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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. Outline.
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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
Outline • Introduction: Broadband Satellite Access(BSA) • Objective • IP-Based BSA Systems • TCP over BSA Systems • Conclusion
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
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
Introduction (cont’) • BSA system configuration
Introduction (cont’) • Example (Digital Video Broadcast: DVB-RCS)
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
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.
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
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
Objective (media access method 3) • Combined Free/DAMA (CFDAMA) • Freelyallocate 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
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.
IP-Based BSA Systems (cont’) User Traffic Protocol Stack
IP-Based BSA Systems (cont’) T1, T2 handles DiffServ Packet
IP-Based BSA Systems (cont’) Simplified drawing of DiffServ Implementation
IP-Based BSA Systems (cont’) • Representation of bandwidth assignment with coordinates of (time, frequency)
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
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)
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
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
TCP over BSA Systems (cont’) • Performance
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
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.