主動延遲控制 (Active Delay Control) 是我們所提出的一個新的控制傳輸協定 (Transmission Control Protocol (TCP)) 的改良方法，我們在端點 (endpoints) 延遲封包的傳輸以改善 TCP 的效能。延遲的時間多寡可以由路由器依據擁塞程度或者由端點依據所收到的擁塞信號來作決定。在多條 TCP 搶用一條有限頻_的線時，Active Delay Control 可以將這些 TCP 的傳輸速率有效降低，不會像現在的 TCP 一樣造成很多的 timeout。所以 Active Delay Control 對一些生命週期很長而且不能忍受 timeout的 TCP 應用，如影像串流 (video streaming) 和儲存網路 (storage network) 是很有用的。此外，對一些生命週期較短，而且需要很快有效傳輸的 TCP 應用，如 HTTP，Active Delay Control也是很有用的。我們在本文中說明 Active Delay Control 的源由與概念，並藉由模擬分析其效能。

Active Delay Control is a novel extension for TCP, where TCP
endpoints impose delays on the transmission of packets to improve
TCP's performance. The amount of delay can be calculated by
routers based on the level of congestion, or by endpoints based
on the received congestion signal. When there are many TCP flows
competing for the bandwidth of a link, Active Delay Control
mechanism can reduce their transmission rates to arbitrary degrees
by increasing delays, without experiencing timeouts as in today's
TCP. This mechanism is useful for those long-lived TCP-based
applications that can not tolerate timeouts including video
streaming and storage networks. This mechanism is also useful for
short-lived flows that require short transfer time, such as HTTP
transactions. This thesis presents the concept and motivation
behind Active Delay Control and performs analysis and
simulations.

1 Introduction 1
2 Review of TCP and Related Mechanisms 3
2.1 TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Congestion Window . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Slow Start . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 Congestion Avoidance . . . . . . . . . . . . . . . . . . . . 7
2.1.4 Fast Retransmit . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.5 Fast Recovery . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.6 TCP Variants . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Queue Management Mechanisms . . . . . . . . . . . . . . . . . . 10
2.3 More on Many-flow Problem and Related Work . . . . . . . . . . 13
3 Concepts and Mechanisms of Active Delay Control 15
3.1 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Evaluation of Basic Concept 18
4.1 Simulation Environment . . . . . . . . . . . . . . . . . . . . . . . 18
4.2 Number of Timeouts as a Function of Propagation Delay . . . . 20
4.3 Number of Timeouts as a Function of Router Queue Size . . . . 22
4.4 Performance Improvement of Delay Control at Endpoints . . . . 25
5 Receive-Based Delay Control 28
5.1 RDC Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.1 Exact RDC . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.2 Properties of Exact RDC . . . . . . . . . . . . . . . . . . 32
5.1.3 1-bit RDC . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 Simple Simulation for RDC . . . . . . . . . . . . . . . . . . . . . 36
6 Streaming Video over RDC 40
6.1 Layered Video Streaming . . . . . . . . . . . . . . . . . . . . . . 41
6.1.1 Hierarchically-encoded Layered Video . . . . . . . . . . . 41
6.1.2 Use of TCP as the Transport Protocol . . . . . . . . . . . 41
6.1.3 Video Source Streaming Algorithm . . . . . . . . . . . . . 42
6.2 Simulations of Video Streaming . . . . . . . . . . . . . . . . . . . 44
6.2.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . 45
6.2.2 10-Stream Simulation . . . . . . . . . . . . . . . . . . . . 46
6.2.3 100-Stream Simulation . . . . . . . . . . . . . . . . . . . . 49
6.2.4 Streams with Different Round-trip Times . . . . . . . . . 51
6.2.5 Performance Summary . . . . . . . . . . . . . . . . . . . . 52
6.3 Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7 Sender-Based Delay Control 55
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7.2 Sender-Based Delay Control . . . . . . . . . . . . . . . . . . . . . 57
7.2.1 Two-phase Control for SDC . . . . . . . . . . . . . . . . . 58
7.2.2 SDC Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 61
7.3 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.3.1 Number of Timeouts . . . . . . . . . . . . . . . . . . . . . 64
7.3.2 Number of Packet Drops . . . . . . . . . . . . . . . . . . . 65
7.3.3 Packet Delivery Latency . . . . . . . . . . . . . . . . . . . 66
7.3.4 Reducing Bias Against Long RTT . . . . . . . . . . . . . 68
7.3.5 Bandwidth Competition with Traditional TCP . . . . . . 69
7.3.6 Enhancement via the Use of AVQ . . . . . . . . . . . . . 70
8 Conclusions 73

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