Multimedia Support in Enterprise Remote Desktop Environment transport mechanisms for WANs

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Multimedia Support in Enterprise Remote Desktop
Environment transport mechanisms for WANs

• Presentation by Marcin Lubonski
• Supervisors Dr Valerie Gay (UTS), Dr Andrews
  Simmonds (UTS), Dr Steve Parry (Citrix Systems)
• University of Technology Sydney
• Email marcin_at_it.uts.edu.au

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Presentation Roadmap

• Introduction
• How do thin-client systems and video fit
  together?
• Research motivation and brief methodology
  overview
• Process
• Define goals
• Data collection
• Analyse results and formulate hypothesis
• Verify initial proposition by prototyping
• Summary
• Future directions and Open Issues

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Thin-client systems - overview

• Def. Thin-client system Thin-client Remote
  Desktop System
• You probably used/seen one
• Usually by the universities, in enterprise
  environment, for personal purposes
• Popular systems on the market
• Citrix Presentation Server, MS Terminal Services,
  VNC, NX, X server, Sun Ray, Sun Tarantella, etc.
• Designed in 80s 90s to work in LAN with classic
  desktop apps.
• The challenge complex graphics and multimedia

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Research Motivation

• Research objective Better multimedia experience
  in thin-client over WAN
• Address limitations such as
• Long-delay links on thin-client protocols
  performance
• TCP performance (especially in WAN)
• Common transport layer for
• real-time
• interactive applications

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Research Outline

• Thin-client architectures and technologies
  (S-o-A)
• Performance evaluation of thin-client protocols
• Proposition of a transport protocol for
  thin-client
• Implementation, integration with thin-client
  protocol and evaluation
• Continuous dissemination of results and
  applicability in other areas

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Local and remote display architecture
User Input
GUI Application
Display and Windowing System
Operating System
Video Device Driver
Video Graphics Card
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Video in Remote Desktop Systems (1)

• Multimedia extension in Citrix Presentation
  Server RAVE (Citrix Systems, 2001)

Application
DirectShow
DirectSound
Graphics Device Interface (GDI)
User-level
Kernel-level
Device Driver Interface (DDI)
DirectDraw ( HAL DDI)
DirectSound ( HAL DDI)
Windows - specific
Video Device Driver
Sound Device Driver
Video Graphics Card
Sound Card
Sockets
Thin-client
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Video in Remote Desktop Systems (2)

• Virtual Display Architecture THINC system
• Source (R. Baratto, 2001)

Application
X Server
ALSA-based Sound Driver
THINC Virtual Video Driver
THINC Sound Server
Video Graphics Card
Sound Card
Sockets
Thin-client
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Thin-client protocol stacks

• Thin-client protocols are system specific, often
  proprietary and closed-source
• Thin-client protocol characteristics

() Updated version based on (J. Nieh, 2003)
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Thin-client Protocol-Multiple Application Streams

• Thin-client protocols combine multiple
  application streams, e.g. desktop updates, video,
  file system operations

Stream 1 Video
Stream 2 Desktop Updates
GUI Application
Packet Scheduling
.
Stream n File System
Application-layer
Transport-layer
Single Connection
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Transport-level Limitations

• Current thin-client protocols stack
  transport-level limitations
• Application flows not separated on transport
  layer (Real-time and reliable data multiplexed)
• Reliable transport for real-time data
• Stream-oriented not message-oriented transport
  used
• Transport protocol not suited for WAN environment

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Presentation Roadmap

• Introduction
• Research overview and brief methodology overview
• How do thin-client systems and video fit
  together?
• Process
• Define goals
• Collect supporting data
• Analyse results and formulate hypothesis
• Verify initial proposition by prototyping
• Summary
• Future directions and Open Issues

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Tests Motivation and Methodology Used

• Performance Engineering Process
• Tests goal identify the main performance
  limitations
• Thin-client protocol interflow interference
• Multimedia quality degradation with packet loss,
  delay and jitter (impact of TCP)
• Reliability impact on
• performance of real-time applications
• response time of interactive app. (network delay)

Define goals ? Collect supporting data ? Analyse
results and formulate hypothesis ? Verify initial
proposition by prototyping
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Data collection

• Tests run for mainstream thin-client systems
• WAN characteristics emulated in testbed
• Automated to minimize human errors
• Used methods for application quality assessment
• Replay of pre-recorded user sessions (response
  time),
• Slow-motion benchmarking (J. Nieh, 2003) and
  Video Quality Index (video),
• Peak Signal to Noise Ration and Frame Marking
  (video),
• Transport protocol tunnelling (TCP congestion
  control).

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Data collection - Testbed Design
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Test Scenarios and Metrics Used

• Test scenarios
• Response time tests for interactive applications,
• Video quality assessment with network packet
  loss, delay, jitter,
• Video quality vs. TCP congestion control.
• Metrics
• Response time
• average response time between user clicks,
• reported by application delay between
  application-level messages.
• Video quality
• Peak Signal to Noise Ratio,
• Slow-motion Benchmarking with Video Quality
  Index.

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Response Time Results
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Video Quality Index Delay (large rcwnd)
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Observed Frame Rate Network Delay
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Observed vs. theoretical TCP throughput
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Other Results

• Presented here only delay results
• Delay the main performance prohibiting factor
  also refer to (A. Lai et al., 2002)
• Video quality (VQI, PSNR) vs loss, delay, jitter,
  reordering, or/and corruption
• Response time vs loss, delay, etc.
• User session scalability tests vs. concurrent
  users

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Formulate Hypothesis

• Impact of TCP
• Retransmissions Longer response time
• Unfair network share - TCP RTT-bias
• Congestion Control throughput underutilization
• Data flows multiplexing anomalies
• Interflow interference
• Late or unnecessary retransmissions (when
  multiplexed with unreliable/partially reliable
  data)
• ? New Transport Layer with Video Support for
  Thin-client

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Transport Layer with Video Support for Thin-client
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Transport Layer with Video Support for Thin-client

• Basic design objectives
• Minimise delay for real-time and interactive
  applications protocol should support for both
  reliable and unreliable/partially reliable
  delivery semantics
• Limit interference of separate application flows
  - independent data flows separation should be
  supported by transport layer without a need to
  open multiple parallel sockets
• Preserve application-level message boundaries -
  Delivery semantics should support
  message-boundaries in contrast to stream-oriented
  TCP-like delivery

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Prototyping Protocol Architecture
Stream 1 Video

GUI Application
Packet Scheduling
Stream 2 Desktop Updates

Stream n File System
Application-layer
Transport-layer
Stream 1

Stream 2

Stream n

• Tight coupling between thin-client and transport
  protocols required

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Why tight coupling? - Classic Encapsulation
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Video Stream
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Desktop Updates
Application Buffer
File System Operations
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Packet scheduling
10
16
25
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14
15
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Thin-client Protocol Packetization
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15
10
16
25
Transport Protocol Packetization
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Why tight coupling? - Advanced Protocols
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File System Operations Buffer
Desktop Updates Buffer
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28
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Video Buffer
11
27
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Packet scheduling
10
16
25
17
14
15
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Thin-client Protocol Packetization
14
15
10
16
25
Transport Protocol Packetization
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Packet Encapsulation in Proposed Protocol
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28
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File System Operations Buffer
Desktop Updates Buffer
12
27
19
Video Buffer
11
26
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Packet scheduling
10
16
25
17
14
15
Thin-client Protocol Packetization
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15
10
25
Transport Protocol Packetization
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Prototyping the Solution

• SCTP as transport for thin-client
• SCTP Pros
• Multiple streams support - no interflow
  interference, no head-of-queue problem
• Reliable and unreliable traffic (PR-SCTP
  extensions) - real-time vs. interactive
• Connection Heartbeat prevents connection
  timeout
• Comprehensive application notification API -
  application can adapt to network state
• SCTP Cons
• RTT-bias due to TCP NewReno congestion control
• FIFO packet scheduling (no support for packet
  priority)

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Implementation - Extensions to SCTP

• To address SCTP limitations
• TCP NewReno RTT-bias
• Separate congestion control and flow control in
  SCTP implementation
• Allow configurable congestion control for each
  SCTP stream
• Dumb FIFO Packet Scheduling
• Modify packet scheduling algorithm to Shortest
  Deadline First (possibly experiment with
  Weighted-Fair Queuing)

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Implementation - Choice of Thin-client System

• Integrate with the system supporting multimedia
  i.e. Citrix Presentation Server or THINC
• Pains working with a commercial solution
• Access to the system sources, Platform dependant
  solution, Architectural concerns, Legal issues
• Difficulties working with academic system
• Legal Issues (still !!!), Limited Support
• Altogether THINC wins!

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Verification - Performance Tests
GUI App
GUI App
Thin-client
Application video quality, response time, per
stream goodput
THINC
THINC
Transport retransmissions, link utilization
TCP
SCTP
TCP
SCTP
IP
IP
WAN Environment
Client
Server
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Presentation Roadmap

• Introduction
• Research overview and brief methodology overview
• How do thin-client systems and video fit
  together?
• Process
• Define goals
• Collect supporting data
• Analyse results and formulate hypothesis
• Verify initial proposition by prototyping
• Summary
• Future directions and Open Issues

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Future Work and Open Issues

• Open Issues
• No suitable congestion control exists for
  multimedia
• Protocol Platform Independence
• Future Work possible directions
• RTP over SCTP
• Thin-client over SCTP and Wireless Networks
• Extra Reliability by Congestion Control Block
  (CCB) Scaling
• SCTP multihoming and mobility
• Subflow SCTP 1..n CCBs per each SCTP stream
• QoS-aware application-layer multicast based on
  SCTP
• Reduce Delay Even More - Forward Error Correction

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Conclusions

• Thin-client Systems not Ready for Multimedia
• No Transport Support for Multimedia Extensions
• Main Performance Problems
• Network Delay Impact (late retransmissions,
  unfair throughput share)
• TCP Limitations (only reliable transport
  semantic, too conservative congestion control)
• We Proposed Protocol
• Configurable Congestion Control, Reliable and
  Unreliable semantic, Application Streams
  Separation

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References

• Baratto R. A., Kim L. N., and Nieh J., "THINC a
  virtual display architecture for thin-client
  computing," in Proceedings of the twentieth ACM
  symposium on Operating systems principles.
  Brighton, United Kingdom ACM Press, 2005, pp.
  277-290.
• Citrix Systems Inc., "SpeedScreen Multimedia
  Acceleration a.k.a Remoting Audio and Video
  Extensions," Citrix Systems, Engineering
  Functional Specification, July 2003.
• Lai A. and Nieh J., "Limits of wide-area
  thin-client computing," in Proceedings of the
  2002 ACM SIGMETRICS international conference on
  Measurement and modeling of computer systems.
  Marina Del Rey, California ACM Press, 2002, pp.
  228-239.
• Jason N., Yang S. Jae , and Novik N., "Measuring
  thin-client performance using slow-motion
  benchmarking," ACM Transactions of Computer
  Systems, vol. Vol. 21, pp. 87-115, 2003.

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Metrics used

• Video Quality Index with slow-motion
  benchmarking
• Frame Marking - Custom metric based on Peak Noise
  to Signal Ratio (PSNR)

Marker
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Slow-motion Benchmarking

• Full speed video playback

• Slow-motion video playback

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Theoretical TCP Throughput

• Throughput
• 1/sqrt(p)
• 1/RTT
• Packet loss (p)
• Different in LAN, WAN, WLAN
• Delay (RTT)
• LAN - lt 10ms
• WAN 100-300ms
• Sattellite gt 500ms

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TCP Reno - RTT Bias
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Transport Protocol Tunnelling
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Video Quality vs. Congestion Control