Experiences with High-Definition Video Conferencing

Experiences with High-Definition
Video Conferencing

Colin Perkins, Alvaro Saurin
University of Glasgow, Department of Computing Science

Ladan Gharai, Tom Lehman
University of Southern California, Information Sciences Institute

Talk Outline

• Scaling multimedia conferencing
• The UltraGrid system
– Hardware requirements
– Software architecture
• Experimental performance
• Challenges in congestion control
• Conclusions
Copyright © 2006 University of Glasgow
All rights reserved.

Scaling Multimedia Conferencing

• Given advances in system power, network bandwidth and video
cameras, why are video conferencing environments so limited?

Why are we stuck with low quality 288
images…?

352


Why do conferencing systems look like this?


…and not like this?

Research Objectives

• To explore the problems inherent in delivering high definition
interactive multimedia over IP:
– Related to the protocols
– Related to the network
– Related to the end-system

• To push the limits of:
– Image resolution, frame rate and quality
– Network and end system capacity

• To demonstrate the ability of best effort IP networks to support
high quality, high rate, media with effective congestion control

UltraGrid: High Definition Conferencing
Build an HDTV conferencing demonstrator:
• Standard protocols 1999 HDTV work at ISI starts
– RTP over UDP/IP Nov. 2001 Demo at SC’01, Denver
– HDTV payload formats & TFRC profile (24 bit colour, 45 fps ⇒ 650Mbps
– Best effort congestion controlled delivery Jan. 2002 Public code release
no additional QoS (BSD-style open source license)
• Commodity networks Nov. 2002 Demo at SC’02, Baltimore
– High performance IP networks (24 bit colour, 60fps ⇒ 1.0 Gbps)
• OC-48 or higher
Apr. 2005 Full uncompressed HDTV
• Competing with other IP traffic
(30 bit colour, 60fps ⇒ 1.2 Gbps)
– Local area up to 10 gigabit Ethernet
Sep. 2005 RFC 4175
• Commodity end systems Demo at iGrid’05, San Diego
– PC or similar workstation
Nov. 2005 Demo at SC’05, Seattle
– HDTV capture and display

UltraGrid: The first HDTV conferencing system using commodity hardware

Media Formats and Equipment
• Capture and transmit a range of video formats:
– Standard definition video:
• IEEE 1394 + DV camera
– High definition video:
• DVS HDstation or Centaurus capture card
– 100MHz PCI-X
– 720p/1080i HDTV capture from SMPTE-292M
– Approx. $6,000
• Video data rates up to 1.2Gbps
• Chelsio T110 10-gigabit Ethernet
• Dual processor Linux 2.6 system

1280

720

720
576

352

288

CIF/288 lines PAL/576 lines HDTV/720p

Media Formats and Equipment

• A variety of HDTV cameras are now available:
– Broadcast quality cameras:
• Generally expensive ~$20,000
– Panasonic AJ-HDC27F
– Thomson LDK 6000
• SMPTE-292M output ⇒ directly connect to UltraGrid, low latency
– Consumer grade cameras:
• Price is in the $3,000–5,000 range
– Sony HVR-Z1E, HDR-FX1
– JVC GY-HD-100U HDV Pro
• No SMPTE-292M output ⇒ converter needed (E.g. AJA HD10A), higher
latency

• Displays must accommodate:

– 16:9 aspect ratio

– 1280×720 progressive or 1920×1080 interlaced

Software Architecture
• Classical media tool architecture
– Video capture and display
– Video codecs
• DV and M-JPEG only at present,
others can be added
– RTP
– Adaptive video playout buffer

• Two interesting additions:
– Congestion control over RTP

– Sophisticated video sending buffer

Experimental Performance
AJ-HDC27F
Seattle, WA
SC 2005
UG sender

10 G
bs Et
hern
UG et
receiver LDK 6000
Chicago

Arlington, VA
Los Angeles UG sender
ISI-East
• Wide area HDTV tests OC
-19
on the Internet2 backbone 2S
ON
ET
/SD UG
H
– ISI-East ⇔ ISI-West receiver

– ISI-East ⇔ Denver (SC’01)
Houston
– ISI-East ⇔ Seattle (SC’05)
• Demonstrated interactive low-latency uncompressed HDTV conferencing
between ISI-East and Seattle at SC’05
– Gigabit rate bi-directional video flows (tested using both HOPI and Abilene)

• Ongoing low-rate tests between ISI-East and Glasgow using 25 Mbps DV

format video

Experimental Performance

• Environment:
– Seattle ⇔ ISI-East over Abilene; 14-18 November 2005
– Best effort IP service, non-QoS enabled, shared with production traffic
– 8,800 byte packets; 10 gigabit Ethernet w/jumbo frames; OC-192 WAN

• Packet loss:
– Overwhelming majority of RTCP reports showed no packet loss
– Occasional transient loss (≤0.04%) observed due to cross traffic
• Inter-packet interval: Inter-packet interval (measured at receiver)

– Inter-packet interval (jitter) shows
expected sharp peak with long tail
– Network disrupts packet timing:

not significant for the application
• Playout jitter buffer compensates

Deployment Issues

• Good performance on Internet2 – usable today
– Observe occasional loss due to transient congestion
• HDTV flows not TCP-Friendly, cause transient disruption during loss periods
– Cannot support large numbers of uncompressed HDTV flows
• But active user community exists in well provisioned regions of the network
(UltraGrid nodes in US, Canada, Korea, Spain, Czech Republic...)

• Two approaches to wider deployment
– Optical network provisioning and/or quality of service
• E.g. Internet2 hybrid optical packet network (HOPI) also used for some tests
• Possible, solves problem, but expensive and hard to deploy widely
• Necessary for guaranteed-use deployments
– Congestion control

• Adaptive video transmission rate to match network capacity
• Preferred end-to-end approach for incremental, on demand, deployment

• Necessary for safety, even if QoS provisioned network available

Congestion Control for Interactive Video

• TCP not suitable for interactive video
– Abrupt variations in sending rate
– Couples congestion control and reliability
– Too slow
• Obvious alternative: TCP-Friendly rate control (TFRC)
– Well specified, widely studied rate-based congestion control
– Aims to provide relatively smooth variations in sending rate
– Doesn’t couple congestion response and reliability

– Two implementation choices: • DCCP implementations not mature
• Use DCCP with CCID 3 • Deployment challenges due to firewalls
• Not feasible to use at this time
• Use RTP profile for TFRC

• Can be deployed in end systems only (running over UDP)

• Easy to develop, deploy, debug and experiment with code

TFRC Implementation

• Rate based algorithm,
clocking packets from
sending buffer
• Sending buffer size chosen to respect 150ms one
way latency constraint (⇒ a couple of frames)
• Rate based control driving queuing system:
– Widely spaced (16ms) bursts of data from codec
– Fast, smoothly paced, transmission (~70µs spacing)
• Mismatched adaptation rates

– TFRC ⇒ O(round-trip time)
– Codec ⇒ O(inter-frame time)

– Relies on buffering to align rates, varies codec rate ⇒ problematic for stability

TFRC Performance
Transport protocol stable on large RTT
paths, less stable for shorter paths

Video rate can follow congestion control
rate, provided frame rate and RTT similar

Desired vs. actual sending rate

100ms RTT, 800kbps bottleneck, 10 fps M-JPEG
Testing in dummynet Throughput with varying RTT

Implications and Conclusions

• Well engineered IP networks can support very high performance
interactive multimedia applications
– The current Internet2 best effort IP service provides real-time performance
suitable for gigabit rate interactive video when shared with other traffic
– Transient congestion causes occasional transient packet loss, but recall that
we added a gigabit rate real-time video flow to an existing network without
re-engineering that network to support it

• Initial congestion control experiments raise more questions than
they answer
– Possible to implement, but more sophisticated codecs needed
– Difficult to match codec and network rates, causes bursty behaviour

• Impact on perceptual quality due to implied quality variation unclear
• Likely easier as video quality, frame-rate, and network bandwidth increase

UltraGrid

http://ultragrid.dcs.gla.ac.uk/
A High Definition Collaboratory

Experiences with High-Definition Video Conferencing

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