This document proposes Raabta, a low-cost video conferencing system for developing regions. Raabta leverages existing analog cable TV networks and uses inexpensive Raspberry Pi devices as endpoints. It was designed with principles of low cost, low power usage, tolerance of failure-prone environments, and a simple interface. The system avoids reliance on internet connectivity by using the cable networks for both upstream and downstream video streams encoded for robust transmission. This approach could enable affordable, widespread communication tools for communities with limited infrastructure and resources.

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
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Raspberry-Pi instances as end-hosts
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Video conferencing application co-design
–
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Multi-layered encoding and dynamic recovery
Simple text-free interface

3. Outline
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Motivation
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Background
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Design Goals
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Raabta
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Beyond Raabta
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Conclusion and Future Work

4. Motivation
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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
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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.
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Both backbone and last-mile access
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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
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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

11. Raabta

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:
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Use non-TV channels for video conferencing
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Same band for upstream/downstream
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Delegate MAC operation to end-host
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Replace uni-directional amplifiers with bi-directional
ones

14. Raabta: MAC Layer
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No centralized arbitration
1) FDMA
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Slice up free spectrum into equi-sized slots
200KHz ensures 700Kbps for very good quality video
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135 end-hosts
25KHz ensures 84Kbps for reasonable QoE
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1480 end-hosts
2) CSMA/CD
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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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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
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Also broadcast regularly
2) Multi-layer encoding
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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
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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:
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Anil Madhavapeddy
for comments and
suggestions
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Arjuna Sathiaseelan
and Jon Crowcroft
for arranging remote
talk
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Images:
FreeDigitalPhotos.net,
Berkeley TIER,
wikimedia.org, and
evidence4action.net