A presentation by Peter Dunkley (Technical Director, Crocodile RCS Ltd). Presentation date 14-May-2013.

1. WebRTC, TURN, and WebSocket
1

2. WebRTC, TURN, and WebSocket
WebRTC, TURN, and WebSocket
Peter Dunkley, Technical Director, Crocodile RCS Ltd
Email:
Twitter:
peter.dunkley@crocodile-rcs.com
@pdunkley

3. WebRTC is about media
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GetUserMedia Javascript API
–
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MediaStreams Javascript API
–
●
Provides access to microphones, web-cams, and
screen (for screen-sharing)
Routes streams between microphones/webcams/screens/speakers and network connections
PeerConnection Javascript API
–
Creates low-latency, secure connections between
peers
–
Streams may be audio, video, or data

4. Security and Quality of Service is built-in
●
New profile RTP/SAVPF
–
–
●
The S means DTLS is used – only the endpoints
can decode the stream
The F means RTCP feedback is used – enables
QoS in the endpoints
ICE is mandatory
–
STUN allows traversal of most NAT devices without
relays
–
TURN allows traversal of “badly behaved” NAT
devices

5. Mandatory To Implement (MTI) Codecs
●
Audio
–
–
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G.711
OPUS
Video
–
●
Big debate between H.264 and VP8
Connections and codecs are negotiated using
SDP

6. Media session interworking
●
●
Media Gateways or RTCWeb Breakers are
required for now
The RTP/SAVPF profile used by WebRTC:
–
Mandates security
–
Mandates quality of service
–
Mandates client-based NAT traversal
–
Contains network optimisations
–
Is not compatible with most deployed servers and
user-agents.

7. TURN Security
●
●
●
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TURN can use a lot of network bandwidth
This may be expensive for service providers so
security is needed to make sure it is not abused
Ordinary credentials stored in Javascript webapps can be easily read and are not safe
Google recently proposed a web-service API
for creating ephemeral credentials

8. Establishing media sessions requires signalling
Signalling
Server
Sig
nal
ling
Server
Browser
WebRTC media or DataChannel
Browser

9. Many signalling options
●
REST based
–
●
BOSH based
–
●
For example, PubNub, RestComm, Twilio
For example, some XMPP implementations
WebSocket based
–
For example, SIP or XMPP

10. What is WebSocket?
●
●
Safe, client-originated, connection to servers
Often used from web-browsers - but does not
have to be
●
It is an asynchronous protocol
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Traffic from the client is masked
●
●
Although carried over TCP WebSocket is a
frame based protocol
RFC 6455, “The WebSocket Protocol”

11. Why use SIP over WebSocket?
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SIP is the “Session Initiation Protocol”
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Requires less network infrastructure
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Interoperable with existing infrastructure
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Well understood fail-over and scaling model
●
Many regulatory issues already dealt with
–
●
Billing, CALEA/LI, Privacy
It's taken almost 10 years to sort out the SIP
issues. Why start from scratch and make the
same mistakes all over again?

12. SIP over WebSocket
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draft-ietf-sipcore-sip-websocket
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WebSocket has limitations
–
You can't know your local IP address
–
It's basically a NAT traversal issue
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Use Path (RFC 3327)
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Use SIP Outbound (RFC 5626)
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Use GRUU (RFC 5627)

13. SIP over WebSocket is widely available
●
Open-source server implementations
–
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Asterisk, Kamailio, OverSIP, reSIProcate
Open-source client implementations
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JAIN SIP JavaScript
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JsSIP
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QoffeeSIP
–
sipML5

14. But what about presence and messaging?
●
●
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SIP page-mode messaging is great for one-ata-time messages
MSRP is well suited for light-weight sessionbased messaging and file-transfer
XMPP is the right solution for advanced
messaging, network address book, and
presence

15. XMPP and SIP together?
●
SIP is best for media session establishment
and interoperability
●
XMPP is better for messaging and presence
●
Use the right protocol for the job
●
CUSAX (Combined Usage of SIP And XMPP)
is the future

16. Efficient messaging
MSRP is a natural companion to SIP
● Can be used for IM, file transfer, or any other data streaming you
want
● MSRP over WebSocket
●
Involves an MSRP relay in the network (local policy can be enforced)
– Great for client to server data exchanges
– draft-pd-dispatch-msrp-websocket
–
●
MSRP over WebRTC
Low-latency, secure, structured messaging between peers
– Often a better option than XMPP messaging (even if using XMPP
network address book and presence) as it is peer-to-peer
– draft-pd-msrp-webrtc
–

17. MSRP over WebSocket
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Open-source server implementations
–
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Kamailio
Open-source client implementations
–
Crocodile MSRP
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draft-pd-dispatch-msrp-websocket supported now
draft-pd-msrp-webrtc supported soon

18. Crocodile RCS Ltd
www.crocodile-rcs.com