This presentation presents our paper that evaluates an extension of a production WebRTC-based video conferencing system that enables seamless dynamic switching between one-on-one and group mode as participants join or leave a conference. The two modes have different transport types; In the one-on-one case the call is relayed only if the two endpoints cannot establish a direct connection, whereas in the group case the call is always routed through a Selective Forwarding Unit (SFU). We examine the different sets of features that should be used in each mode and we perform a measurement study to explore the impact of the extension on the infrastructure costs and on several connection properties such as media latency, call establishment time, packet loss and throughput.

1. Experimental Evaluation of
Dynamic Switching between One-
on-One and Group Video Calling
George Politis | github.com/gpolitis | @jitsinews
tiny.cc/p2p4121-presentation
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2. Jitsi Meet Overview
• Jitsi Meet (Open Source) Stack
• meet.jit.si cloud
• meet.jit.si metrics
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3. Jitsi Meet Stack
Jitsi Meet for the Web
(WebRTC JS APIs)
Jitsi Meet for Mobile
(React Native WebRTC)
JiCoFo
(Signaling Server)
Jitsi Videobridge
(Media Server/SFU)
Client Side
Server Side
XMPP (Prosody) UDP/DTLS/SRTP
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4. Jitsi Meet
• Multiple Layouts
• Video Quality slider
• Speaker stats
• Desktop sharing
• Integrated Chat
• callstats.io integration
• Transcriptions
• Recording to Dropbox
• Telephony support
(web & mobile app)
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5. Jitsi Videobridge
• Implements Google
Congestion Control
• Adaptive Simulcast/SVC
• Adaptive Last-N
• XMPP API
• REST API
• callstats.io integration
media server/SFU
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6. Signaling
components
SFU 1 SFU 2
SFU N
HA Proxy
Cluster
…
…
Shard N
AWS Region Z
AWS Region X
AWS Region Y
Shard 1
TURN
meet.jit.si Cloud
• Horizontal scaling through
Sharding
• Geo-distributed HA Proxy
cluster routes participants
to shards
• AWS Regions: North
Virginia, Oregon, Ireland,
Australia
• Beefy dedicated C4.xlarge
for SFU & TURN servers
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7. meet.jit.si Metrics
• 91,408 conferences
• Average conference duration 38 min
• Average participant count 3.37
• 3.47M conferencing minutes
• 7.25M participant minutes
• Average RTT: 296ms
• Average Upload: 1110 kbps
• Average Download: 563 kbps
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8. P2P4121
(aka peer-to-peer for one-to-one)
• Congestion control
• Group call vs one-on-one call mode
• Other implementations
• Jitsi meet implementation
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9. Google Congestion Control
• Network congestion directly
impacts Quality of Service (QoS)
• Google Congestion Control cues:
• Packet delay variation
• Packet loss
• Standard RTCP & REMB or
Transport Wide Congestion
Control Header and RTCP
feedback
• Implemented in the browser/
mobile and in the SFU
Media
Target bitrate
2.5Mbps
Packet arrival times
Packet loss
Sender
Receiver
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10. One-on-one vs Group mode
Media
Target bitrate
2.5Mbps
Packet arrival times
Packet loss
Sender
Receiver
Sender A
Receiver
SFU
simulcast
3.2Mbps
Simulcast filtering
Last-N filtering
Sender B Sender C
simulcast
3.2Mbps
2.5Mbps
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11. Other implementations
✅ Google Hangouts (Feb 2016)
✅ Jitsi Meet (July 2017)
✅ Slack Video (June 2018)
❓Facebook Video
❓Skype
❓Apple FaceTime
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12. P2P4121 Operation
• Participants enter in group-
call mode.
• The group-call mode
connection is maintained at
all times.
• If #participants == 2 for
more than X seconds, enter
one-on-one call mode
• If #participants > 2, fall
back to group-call mode
SFU
Participant A Participant B
Group mode
connection
Group mode
connection
One-to-one mode
connection
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13. Results
• Compare measurements from two periods: pre-P2P4121
and post-P2P4121
• Client side: WebRTC Statistics API => Splunk
• Server side: DataDog monitoring
• Infrastructure resource use: transferred data, SFU IO stats
• Quality of Service: RTT, call establishment time,
download/upload throughput
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14. Conferencing-time
• Pre-P2P4121
• 23470 conferences
• 689273 minutes
• Post-P2P4121
• 23320 conferences (-0.5%)
• 696311 minutes (+1%)
6-way or more
2.6%
5-way
2.0%
4-way
5.4%
3-way
12.2%
One-on-one
77.8%
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15. Transferred data
Change -49%
Terrabytes
Downstream Upstream Combined
6.3
2.7
3.6
13.1
6
7.1
Change -52%Change -55%
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16. SFU IO
Percent
CPU
3.2%
4.7%
Megabytes
Memory
2,420
3,740
Change -35% Change -32%
Numberofprocesses Load
0.15
0.28
Change -46%
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17. Roundtrip-time
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18. Average Round-trip time
end-to-end RTT for
server-relayed calls
RTT for direct
connect calls
% change
N. Virginia (US) 157 ms 122 ms 22.3% shorter
Ireland (EU) 132 ms 92 ms 30.3% shorter
16% shorter 24.6% shorter
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19. Upload bitrate
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20. Download bitrate
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21. Average down/up bitrate
Download
/Upload TURN-relayed Direct connect SFU-relayed
Ireland (EU)
1307 Kbps
/1281 Kbps
1217 Kbps
/1207 Kbps
819 Kbps
/1349 Kbps
(60% efficiency)
N. Virginia (US)
1108 Kbps
/1045 Kbps
1209 Kbps
/1169 Kbps
655 Kbps
/1245 Kbps
(52% efficiency)
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22. Conclusion
• 52% reduced bandwidth
• 35%-40% infrastructure pressure (memory/CPU/load)
• 20%-30% shorter RTT (depending on the region)
• TURN throughput ~= direct connect throughput
• Group call features reduce one-on-one call throughput
efficiency: 52%-60%
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23. Thank you!
GEORGE POLITIS | GITHUB.COM/GPOLITIS | @JITSINEWS
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