Evaluation of an Information Service for enhancedMultiaccess Media Delivery

Jukka Mäkelä, Markus Luoto, Tiia Sutinen, Kostas PentikousisVTT Technical Research Centre of Finland

PO Box 1100, FI-90571Oulu, Finland

firstname.lastname@vtt.fi

ABSTRACTMultimedia delivery in mobile multiaccess network environ-ments is gaining traction as a key area within the futureInternet research domain. When network heterogeneity iscoupled with the proliferation of multiaccess capabilities ofmobile handheld devices, one can expect new avenues for thedevelopment of novel services and applications. In particu-lar, novel mechanisms for audio/video delivery over multiac-cess networks may prove to be a major disruptive technol-ogy. In this paper we present and evaluate a distributedinformation service, which can be used ton enhance me-dia delivery over multiaccess networks. After describing theinformation service, which is built upon the mobility trig-gering framework (TRG) and the distributed control andmanagement framework (DCMF), we introduce our testbedwhich includes 3G/HSPA, WLAN and WiMAX network ac-cesses. We present results that demonstrate the value of theproposed information service in enhancing video delivery inpractice by minimizing service disruption in an involved sce-nario. Finally, we conclude the paper outlining future workitems.

KeywordsMobility management, multiaccess, event service, Informa-tion Service

1. INTRODUCTIONHeterogeneous network environments and multiaccess ca-

pability obviously create new opportunities, but also chal-lenges for applications. Especially for Quality of Service(QoS) sensitive multimedia applications, it is difficult tofully utilize the potential of multiaccess networks as host mo-bility and resulting handovers introduce harmful variabilityto the QoS characteristics of the underlying network con-nection. It is also difficult for the applications to introducesufficient corrective measures (e.g. adaptation) to cope withthe handover-induced QoS changes as the current L2/L3 mo-bility solutions hide mobility completely from higher layers.

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Moreover, in many cases, the handover decision-making ofcurrent mobility protocols is suboptimal for multimedia ap-plications as the decisions are solely based on lower layerinformation (e.g. RSS measurements) and do not take intoaccount the applications’ requirements for network access.

Mobility management in a heterogeneous network needssupport from mobility protocols like Mobile IP [1] or HostIdentity Protocol [2]. These protocols provide one key mech-anism of the mobility management, also in other than IP-networks, handover management, that provides the meansfor changing the point of network attachment. The changeof the point of attachment is usually based on a decisionmade by the mobility protocols or by a separate entity guid-ing the protocols [7]. This decision is based on the con-ditions prevailing in the terminal and/or the network side.More specifically, the decision is triggered by an event orevents created within the system as a response to a changein the conditions. Typically, a change in the received signalstrength, access network availability or user preferences areevents leading to handover decisions.

Since conditions are changing both in the terminal’s andthe networks’ side, distributed decision-making is needed forthe handover management. For enabling these distributedactions, there is a need for a framework to exchange infor-mation between various entities that may be located on thedifferent layers of the protocol stack and in different net-work nodes. Our approach is to use a distributed informa-tion service for collecting and distributing events created bycondition changes in the different parts of the system.

The triggering functionality (TRG) and Distributeed Con-rol and Management Framework (DCMF) proposed in thispaper provide the required cross-layer signalling mechanismsto enable application-aware handover decision-making andenhanced application adaptation in the presence of hetero-geneous handovers. First of all, a multimedia application iscapable of informing the handover manager about its QoSrequirements (bandwidth, delay, etc.). This information canbe collected, for example, from application-layer session de-scriptors (Session Description Protocol) and communicatedto the handover manager via TRG. The handover managercan then map this information to that received from lowerlayers (e.g. MIH) and from the network to select the bestpossible access for the multimedia transmission.

In this paper, we concentrate on evaluating and validat-ing our mechanisms for the information service to show notonly that we have an implementation of these kind of mech-anisms already available but also to demonstrate the per-formance benefits achieved in a mobile multiacces test case.

For the case evaluation, we have created a real heterogeneousmultiaccess testbed environment with 3G/HSPA, WLAN,WiMAX access technologies. The benefits obtained fromusing our information service is validated in the context ofchanging the point of attachment between the different ac-cess networks of the testbed environment.

The rest of the paper is structured as follows. SectionII describes the main concepts of our information system.Section III describes the experimental study scenario andshows the evaluation cases with results. Section IV describesthe related work and finally, section V concludes the paper.

2. INFORMATION SYSTEM CONCEPTIn our previous work [3],visited also in the next subsection,

we presented the main concepts and principles that shouldsteer the operation of general framework suitable for multi-access mobility management . At the core of this frameworklies the Triggering functional entity (TRG) which is capa-ble of collecting, storing temporarily, and delivering notifi-cations called triggers within an IP-based communicationssystem. Triggers signal a change in the system status andthey may originate from virtually any entity that influencesnode communication. This is in contrast with IEEE 802.21(and proposals solely based on this emerging standard), inwhich events originate solely from the lower layers. On theother hand, similarly with IEEE 802.21, TRG leaves theinterpretation of the information carried in the triggers tothe consumers, which can use the delivered notifications asinput to their own decision-making.

We are interested in developing a scalable and distributedsystem that uses cascaded TRGs to deliver a distributedinformation service between different network nodes. Werecently demonstrated the feasibility of our proposal usingcascaded TRGs for delivering triggers from WLAN accesspoints to a Mobile IP client [4]. Cascaded TRG entities, lo-cated at various network locations and the mobile nodes, canexchange information and collaborate in order to increasethe performance of multiaccess mobile devices. CascadedTRG can capitalize on the availability of IEEE 802.21 [5]MIH entities in the network, as both remote and local MIHEvents can be converted into triggers. As explained in [10],the mechanisms and services introduced by recently finalizedIEEE standard are not sufficient for handover triggering anddecision processes. IEEE 802.21 provides a way to commandand use the lower layer information to enable seamless han-dovers and multiaccess, but it does not provide a way to usealso upper layer information like user or application prefer-ences as the TRG framework does. That is why we proposethat instead of using only the services provided by 802.21the system should use TRG framework together with 802.21services. 802.21 can be for example the source entity thatprovides the lower layer information for TRG framework.

Most of the current application adaptation solutions relyon client feedback to make dynamic adaptation decisions(e.g. adjustments to bit rate, frame rate or resolution in thecase of a video streaming application) in the server or someintermediate media-aware network node. The feedback forRTP/UDP-based multimedia applications is typically real-ized using RTCP. Through TRG and DCMF, an adaptiveapplication can gain access to more extensive information(e.g. MIH events, MIP or HIP mobility state changes) thatit can use in adapting its operation more efficiently in a mul-tiaccess environment. Cascaded TRGs can potentially be

Table 1: Trigger formatTrigger datamember

Type Description

id integer Trigger identifier, same asproducer identifier. Mapsproducer name to identifier.

type integer Specific to the trigger iden-tifier. Mapping producer in-formation to type.

value std:string specific to trigger type.timestamp time t Time that a trigger enters

the TRG repository.

employed also in end-to-end feedback delivery, as describedin [20], in cases where traditional feedback protocols do notsuffice.

TRG can feed the multiaccess mobility management decision-making entities which employ mechanisms such as those pre-sented in [7]. The decision on which interface to use can bedefined as a multiple attribute decision making problem andit can be based on different algorithms like Simple AdditiveWeighting: argmaxiεM

∑nj=1 wjrij and Multiplicative Ex-

ponent Weighting:∏Nj=1 x

wj

ij as detailed in papers [8, 9].These are just couple of example that could be used andthe decision making is out of scope of this paper. Otheradaptive procedures like genetic algorithms for solving thedecision problems are also possible as the design of the deci-sion mechanism allows the flexible use of different algorithmsfor the decision.

2.1 Triggering functional entityTRG functional entity has three major components: event

collection, processing and the trigger repository. Event col-lection receives events from triggering event sources via col-lection interface. Triggers can be created by implementingthe trigger event collection functionality, the event collec-tion interface. Event collection interface allows sources toregister their triggers which makes them available to con-sumers. Implemenation of TRG may have several event col-lectors which are responsible for collecting different typesof events. The trigger repository is designed to store thetriggers. It’s planned to meet the requirements of mobilitymanagement, but can be used to store non-mobility triggersas well. Repository basic primitives include adding, remov-ing, updating, and disseminating triggers in a standardizedformat (Table 1).

The origin of an event source can be a hardware device, asystem component implemented in kernel space, or an appli-cation implemented in user space. For example, each devicedriver could implement its own event collection functional-ity, which would be capable of handling triggering eventsproduced by the specific device only. Event sources can alsobe located in the network such as at active network elementsor at the user’s home network e.g. in the Mobile IP [1]homeagent. TRG implementation can act also as a consumer or aproducer to another TRG located in a different node. Thus,orchestrating the collaboration of, perhaps, several collec-tion entities is needed in order to efficiently gather a largeramount of events.

Having dedicated collectors for different event sources en-ables the use of TRG in different operating systems as well.

The collector can format the events to the format (table 1)that TRG understands and there is no need to modify thecore of TRG functionality; instead the collector can be mod-ified as necessary. This is also one of the key points in thearchitectural design of TRG that enables it to handle cross-layer information by having collectors at different layers asneeded. For example TRG can get similar information re-garding the connectivity in FreeBSD through a collector thatuses Route Socket and in Linux through a similar collectorusing RTnetlink socket.

After events are collected from the producers, they arehanded over to the trigger processing engine which is respon-sible for time-stamping and reformatting triggers (if neces-sary), and assigning them to the appropriate group. Thoseentities called consumers which are interested about certaintriggering events can subscribe by specifying a set of triggers(and, optionally, filtering rules) and are expected to unsub-scribe when they do not wish to receive them any longer.For each consumer subscription, TRG makes sure that fil-ters are grammatically and syntactically correct, and acceptsor rejects the subscription. Basic rules can also be used asbuilding blocks for crafting more sophisticated rules. Moredetail about TRG architecture and functionality as well theperformance evaluation can be found from [3] and [12].

2.2 Distributed information serviceFor this paper we have build an heterogeneous test envi-

ronment and evaluated the distributed way of using TRGcalled, cascaded triggering. Meanwhile we have started todefine and implement a distributed control and managementframework (DCMF) [11] illustrated in Figure 1. Cascaded

Figure 1: illustration of Distributed Control andManagement Framework (DCMF)

TRG functionality, that is evaluated in this paper, whereTRG can act as a producer or a consumer to another TRG,provides the fundamental starting points for DCMF. DCMFwill be build to support information change between oper-ators, access control and different optimizations in the net-work architecture. And as mentioned the basis of this frame-work is cascaded TRG functionality that provides a unifiedsignalling architecture between network nodes, capable ofserving different entities, located either in the network orin the terminals and controlled by different players (termi-nals by the user, network by the service provider). The

Table 2: Triggers provided by TRG frameworkName Description

INTERFACE ADD Network interface added to thelocal machine

INTERFACE REM Network interface removed fromthe local machine

INTERFACE CONN Local network interface gained IPconnectivity

INTERFACE DISC Local network interface lost IPconnectivity

ROUTE ADD Route added to the local routingtable

ROUTE DEL Route removed from the localrouting table

WLAN OPER REM WLAN access point operationalstatus change

WLAN CONG REM WLAN access point congestionstatus change

WLAN QUAL REM WLAN radio interface qualitystatus change

network side elements that would benefit from such a sig-nalling framework include, for example, policy management,network/operator aided mobility management, and resourcemanagement. On the terminal side, mechanisms such as mo-bility management or transport protocol optimization solu-tions need access to extensive amount of information relatedto network access characteristics and roaming.

The information that is made available through DCMF,by using the cascaded TRG functionality as a signalling be-tween nodes, can be used for optimizing network and ter-minal side operations in terms of, for example, applications’Quality of Service (QoS) requirements, energy efficiency, se-curity, and network load balancing. In order to obtain rel-evant information for the decision-making process, we needto rely on, for example, operator policies, QoS measure-ments, and various cross-layer events (e.g. those definedIEEE 802.21). But as mentioned defining the DCMF, thatwill bebefit of cascaded TRG functionality, is part of ongoingwork and future work.

3. TESTBED AND EVALUATIONWe have created a testbed, which includes a 3G/UMTS

cell, two WLAN access points, and one WiMAX cell (seeFig. 2). Using this testbed we show how our TRG frame-work can significantly improve the end-user experience. Theconfiguration consists of three network servers, four accessnetworks to which the mobile router (MR) is connected anda mobile client connected to the MR. For mobility the MRuses Mobile IPv4 (MIP) enhanced with the TRG frameworkand acts as router to the mobile network. The TRG frame-work provides the triggers shown in Table 2 to the MIPclient running on the MR.

The decision logic added to the MIP client uses these trig-gers to evaluate all available networks and steer the MR tochoose the best possible network. In the tests QoSMeT mea-surement tool [6] that is running on the streaming server andthe client was used to measure the one-way QoS character-istics experienced by the video stream from the streamingserver to the stream client. QoSMeT is a QoS measure-

Figure 2: Movement of Mobile Node in heterogeneous environment

ment tool developed by VTT which uses GPS synchroni-sation to enable measuring of one-way QoS characteristicssuch as packet delay or jitter of an end-to-end link. Thevideo used in the experiment was streamed as UDP packetswith the size of 1358 bytes and an average bit rate of 485kb/s.

Fig. 3 illustrates three aspects 1) the delay experiencedby the video stream in our testbed using the help of TRG, 2)the active network for streaming the video, and 3) the het-erogeneous handovers. The MR is initially connected to theWiMAX network (A). The WiMAX network is then discon-nected and the MR makes a handover to WLAN1 network(B). When the WLAN1 network is congested by sendingUDP traffic with a bit rate of 60 Mb/s to a another nodeconnected to it the MR makes a handover to the WLAN2(C). Finally, the WLAN2 network’s transmission power islowered gradually until the MR makes a handover to the 3Gnetwork (D).

Figure 3: Handovers in test scenario

Altough a network card is able to maintain connectionwith an access point packets can still be lost due to low sig-nal strength. To address this the TRG framework providestriggers based on wireless network adapter signal strengths.Figure 4 illustrates a signal strength measurement by an in-formation source in the TRG framework. When the signalstrength drops below the lower threshold set in the infor-mation source it sends a trigger informing interested partiesthat the interface in question is considered to be down due tolow signal strength. Again when the signal strength climbsabove the upper threshold a trigger indicating the interfaceis up is sent. The interface down trigger based on the signalstrength triggers the handover (D) in Figure 3.

Signal strength measurement

60

44

0

10

20

30

40

50

60

70

80

90

100

1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181

Measurement point

Signal strength

Upper threshold

Lower threshold

Figure 4: Signal strengh measurement

The packet delay in the WLAN1 congestion situation ((C)in Fig.3) with the help of TRG is graphed in Figure 5 andwithout the help of TRG in Figure 6. In Figure 5 with thehelp of TRG the packet delay remains constant and only90 packets are lost while the MR makes a handover to the

Figure 5: TRG assisted Handover between twoWLANs

WLAN2. Handover mechanism does not have effect to thepacket loss in this case but the packets are lost because of theWLAN1 network congestion. Visually a person viewing thevideo experieces a small glitch in the video just before thehandover is made. Figure 6 shows the loss of 6238 packetsbefore a handover to the WLAN2 is made by the MR. Thishandover is caused by the MR not being able to updateits binding with its HA because of the congestion. Visuallythis translates to 50 seconds of the video being unintelligibleduring which time only occasional broken frames of the videocan be displayed to a person viewing the video.

Figure 6: Handover between two WLANs withoutassist

The measurements without the help of TRG frameworkwere made using the default settings of the MIP client. Inthis case the most relevant setting being the interval at whichthe MR renews its binding with the HA. The default of thissetting on the used MIP client is 60 seconds. This meansthat the MR’s network connection will be down 30 secondson average in case of a total connection loss or a severe net-work congestion as in the example. This problem can be

dimished by lowering the binding renewal interval but thisalso puts unnecessary strain on the network as the commu-nication between the MR and the HA increases. Still, with aless severe congestion it is possible for the MR to experiencelowered QoS and packet losses indefinitely long periods oftime as long as the MIP client is able to renew its bindingwith HA.

Test case evaluations, as seen from the figures, showedthat there is a clear benefit when using the TRG frameworkto assist mobility management protocols. This evaluationcase and the used implementations are also steps towardsthe media independent and seamless handovers in the mobilewireless world.

4. RELATED WORKUsing the event information gives benefit, for example, to

proactively perform a handover in order to maintain QoSlevels, keep application session continuity during handoverprocesses. We also believe that in heterogeneous networkenvironments several sources of events and context informa-tion should be consulted in order to achieve seamless connec-tivity and develop swift mobility management mechanismslike presented in [15]. Event/notification systems presentedin [16, 17], which introduces mechanisms on how to imple-ment such systems, along with the evaluated event gener-ation cases is very encouraging and complementary to oureffort in defining TRG as a specialized notification systemfor events which originate from the entire protocol stack.Event and notification system like TRG functionality areneeded also for the future internet solution like presentedin [14]

As mentioned, the TRG functionality approach is closeto the 802.21 [5] approach. The scope of the IEEE 802.21standard is to develop a mechanism that provides link layerintelligence and other related network information to upperlayers to optimize handovers between heterogeneous IEEE802 systems and facilitates handovers between IEEE 802and cellular systems. IEEE 802.21 helps with Handover Ini-tiation, Network Selection and Interface Activation. Thepurpose is to enhance the experience of mobile device users.The standard supports handovers for both stationary andmobile users. TRG functionality is designed to provide theway to command and use information from all layers, evenfrom the physical radio inteface. Main target is to defineand implement a distributed framework as discussed in sec-tion 2.2 that supports the event collection and processing,and trigger distribution possibly from hundreds of differentsources. An that’s also why we propose that instead of usingonly 802.21 services the system can consist 802.21 serviceswith TRG functionality as well e.g. TRG can be a distrib-utor of MIH events to all application layer producers.

One important issue, which papers [18,19,21] focuses on,are ordering and time related issues considering the events.Since first of all older event should not overrun the neweror current valid event information. Desing and realizationof the TRG functionality is flexible in a way that it supportdedicated mechanisms to handle the prioritising of eventsor ensuring the trust between different entities, namely con-sumers and producers. in addition to that, TRG has a mech-anism itself for timestamping all events it gets from produc-ers as well handling the registration of producers. TRG alsoprovides a mechanism to filter all unwanted events beforedisseminating them to the consumers. current implementa-

tion provides also a way to have policies to strict the accessto the certain event information just for certain consumers.

5. CONCLUSIONIn this paper we have concentrated to show the perfor-

mance benefits gained from using a network aided infor-mation service to assist handovers in a heterogeneous net-works. Triggering functional entity TRG [3], a main com-ponent of our implemented system, was used to build thedistributed information service system. By using this sys-tem in a real heterogeneous environment with 3G/HSDPA,802.11/WLAN and 802.16/WiMAX access technologies wewere able to proof that our implementation is already suit-able for the real network environment and test result showedthat the there are real benefits gained with this system.

It needs to be noted that despite our target to provideefficient way to handle distributed decisions and informa-tion change within heterogeneous networks and multiaccessterminals this system can be realized to guide the mobile ter-minals within a network consisting of only one access tech-nology as well.

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