Universitat Politecnica` de Catalunya Department of Signal Theory and Communication Radio Communication Group Łukasz Budzisz Stream Control Transmission Protocol (SCTP), a proposal for seamless handover management at the transport layer in heterogeneous wireless networks. Barcelona, 2009 This dissertation investigates and evaluates the idea of handling mobility at the transport layer, using mobile Stream Control Transmission Protocol (mSCTP) as an example of a handover transport layer protocol. To this end, (the first part of) this thesis provides the reader with a necessary background for IP mobility-related aspects, surveying detailedly the most popular of the existing solutions. Provided overview includes Mobile IP (MIP) and its most important derivatives to represent the network- layer-based schemes, as well as Session Initiation Protocol (SIP) as an example of an application- layer approach. The details of the most important transport layer solutions are given on continua- tion, along with the motivation for the development of such mobility management schemes. Among presented transport-layer approaches, the one based on the mSCTP is chosen as a representative for the analysis performed in this dissertation. This choice is additionally motivated by two inter- esting features that SCTP protocol introduces, and that are interesting in the context of handover applications: multihoming and multistreaming (to some extent). (Still in the introductory part) a detailed state-of-the-art of the SCTP protocol is provided, stress- ing its signaling background and original scope of use that did not consider mobility related ap- plication. The described transition from the signaling to a general purpose transport protocol illus- trates the dynamics of the development of this relatively recent proposal, and explains why SCTP is currently one of the most interesting innovative transport protocols. The core of this dissertation outlines major mobility-related considerations in the context of fu- ture heterogeneous wireless networks, identifying all important handover scenarios, and specifying the most representative one to conduct the proposed analysis. Several transport-layer handover schemes based on SCTP are analyzed in the selected scenario. First of the discussed schemes, pro- vided also as a reference model for evaluations presented in the following sections of this work, reuses the standard SCTP failover, a mechanism originally devised to increase protocol robustness. Next, the details of transport-layer loadsharing are explained, to facilitate the introduction of the mSCTP-CMT-PF handover scheme, an essential improvement for transport layer mobility suggested by this work. The devised proposal incorporates one of the most popular loadsharing schemes pro- vided for SCTP, the Concurrent Multipath Transfer (CMT), that originally does not target wireless networks. Evaluation exposes the main challenges of such a design, pointing out the most important constraints limiting its scope of application. Finally, a quantitative comparison of all identified mSCTP-based handover schemes and two of the most representative network-layer solutions is given in a series of analysis that involves mobility models of different grade of complexity. Universitat Politecnica` de Catalunya Department of Signal Theory and Communication Radio Communication Group PhDThesis Stream Control Transmission Protocol (SCTP), a proposal for seamless handover management at the transport layer in heterogeneous wireless networks. by Łukasz Budzisz Barcelona, 2009 °c 2009 Łukasz Budzisz All Rights Reserved Contents 1 Introduction 1 1.1 Problem statement ....................................... 1 1.2 Motivation ............................................ 3 2 Mobility management 5 2.1 Definitions ............................................ 5 2.2 Approaches to mobility management ............................ 8 2.2.1 Sub-network layer mobility issues .......................... 8 2.2.2 Network-layer schemes ................................ 8 2.2.3 Transport-layer schemes ................................ 11 2.2.4 Application-layer schemes ............................... 14 2.3 Conclusions ........................................... 15 3 SCTP for transport-layer mobility 17 3.1 SCTP overview ......................................... 17 3.1.1 Protocol basics ..................................... 18 3.1.2 New protocol features ................................. 23 3.1.3 Protocol extensions ................................... 24 3.1.4 Summary ........................................ 25 3.2 SCTP state of the art in research ............................... 25 3.2.1 Taxonomy ........................................ 25 3.2.2 SCTP research analysis ................................ 30 3.3 Mobility implications ...................................... 34 3.3.1 Related work ...................................... 37 3.3.2 mSCTP use cases .................................... 39 3.4 Conclusions ........................................... 49 4 Failover as a basic handover scheme 51 4.1 Description of the SCTP failover mechanism ........................ 51 4.2 Reference study: analytical estimation of failover time .................. 54 4.2.1 Best-worst case analysis ................................ 56 4.2.2 Estimation example .................................. 56 4.2.3 Estimation verification ................................. 59 4.3 Failover as a basic mechanism to provide mobility ..................... 61 4.3.1 Main parameters .................................... 61 4.3.2 Performance evaluation ................................ 71 4.4 Conclusions ........................................... 80 5 Improving handover with transport-layer loadsharing 83 5.1 Related work on transport-layer loadsharing with SCTP ................. 83 5.1.1 Concurrent multipath transfer ............................ 84 5.1.2 Scheduling algorithms ................................. 85 5.1.3 Taxonomy ........................................ 85 5.2 CMT to improve transport layer mobility: the mSCTP-CMT scheme .......... 86 i 5.2.1 Scenario description .................................. 86 5.2.2 Analytical model .................................... 89 5.2.3 Basic performance evaluation ............................. 90 5.2.4 Extended performance evaluation .......................... 101 5.3 Future work ........................................... 107 5.3.1 ABC in slow start .................................... 107 5.3.2 More frequent link probing schemes ......................... 108 5.4 Conclusions ........................................... 108 6 Extended mobility analysis 109 6.1 Preeliminaries .......................................... 110 6.1.1 Scenario description .................................. 110 6.1.2 Analyzed handover schemes ............................. 110 6.1.3 Simulation parameters ................................. 113 6.2 Analysis results ......................................... 115 6.2.1 Simple scenario (n = 1) ................................. 115 6.2.2 More complex mobility pattern (n = 3) - part 1 ................... 117 6.2.3 More complex mobility pattern (n = 3) - part 2 ................... 122 6.3 Conclusions ........................................... 122 7 Conclusions 129 7.1 Summary ............................................. 129 7.2 Most important remarks .................................... 130 7.3 Future work ........................................... 130 A SCTP support in ns-2 simulator 133 A.1 Introduction ........................................... 133 A.2 Implementation details ..................................... 135 A.2.1 SCTP module ...................................... 135 A.2.2 State of the art for wireless environments and mobility support in ns-2 .... 137 A.2.3 Multihoming in wireless scenarios .......................... 139 A.2.4 Proposed solution ................................... 140 A.3 List of the modified files .................................... 142 Bibliography 143 Index 152 ii List of Figures 1.1 Heterogeneous RANs scenario. ................................ 2 1.2 Dissertation scheme. ...................................... 3 2.1 Mobility scenario. ........................................ 5 2.2 Mobile IPv4 architecture and operations. .......................... 9 2.3 Mobile IPv6 architecture and operations. .......................... 10 2.4 mSCTP architecture and operations. ............................. 13 2.5 SIP architecture and operations. ............................... 14 3.1 SCTP PDU structure. ...................................... 18 3.2 Chunk details. .......................................... 18 3.3 SCTP association setup. .................................... 20 3.4 SCTP association release. .................................... 21 3.5 SCTP multihoming. ....................................... 23 3.6 SCTP multistreaming. ..................................... 24 3.7 Graphical illustration of proposed taxonomy. ........................ 27 3.8 Annual distribution of all published articles. ........................ 31 3.9 Number of articles within each category. .......................... 32 3.10 Annual distribution of all articles within each dimension. ................ 35 3.11 Scatter plot of all handover-related articles. ......................... 38 3.12 Scenario A – The IP address is not changed in the handover process. .......... 40 3.13 Scenario B – Single-homed MN. ............................... 40 3.14 mSCTP handover signaling for a single-homed MN. ..................