Raabta: Low-cost Video Conferencing for the

Developing World

Zubair Nabizubair.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

Raabta

● Leverage existing analog cable TV networks to provide video conferencing

● Raspberry-Pi instances as end-hosts● Video conferencing application co-design

– Multi-layered encoding and dynamic recovery

● Simple text-free interface

Outline

● Motivation● Background● Design Goals● Raabta● Beyond Raabta● Conclusion and Future Work

Motivation

● 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

Proposed Solutions

● Challenges:– Monetary and engineering costs

– Intermittent and bad power

– Extreme weather conditions: dust, humidity, etc.

– Frequent equipment failure

– Lack of trained local workforce

– Rolling investment required

● WiMAX, satellite, long-distance WiFi, ZigBee, optical, cellular etc.– Both backbone and last-mile access

– Also plagued by shortcomings

Observations

● Internet access not an underpinning technology– Backbone access extremely expensive

● Basic, community-wide communication required● Systems designed for the developing world ill-

suited due to fundamental differences, such as low population density

Design Goals

● Cost: as low as possible● Power: low power draw● Failure: norm rather than exception● User-interface: simple enough to be used by

low-literate people● Internet connectivity: not a requirement● Infrastructure: leverage existing● Operational sustainability: self-managing

Background: Analog Cable Networks

● Broadcast-based shared medium● Downstream traffic (Gbps): [4.9, 6.6]● Cable modem as MAC layer bridge● Link-layer protocol can be offloaded● At least 12 million people in rural areas in

Pakistan own a TV and 3.9 million have cable connections (Gallup)

Background: Raspberry Pi

● General-purpose single board computer● Broadcom system-on-chip processor: ARM

700MHz processor, 24GFLOPS GPU, and integration audio and video

● Multiple video output options● Optional Ethernet

Background: Video Conferencing

● 3 functional aspects:

1) Overlay topology

2) Encoding scheme

3) Packet loss recovery

● High-bandwidth and low-latency requirement● Tolerance to device and network heterogeneity

Raabta

Raabta: End-host

Component Cost ($)Raspberry Pi Model B 35Camera Board 25External Cable Modem 20USB Sound Card 7USB Keyboard 2USB Mouse 2Headset 1Total 92

Raabta: Network

● Status-quo: Downstream spectrum: 50-860MHz, 6MHz per channel (42Mbps: 256-QAM), 135 channels

● Key modifications:– Use non-TV channels for video conferencing

– Same band for upstream/downstream

– Delegate MAC operation to end-host

– Replace uni-directional amplifiers with bi-directional ones

Raabta: MAC Layer

● 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

• 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

Raabta: Network Layer

● LAN so network layer not required but unmodified IP used

● 2 key advantages:– Potential wider Internet connectivity

– IP multicast for efficient multi-party conferencing

● Distributed protocol for dynamic address allocation

Raabta: Transport Layer

● Vanilla RTP atop UDP● Each RTP packet: timestamp, sequence

number, and payload format● RTCP for synchronization across streams● For each call, 4 streams initiated

– SIP for destination port selection

– One stream each for audio and video

– Two streams for synchronization

● Packet loss: dynamic switching b/w FEC and selective acks based retransmission

Raabta: Video Conferencing

1) User database• 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• Text free, although optional text messaging• Picture-driven with audio feedback

Beyond Raabta

● Internet connectivity– Simple to extend using low-cost solutions

● Community-wide applications– Telemedicine, distance learning, etc

● Operator incentive– No additional operational or power cost

– Simple management due to decentralization

– Flat monthly rate

● Leveraging existing infrastructure– Community needs to focus on this

Conclusion and Future Work

● Possible to provide low-cost video conferencing using existing infrastructure and simple components

● Future work:– Implementation and evaluation of the system

– Closer inspection and analysis of MAC

– Deployment in the wild

Q?● 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