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Raabta: Low-cost Video Conferencing for the Developing World
1. Raabta: Low-cost Video
Conferencing for the
Developing World
Zubair Nabi
zubair.nabi@cantab.net
Information Technology University, Pakistan*
MobiCom Workshop on
Lowest Cost Denominator Networking for Universal Access
30 September, 2013
* Now at IBM Research, Dublin
2. Raabta
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Leverage existing analog cable TV networks to
provide video conferencing
●
Raspberry-Pi instances as end-hosts
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Video conferencing application co-design
–
●
Multi-layered encoding and dynamic recovery
Simple text-free interface
4. Motivation
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●
●
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Daily income for > 50% of the world: < $2
The Internet has the power to improve the
human condition
10% increase in broadband Internet penetration
leads to 1.4% increase in GDP (World Bank)
Cognizance of social, economic, and
technological conditions
5. Proposed Solutions
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Challenges:
–
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Intermittent and bad power
–
Extreme weather conditions: dust, humidity, etc.
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Frequent equipment failure
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Lack of trained local workforce
–
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Monetary and engineering costs
Rolling investment required
WiMAX, satellite, long-distance WiFi, ZigBee,
optical, cellular etc.
–
Both backbone and last-mile access
–
Also plagued by shortcomings
6. Observations
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Internet access not an underpinning technology
–
●
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Backbone access extremely expensive
Basic, community-wide communication required
Systems designed for the developing world illsuited due to fundamental differences, such as
low population density
7. Design Goals
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Cost: as low as possible
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Power: low power draw
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Failure: norm rather than exception
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User-interface: simple enough to be used by
low-literate people
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Internet connectivity: not a requirement
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Infrastructure: leverage existing
●
Operational sustainability: self-managing
8. Background: Analog Cable
Networks
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Broadcast-based shared medium
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Downstream traffic (Gbps): [4.9, 6.6]
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Cable modem as MAC layer bridge
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Link-layer protocol can be offloaded
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At least 12 million people in rural areas in
Pakistan own a TV and 3.9 million have cable
connections (Gallup)
9. Background: Raspberry Pi
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General-purpose single board computer
Broadcom system-on-chip processor: ARM
700MHz processor, 24GFLOPS GPU, and
integration audio and video
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Multiple video output options
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Optional Ethernet
10. Background: Video Conferencing
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3 functional aspects:
1) Overlay topology
2) Encoding scheme
3) Packet loss recovery
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High-bandwidth and low-latency requirement
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Tolerance to device and network heterogeneity
12. Raabta: End-host
Component
Raspberry Pi Model B
Camera Board
External Cable Modem
USB Sound Card
USB Keyboard
USB Mouse
Headset
Total
Cost ($)
35
25
20
7
2
2
1
92
13. Raabta: Network
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Status-quo: Downstream spectrum: 50860MHz, 6MHz per channel (42Mbps: 256QAM), 135 channels
Key modifications:
–
Use non-TV channels for video conferencing
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Same band for upstream/downstream
–
Delegate MAC operation to end-host
–
Replace uni-directional amplifiers with bi-directional
ones
14. Raabta: MAC Layer
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No centralized arbitration
1) FDMA
•
•
Slice up free spectrum into equi-sized slots
200KHz ensures 700Kbps for very good quality video
•
•
135 end-hosts
25KHz ensures 84Kbps for reasonable QoE
•
1480 end-hosts
2) CSMA/CD
•
Treat entire spectrum as a large shared channel
•
•
•
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37MHz, 258Mbps, 1.6ms RTT, 51600byte minimum frame size
51600 MPEG frame: 51580 payload + 4 header + 16 FEC
Each modem listens for its MAC or broadcast address
Explore different points in the design space
15. Raabta: Network Layer
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LAN so network layer not required but
unmodified IP used
2 key advantages:
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–
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Potential wider Internet connectivity
IP multicast for efficient multi-party conferencing
Distributed protocol for dynamic address
allocation
16. Raabta: Transport Layer
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Vanilla RTP atop UDP
Each RTP packet: timestamp, sequence
number, and payload format
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RTCP for synchronization across streams
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For each call, 4 streams initiated
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One stream each for audio and video
–
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SIP for destination port selection
Two streams for synchronization
Packet loss: dynamic switching b/w FEC and
selective acks based retransmission
17. Raabta: Video Conferencing
1) User database
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Init: Broadcast user ID, picture, and IP
•
Also broadcast regularly
2) Multi-layer encoding
•
•
Base layer + additional incremental layers
Resilient to high loss, quality of video determined by
recipient downlink capacity
3) UI
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Text free, although optional text messaging
•
Picture-driven with audio feedback
18. Beyond Raabta
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Internet connectivity
–
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Community-wide applications
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Simple to extend using low-cost solutions
Telemedicine, distance learning, etc
Operator incentive
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Simple management due to decentralization
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No additional operational or power cost
Flat monthly rate
Leveraging existing infrastructure
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Community needs to focus on this
19. Conclusion and Future Work
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Possible to provide low-cost video conferencing
using existing infrastructure and simple
components
Future work:
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Implementation and evaluation of the system
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Closer inspection and analysis of MAC
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Deployment in the wild
20. Q?
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Acknowledgments:
–
Anil Madhavapeddy
for comments and
suggestions
–
Arjuna Sathiaseelan
and Jon Crowcroft
for arranging remote
talk
–
Images:
FreeDigitalPhotos.net,
Berkeley TIER,
wikimedia.org, and
evidence4action.net
