanism
 Callee accepts the offer and generate an answer SDP
 Answer SDP is sent to caller using some signaling mechanism
 Meanwhile both caller and callee discovers ICE candidates and exchange them with each others
using signaling mechanism
 Both machines have 2 SDP’s, i.e. local and remote
 Both machines have ICE candidates from each other
 WeRTC connects both machines using ICE Candidates
 Connection is Peer-Peer.

5. Signaling Mechanism
 Signaling is required to transmit following from caller to callee and vice versa
 Session Description
 ICE Candidates
 It can use any protocol & messaging mechanism
 XMPP has an XEP for this called Jingle
 You can use WebSockets for this as well.
 WebRTC doesn’t restrict any protocol
 Signaling is lightweight, it doesn’t transmit voice, video or data, instead it only transmits SDP’s
and Candiates

6. Sample SDP
Microsoft
Word Document

7. Both
machines
are in same
network

8. NAT
 Network Address Translation is a process in which a device(usually firewall) assigns a public IP to a
computer or group of computers inside a private network.
 Main purpose of NAT is to limit the number of public IP addresses a network or organization
must use.
 Symmetric NAT also map a specific port network’s public IP, every time a new connection is made
a new port will be mapped.

9. NAT continued
 If systems are behind NAT then simply sending candidates doesn’t work
 If candidates are local IP addresses and ports and both machines resides on different private
networks then they won’t be able to connect.
 We somehow need to know the public IP of the caller and a port mapped to that public IP.
 Similarly we need to know the same information on second public

10. Both
machines
are behind
NAT

11. STUN
 STUN(Session Traversal Utilities for NAT) provides a set of tools for NAT traversal.
 It actually probes your public IP, bind a port on NAT machine to your local machine
 It requires a server for NAT traversal

12. NAT with
STUN

13. TURN
 Sometimes peer-peer connection fails because of some of the following reasons
 Firewalls blocking peer-peer connections because of custom ports
 NAT device not allowing ports binding
 State restrictions based on type of traffic
 TURN(Traversal Using Relay Network) provide a fallback mechanism if peer-peer connection fails
 It requires a Relay Server to act as a relay data among different machines
 Ensures that calling works in almost all of the environments

14. NAT with
TURN

15. ICE(Interactive Connectivity Establishment)
 ICE is basically a mechanism to find multiple paths to communicate
 It also provides costs of different paths so that all parties use optimal paths to communicate and
user experience is improved
 Intention is to find best route between caller and callee.
 It leverages STUN to find routes

16. Topologies
supported
One-One Call
Mesh: Small N-way call
Star: Medium N-way call
MCU(Multipoint Conferencing Unit):
N-way call

17. Questions?