SEAMLESS HANDOVER AMONG HETEROGENEOUS MOBILE .
View metadata, citation and similar papers at core.ac.ukbrought to you byCOREprovided by ScholarBank@NUSSEAMLESS HANDOVER AMONG HETEROGENEOUSMOBILE NETWORKS USING STREAM CONTROLTRANSMISSION PROTOCOL (SCTP)ENG SE-HSIENG(B.Eng (Hons), NUS)A THESIS SUBMITTEDFOR THE DEGREE OF MASTER OF ENGINEERINGDEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERINGNATIONAL UNIVERSITY OF SINGAPORE2003
AcknowledgmentsThe research work presented herein has benefited from the generous supportaccorded to it by my supervisor, A/Prof Hari K Garg and the Department of Electricaland Computer of Engineering of NUS.Mr. Cyrille Colin, a fellow MEng candidate, has taken part in countlessbrainstorming sessions and has been an invaluable partner throughout the course ofthis work.The developers of the Stream Control Transmission Protocol, Mobile StreamControl Transmission Protocol and the Linux kernel development project have beenextremely patient and responsive to my queries. Even though we have never met, thediscussions we have exchanged have given me a greater understanding of the issuessurrounding transport protocol development.I am grateful to Mr. Eric Siow Hong Lin of the ECE-I2R Laboratory forWireless Communications for his assistance in procuring the necessary equipment forthis project.Last but not least, I thank my family, especially my late father, for theirenduring love and understanding.i
Table of ContentsACKNOWLEDGMENTS . ISUMMARY . VILIST OF ABBREVIATIONS . VIILIST OF FIGURES .IXCHAPTER 1INTRODUCTION . 11.1BACKGROUND . 11.2MAIN CONTRIBUTIONS . 41.3ORGANIZATION OF THE THESIS. 5CHAPTER 2A BRIEF REVIEW OF SCTP . 62.1BIRTH OF SCTP . 62.2SCTP IN WIRELESS ENVIRONMENTS . 62.3ASSOCIATION INITIALIZATION . 82.4MANAGING MULTIPLE ADDRESSES WITHIN AN ASSOCIATION . 102.4.12.5Dynamic Address Reconfiguration (ASCONF) . 11TERMINATION OF AN ASSOCIATION . 13CHAPTER 3LITERATURE REVIEW . 153.1INTRODUCTION . 153.2LINK-LAYER MOBILITY . 153.3NETWORK LAYER MOBILITY . 163.4TRANSPORT LAYER MOBILITY . 163.4.1Datagram Congestion Control Protocol (DCCP) . 17ii
3.4.2CHAPTER 4Mobile SCTP (mSCTP) . 17CRITICAL WEAKNESSES OF SCTP IN WIRELESS NETWORKS . 194.1INTRODUCTION . 194.2SCTP AND NETWORK ADDRESS TRANSLATOR (NAT) TRAVERSAL . 194.2.1Network Address Translation . 214.2.2Port Translation. 254.3FAULT RESILIENCE IN ASYMMETRIC MULTI-HOMING TOPOLOGIES . 264.4SUMMARY OF PROBLEM STATEMENT. 30CHAPTER 5EXPERIMENTAL SCENARIO . 325.1INTRODUCTION . 325.2WIRELESS MULTI-HOMED TESTBED . 325.3CHOICE OF SCTP IMPLEMENTATION . 355.3.1Linux Kernel SCTP (lksctp) . 355.3.2SCTP Userspace Implementation by University of Essen, University ofApplied Sciences (Germany) and Siemens AG . 355.3.3SCTP Reference Implementation . 365.4UDP ENCAPSULATION . 365.5SUMMARY . 38CHAPTER 6PROPOSED ENHANCEMENTS TO SCTP AND ASCONF. 406.1INTRODUCTION . 406.2DEFINITION OF AN ENDPOINT . 406.3ASSOCIATION INITIALIZATION FOR MOBILE HOSTS BEHIND NATS . 426.4DYNAMIC ADDRESS RECONFIGURATION (ASCONF) FOR MOBILE HOSTS. 446.4.1Dynamic addition of an address (ADDIP). 45iii
6.4.2Dynamic deletion of an address (DELIP). 506.4.3Setting of remote primary address (SET REMOTE PRIMARY) . 526.5APPLICABILITY TO HOSTS IN WIRED NETWORKS . 546.5.1A special case when a network interface changes its IP address . 546.6SOURCE ADDRESS SELECTION . 556.7SUMMARY . 58CHAPTER 7ACHIEVING SEAMLESS HANDOVER AMONG WLAN AND GPRS. 607.1INTRODUCTION . 607.2SEAMLESS SESSION HANDOVER BETWEEN WLAN AND GPRS. 607.2.1Test area. 637.2.2Threshold values . 647.3EXPERIMENTAL RESULTS . 647.3.1Packet loss and retransmission. 677.3.2Variation of WLAN RSSI. 677.3.3Instantaneous throughput . 677.4IMPORTANCE AND IMPLICATIONS . 68CHAPTER 8ELIMINATION OF SINGLE POINT OF FAILURE IN ASYMMETRICNETWORKS USING SOURCE ADDRESS SELECTION . 708.1INTRODUCTION . 708.2SELECTIVE ACKNOWLEDGMENT (SACK) CHUNKS . 708.3EXPERIMENTAL SCENARIO . 708.4RESULTS . 728.5APPLICABILITY TO HEARTBEAT CHUNKS . 738.6IMPORTANCE AND IMPLICATIONS . 73iv
CHAPTER 9CONCLUSION AND FUTURE DIRECTIONS . 749.1CONCLUSIONS . 749.2FUTURE DIRECTIONS. 769.2.1One-time authentication. 769.2.2Enabling mobility management in existing applications . 779.2.3Implications of IPv6. 779.2.4Load sharing and load balancing . 78REFERENCES . 79v
SummaryThis dissertation focuses on the development of a transport-layer mobilitymanagement solution using Stream Control Transport Protocol (SCTP), a transportprotocol that is being adopted for general data transport by the Internet EngineeringTask Force (IETF). SCTP supports multi-homing and allows endpoints to use multipleheterogeneous links in an association. An enhancement known as the dynamic addressreconfiguration extension (ASCONF) defines procedures to gracefully add and removenetwork addresses from an active connection without the need to restart the connection.These advantages over traditional TCP make SCTP a promising candidate for transportlayer mobility management in networks.This work establishes key weaknesses of SCTP impeding its deployment.Network Address Translator (NAT) traversal issues have yet to be adequately resolvedand SCTP suffers from poor fault resilience in asymmetric multi-homed topologies.To address these issues, modifications to the protocol were designed, implemented andextensively tested in the course of the research work reported herein.The key benefits of the proposed modifications lie in the fact that SCTP wouldbe fully compatible with IPv4 networks. Any alterations are kept to a minimum anddo not contradict protocol specifications. Most importantly, mobile hosts may makeuse of the modified SCTP to seamlessly roam between heterogeneous networks.Seamless handover between WLAN and GPRS based on SCTP is demonstratedusing an application that is developed and tested on existing commercial networks.This establishes that with the proposed modifications in place, SCTP may be easilysupported by existing heterogeneous wireless network architectures.vi
List of AbbreviationsADDIPDynamic addition of IP address to a SCTP associationALGApplication Layer GatewayASCONFDynamic address reconfiguration extension for SCTPASCONF-ACKASCONF acknowledgmentDELIPDynamic deletion of IP address to a SCTP associationFTPFile Transfer ProtocolGPRSGeneral Packet Radio ServiceI-DInternet-DraftIETFInternet Engineering Task ForceIESGInternet Engineering Steering GroupINITInitialization of a SCTP associationINIT-ACKInitialization acknowledgment of a SCTP associationIPInternet ProtocolLANLocal Area NetworkMTPMessage Transfer PartNATNetwork Address TranslatorOOTBOut-of-the-BluePCMCIAPersonal Computer Memory Card International AssociationPDAPersonal Digital AssistantRFCRequest For CommentsSCTPStream Control Transmission ProtocolSETREMPRISetting of remote primary IP address in a SCTP associationvii
SIGTRANSignaling Transport Working GroupTCPTransmission Control ProtocolTSVWGTransport Area Working GroupUDPUser Datagram ProtocolUSBUniversal Serial BusWCDMAWideband Code Division Multiple AccessWLANIEEE 802.11 Wireless Local Area Networkviii
List of FiguresFigure 2.1 Basic structure of an INIT chunk . 9Figure 2.2 Basic structure of an INIT-ACK chunk. 9Figure 2.3 Basic Structure of an ASCONF chunk. 11Figure 2.4 Parameter embedded within ASCONF chunk. 12Figure 2.5 Basic structure of an ASCONF-ACK chunk. 12Figure 4.1 Basic structure of a data packet . 20Figure 4.2 Function of Network Address Translator . 20Figure 4.3 Leakage of private network address during SCTP association initializationby multi-homed host . 22Figure 4.4 Restricting a multi-homed host to using only one interface. 23Figure 4.5 Leakage of private network addresses during address reconfiguration. 24Figure 4.6 Symmetric two-two topology . 26Figure 4.7 Path diversity in a symmetric two-two topology. 26Figure 4.8 Asymmetric two-one topology . 27Figure 4.9 HEARTBEAT mechanism in two-one topology. 28Figure 4.10 Assignment of a second network address to single-homed Endpoint B . 29Figure 5.1. Experimental network configuration. 32Figure 5.2 Mobile client with Nokia D211 GPRS PCMCIA modem (left) and LinksysUSB WLAN network adaptor (right) . 33Figure 5.3 Existing GPRS and WLAN networks used in experiments . 34Figure 5.4 Basic structure of a UDP-encapsulated SCTP packet . 37Figure 5.5 De-encapsulation of a UDP-encapsulated SCTP packet upon packetreception. 38ix
Figure 6.1 Multi-homed client and server with fixed public IP addresses . 41Figure 6.2 Multi-homed mobile client with private IPs. 42Figure 6.3 Initializing an association from behind a NAT . 44Figure 6.4 Proposed addition of a network address without leakage of private networkaddresses . 46Figure 6.5 Address parameter replaced by Association Key in chunk header of firstASCONF chunk during dynamic addition. 47Figure 6.6 Request Parameter embedded within first ASCONF chunk in dynamicaddition process . 47Figure 6.7 ASCONF-ACK chunk. 48Figure 6.8 Second ASCONF chunk in dynamic addition process. 48Figure 6.9 Request Parameter within second ASCONF chunk in dynamic additionprocess. 49Figure 6.10 Proposed deletion of a private network address . 51Figure 6.11 ASCONF chunk with DELIP request parameter. 51Figure 6.12 Setting a network interface with a private network address as the primarydestination for receiving packets . 53Figure 6.13 ASCONF chunk with SET REMOTE PRIMARY request parameter . 53Figure 6.14 sendmsg() and recvmsg() . 56Figure 6.15 IP PKTINFO ancillary data to specify the outgoing interface . 57Figure 7.1 Flowchart of mobility management application. 62Figure 7.2 Accessing M1 GPRS network and Singtel WLAN outside Delifrance . 63Figure 7.3 Address reconfiguration and mobility management during a file transfer. 66Figure 8.1 Data acknowledgment (SACK) chunks from default WLAN interface. 71Figure 8.2 Packets acknowledged from interface that last received packets . 72x
Chapter 1Introduction1.1 BackgroundWith the increasing trend of wireless network technologies, end-users arelooking to move easily from place to place while retaining access to network services.While cellular technologies meet this demand, they traditionally offer low data rates,such as 21.4kbps or less in GPRS networks [1]. Although 3G cellular networks cansupport an aggregated high speed up to 2Mbps for indoor/small cell environment or384kbps for wide area [2], voice remains the major revenue-generating source andmost bandwidth will be reserved for voice users. For high-speed wireless connectivity,users are now looking to the IEEE 802.11 Wireless Local Area Network (WLAN).WLAN is designed as an extension to wired Local Area Networks (LAN) andoffers a data rate of up to 11Mbps. Since its release in 1999, 802.11b [3] WLAN hasbeen widely deployed in offices, educational institutions, homes and public hotspotssuch as cafes, hotels and airports. WLAN network adaptors are now available asPersonal Computer Memory Card International Association (PCMCIA) cards andUniversal Serial Bus (USB) adaptors for laptops as well as CompactFlash cards forPersonal Digital Assistants (PDA). However, a serious disadvantage of WLAN is itslimited coverage. For example, in the National University of Singapore (NUS), usersneed to be within 60 meters of a WLAN access point.As mobile end-users enter the coverage area of each network, they will belooking to access network services anywhere, anytime. With cellular technologies asan always-on backup, users may wish to pop into the nearest hotspot or use the waitingtime in an airport to perform data-intensive tasks on the WLAN backbone.1
Personal mobility [4] enables a person to access services irrespective of hislocation and the terminal he is using. For example, a user may possess both a GPRScellular phone and a WLAN-enabled PDA.However, the convergence of PDAs andcellular phones, as well as the increasing portability of tablet PCs and laptops, implythat users will be able to access both cellular and WLAN technologies on the samedevice. Terminal mobility enables devices to receive continued access to services,independently of their location and while moving. This thesis focuses on enablingterminal mobility.Devices which have multiple network interfaces and IP addresses are termed“multi-homed”. The Stream Control Transmission Protocol (SCTP) [5][6] from theInternet Engineering Task Force (IETF) supports multi-homing and allows hosts toinclude several IP addresses in a connection. SCTP was originally designed by IETFfor signalling networks. However, it has since been elevated to stand beside UDP andTCP as a general-purpose transport protocol.It is a secure, connection-orientedprotocol that supports multi-homing and multiple streams, making it particularly suitedfor wireless environments [7] [8].Multi-homing allows a network session to be more resistant to network failure,which would cause a singly-homed host to be temporarily unreachable. SCTP furtherallows the endpoint to securely and efficiently migrate sessions from one network linkto another, providing a means for reliable failover recovery.With the DynamicAddress Reconfiguration (ASCONF) extension [9], SCTP endpoints can even modifythe list of network addresses and select the primary network interface for receivingpackets. Unlike traditional TCP, the connection does not need to be restarted to switchfrom one link to another. SCTP thus provides the potential for mobile hosts to enjoyseamless handover between heterogeneous networks.2
Mobility management may be defined in broad terms as the ability to keeptrack of a mobile host’s movements [10]. This may be achieved in several ways.Cellular technologies and WLAN support mobility within their respective technologiesand this is known as link-layer mobility. Network-layer mobility solutions, such asMobile IP [11], are routing-based approaches that allow devices to be reached at theiroriginal network addresses even when they are in foreign networks. However, thedeployment of Mobile IP would require substantial changes to IP architecture.Transport layer mobility management [12] allows mobile hosts to roam seamlesslybetween heterogeneous networks, using link-layer information to track the presence oflinks. This requires support from end-hosts and applications but requires no change tothe IP substrate and may be easier to deploy. With SCTP’s support for multi-homing,SCTP has been identified as a transport protocol that can lead to a transport-layermobility management solution.The objective of this work is to examine the feasibility of SCTP as a transportlayer mobility management solution in mobile networks. The critical weakness thatmay hamper the adoption of SCTP and ASCONF in wireless networks is identified asthe lack of a viable Network Address Translators (NAT) traversal solution.Acomplete NAT traversal solution is defined and implemented.It has previously been identified that SCTP provides poor fault resilience inasymmetric multi-homing topologies [5]. Asymmetric multi-homing topologies arisewhen an endpoint has fewer network interfaces than its counterpart, a likely scenariowhen mobile clients with several low-bandwidth links connect to a server with onehigh-speed link. Enhancing SCTP with source address selection would circumventassociation breakdown in asymmetric topologies [13]. In the course of developing the3
NAT traversal solution, a novel and simple method of source address selection forSCTP has been devised.Modifications to the protocol are kept to a minimum.Original protocoldefinitions of SCTP in Request for Comments (RFC) documents are adhered to, withmodifications being proposed only for procedures that are outlined in Internet-Drafts(I-D).The proposed enhancements to SCTP and ASCONF are implemented andextensively tested. To demonstrate seamless handover and mobility management, anapplication is developed to transparently switch between GPRS and WLAN during anactive file transfer. The wireless access technologies used as examples in this thesisare GPRS and WLAN, but the results apply to IP-based networks in general.1.2 Main contributionsThe main contributions of this work are as follows: Establishes critical weaknesses impeding the deployment of the Stream ControlTransmission Protocol (SCTP) and its Dynamic Address Reconfiguration(ASCONF) extension in IPv4 networks Proposes modifications, which have been implemented and tested, to SCTP andASCONF procedures to allow for Network Address Translator (NAT) traversal Enhances SCTP with a source address selection feature that may resolve the singlepoint of failure in asymmetric network topologies. Demonstrates internetworking between existing commercial GPRS and WLANnetworks using the modified SCTP.4
1.3 Organization of the thesisChapter 2 provides background information on SCTP, with an emphasis on itsmulti-homing feature and how it manages network links during a connection. Chapter3 discusses existing transport-layer mobility management solutions and in particular,describes the concept of Mobile SCTP as it has been introduced in existing literature.The challenges facing the deployment of Mobile SCTP are identified inChapter 4. Chapter 5 describes the experimental setup that was subsequently used toimplement and test modifications to SCTP.Chapter 6 presents the proposedenhancements to SCTP, including a complete NAT traversal solution for SCTP thatcovers aspects from association initialization to dynamic address reconfiguration. Theintroduction of a novel feature in SCTP known as source address selection, whichwould improve fault resilience in asymmetric topologies, is also discussed.Theimplementations of a mobility management solution based on the modified SCTP, aswell as the results of the field trials, are presented in Chapter 7. Chapter 8 extends thesource address selection feature to SCTP acknowledgment chunks, eliminating acritical weakness of SCTP known as single point of failure in multi-homing networks.Finally, Chapter 9 concludes this dissertation, with a discussion on future steps tomaximise the mobility experience for the end-user. The program codes and referencesare provided in the accompanying CD.5
Chapter 2A brief review of SCTP2.1 Birth of SCTPThe Stream Control Transmission Protocol (SCTP) was designed by theInternet Engineering Task Force (IETF) Signalling Transport Working Group(SIGTRAN) to replace the lower layers, Message Transfer Part (MTP) 1-3, of the SS7signalling protocol. However, the Internet Engineering Steering Group (IESG) hassince decided that the resulting protocol is robust enough to be elevated from aspecialized transport for telephony signalling to a new general-purpose transportprotocol to stand alongside the User Datagram Protocol (UDP) and the TransmissionControl Protocol (TCP). To this end, SCTP has been moved from SIGTRAN to thegeneral Transport Area Working Group (TSVWG). A detailed description of SCTPcan be found in [5] or RFC 2960 [6].2.2 SCTP in wireless environmentsReliable transport protocols such as TCP have been tuned for traditionalnetworks made up of wired links and stationary hosts. It is well known that TCPperforms well in such networks by adapting to end-to-end delays and packet lossescaused by congestion [14]. It provides reliability by maintaining a running average ofestimated round-trip delay and mean deviation, and by re-transmitting any packetwhose acknowledgment is not received within four times the deviation from theaverage. Due to the relatively low bit-error rates over wired networks, all packetlosses are assumed to be due to congestion alone.6
In the presence of high error rates and intermittent connectivity characteristic ofwireless links however, TCP reacts to packet losses as it would in the wiredenvironment: it drops its transmission window size before retransmitting packets,initiates congestion control or avoidance mechanisms. These measures result in anunnecessary reduction in the link’s bandwidth utilization, thereby causing a significantdegradation in performance in the form of poor throughput and very high interactivedelays [15][16]. Simulation results presented in [17] have shown that the main cause ofTCP performance degradation on a lossy link is indeed the congestion algorithm.SCTP distinguishes itself from TCP by its capacity to maintain multiplestreams of messages inside a single association. Multi-streaming allows the sequenceof messages to be maintained within each stream independently of the others. Insingle-stream transport, if a packet is lost, packets following the lost one will be storedin the receiver’s buffer until the lost packet is retransmitted from the source. This isknown as head-of-line blocking in TCP where only one stream carries data. In SCTP,multiple-stream transport ensures that data from the alternative streams can still bepassed to upper layer applications. According to an article by Sun Microsystems on4G wireless systems [7], this makes SCTP ideally suited for connecting andmonitoring wireless cell phone and Internet appliances.SCTP’s multi-streamingfeature has already been evaluated over satellite links in work supported by NASAwith encouraging results [8].SCTP additionally supports multi-homing. Hosts are able to take advantage ofmultiple network layer addresses belonging to different network interfaces during anassociation. This means that peers are able to make use of logically distinct paths toreach the host. Furthermore, the validity of each address is actively monitored byendpoints which regularly send out message chunks known as HEARTBEATs.7
Failures or losses of sessions during an active association can thus be instantlydetected.SCTP multi-homing capabilities were primarily designed for failover errorresilience. In the case where the primary network address fails, or when the upperlayer application explicitly requests the use of the backup, data is channelled to otheravailable network addresses. This is in contrast to a TCP connection where theendpoints may not change their IP addresses without restarting the connection.The authors of SCTP have further proposed an extension to SCTP known asDynamic Address Reconfiguration (ASCONF) [9]. With this enhancement, hosts areable to constantly update their list of available addresses while on the move. Thismakes SCTP particularly suitable for mobile clients that roam between heterogeneousIP networks, e.g. WLAN and GPRS. The above advantages of SCTP make it apromising candidate for transport-layer mobility management.2.3 Association InitializationAn established connection between two endpoints is known as an association inSCTP terminology.This association is established after a four-way handshakebetween the two endpoints which exchange the following chunks:1. INITThe host sends an INIT chunk requesting an association to its peer. In this chunk, thehost includes a list of its IP addresses that it wishes to include in the association. Thebasic structure of an INIT chunk is shown in Figure 2.1.8
Chunk CodeINITChunk Flags 0x00Chunk LengthInitiation TagAdvertised receive window creditOutbound streamsMaximum inbound streamsInitial Transmission Sequence NumberOptional Parameter #1 (e.g. IP addresses) Optional Parameter #NFigure 2.1 Basic structure of an INIT chunk2.
use of the modified SCTP to seamlessly roam between heterogeneous networks. Seamless handover between WLAN and GPRS based on SCTP is demonstrated using an application that is developed and tested on existing commercial networks. This establishes that with the proposed modifications in place, SCTP may be easily
Handover notes assist following up on issues if necessary. Handover notes help provide a measure of quality of life of the care home resident. Handover notes were crucial in charting a resident's progress and enabling the family of a resident to request a review of a care package (which one participant complained would not occur
6.3 Time 6.4 Place 6.5 Method 6.6 Information that must be included in Handover 6.7 Delegation of duties 7 Consultation 8 Controls and Archiving 9 Implementation and Monitoring 10 Training and Support Appendix A Clinical Division Handover Procedure Template Appendix B Clinical Audit Standards Appendix C Nurse Handover between shifts template
as Archibus and Oracle including asset register requirements. 2.3 RIBA Work Stage 5-6 Construction, Handover and Close Out, Soft Landings Stage 3 Pre-Handover 6-3 months ahead of Handover 2.3.1 Develop and agree handover programme with key end-users, ke
Handover Algorithm Design and Simulation in Heterogeneous Wireless Networks 4 1.3 Problem statement Given the above considerations, it has become paramount that a mobile device connects, at
Handover-Document Brussels 28 November 2011 Content Handover-Document ACARE Presentation at ICAS summarizing the Work of ACARE (Sept. 2010) Executive Summary Strategic Research Agenda 1 (Oct. 2002) . Job Preparation by involvement in industrial European research
Primary Headteacher Handover Checklist Updated June 2018 Emma Hickling It is advisable that, when a headteacher leaves a school, there should be a formal verification and handover of all the key information and financial assets and accounts of the school.
a blinkered manner at the day and date of the handover, but rather promoting the idea of transition. Just as the project phase should not be viewed in isolation, neither should handover. The approach has been a three stage process: 1. A literature study of articles written about project handover to build up a list of assumptions
Jeffery was a good introduction to scoping. In appropriate order different bureaucratic levels were tackled, always sensitive to the pressures in each place. The many discussions with Roger proved useful during the field work later. For example, we confronted the problem of finding very large sample sites which were suitable on other parameters. So we discussed how this should be tackled .
