1

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

2

Outline

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

3

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

4

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

5

Introduction (cont’)

BSA system configuration

6

Introduction (cont’)

Example (Digital Video Broadcast: DVB-RCS)

7

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

8

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.

9

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

10

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

11

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

12

Objective (method 2 vs. method 3)

13

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.

14

IP-Based BSA Systems (cont’)

User Traffic Protocol Stack

15

IP-Based BSA Systems (cont’)

T1, T2 handles DiffServ Packet

16

IP-Based BSA Systems (cont’)

Simplified drawing of DiffServ Implementation

17

IP-Based BSA Systems (cont’)

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

18

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

19

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)

20

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

21

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

22

TCP over BSA Systems (cont’)

Performance

23

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

24

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.

25

Question?