1 interactive multimedia satellite access communications tho le-ngoc, mcgill university victor...
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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) <> CRA / RBDC Assured Forwarding(AF) <> RDBC Default(DE) <> 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?