Interactive Multimedia Satellite Access Communications

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Interactive Multimedia Satellite Access
Communications

• Tho Le-Ngoc, McGill University
• Victor Leung, University of British Columbia
• Peter Takats and Peter Garland, EMS Technologies

Appear in IEEE Communications Magazine, July
2003 Reviewed by Huakai Zhang, 12/4/2003
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Outline

• Introduction Broadband Satellite Access(BSA)
• Objective
• IP-Based BSA Systems
• TCP over BSA Systems
• Conclusion

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Introduction

• Collaborative research in telecommunications
• A Canadian experience
• Dynamic satellite bandwidth allocation
• An architecture for DiffServ provisioning over
  BSA systems
• A dynamic TCP Vegas protocol as a proxy service
  for split-TCP connections over BSA systems

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Introduction

• Satellite Communication
• An alternative to traditional(terrestrial)
  communication
• Most satellites operate in the microwave region
• Microwave satellites operate on assigned
  frequency bands designated by a letter. Common
  communications satellite bands are the C (3.4 to
  6.425 GHz) and Ku (10.95 to 14.5 GHz) bands

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Introduction (cont)

• BSA system configuration

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Introduction (cont)

• Example (Digital Video Broadcast DVB-RCS)

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Introduction (cont)

• Broadband Satellite Access(BSA)
• Pros
• 1. Provide connectivity in remote areas,
  continental coverage
• 2. Avoid unpredictable congestion and delay (only
  one hop)
• 3. Ideal for real-time multicast and broadcast
  services
• Cons
• 1. Lack of economical satellite-based
  return/interaction
• 2. High cost compared to terrestrial technologies

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Objective

• Dynamic Capacity Allocation
• All User Terminals(UTs) share
• the same return link using a
• Multi-Frequency Time-Division
• Multiple Access (MF-TDMA)
• scheme, which needs to be dynamic
• to ensure efficient return link
• utilization.

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Objective (media access method 1)

• Random Access ALOHA
• No channel setup/tear-down, but limited channel
• utilization
• Ideal for low data rates/fast response app.,
  such as
• bank transactions

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Objective (media access method 2)

• Demand Assigned Multiple Access (DAMA)
• High QoS, but need setup phase to reserve
  capacity
• Ideal for VoIP and Video Conf. use pre-defined
• constant bit rate, i.e PAR 1

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Objective (media access method 3)

• Combined Free/DAMA (CFDAMA)
• Freely allocate the remaining capacity to the
  UTs to make
• the response time small, while keeping good QoS
  and high
• channel utilization
• Ideal for bursty multimedia services with
  diverse QoS
• requirements

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Objective (method 2 vs. method 3)
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IP-Based BSA Systems

• Goal
• End users are assumed to be IP-based.
• It is desirable for BSA systems to interoperate
  seamlessly with the terrestrial IP networks and
  to be compatible with IP-based technologies and
  protocols.

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IP-Based BSA Systems (cont)
User Traffic Protocol Stack
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IP-Based BSA Systems (cont)
T1, T2 handles DiffServ Packet
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IP-Based BSA Systems (cont)
Simplified drawing of DiffServ Implementation
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IP-Based BSA Systems (cont)

• Representation of bandwidth assignment with
  coordinates of (time, frequency)

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IP-Based BSA Systems (cont)

• DVB-RCS bandwidth allocation mechanisms
• Continuous Rate Assignments (CRA), VoIP
• Rate Based Dynamic Capacity (RBDC), Web
  traffic
• Volume Based Dynamic Capacity (VBDC), Email
• Absolute Volume Based Dynamic Capacity (AVBDC)
• Free Capacity Assignment (FCA)
• Mapping for the DiffServ PHB and DVB-RCS
• Expedited Forwarding(EF) ltgt CRA / RBDC
• Assured Forwarding(AF) ltgt RDBC
• Default(DE) ltgt FCA / VBDC

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TCP over BSA Systems

• Why TCP throughput is degraded in satellite
  links?
• High delay-bandwidth networks with short
• connection and TCP flow control (e.g. WWW
  traffic)
• (high packet loss rate, long RTTs)

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TCP over BSA Systems (cont)

• Solutions
• Link Layer Retransmission and error correction
• End-to-end Extension/options of TCP, e.g. slow
  start modification, but very limited
• Performance Enhancement Proxy (PEP)
• The most effective one, containing virtual
  TCP senders/receivers between terrestrial IP
  networks and satellite links

Solutions have to cope with end-user transparency
and/or protocol stack redefinition
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TCP over BSA Systems (cont)

• Proposed TCP Proxy Service
• Dynamic congestion control mechanism (DVgas),
  uncoupling of flow control and error recovery
  mechanisms.
• Active Queue management by RED
• Immediate Feedback Mechanism results in few
  dropped packets

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TCP over BSA Systems (cont)

• Performance

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TCP over BSA Systems (cont)

• Effects of Traffic Load and BER on throughput

100 with 10-7 BER, 80 with 10-7 and 20 with
10-6 BER, 20 with 10-6 BER
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Conclusion

• This paper gives an overview of key innovations
  on BSA system architecture.
• CFDAMA offer short delay, high channel
  utilization.
• It is suitable for DiffServ provisioning over BSA
  systems
• A proxy service to improve TCP performance is
  presented.

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Question?