SAFIRE: A Self-Organizing Architecture forInformation Exchange between First Responders

Nabeel Ahmed, Kamran Jamshaid, and Omar Zia KhanUniversity of Waterloo, Waterloo, Ontario N2L 3G1Email: {n3ahmed, kjamshai, ozkhan} @uwaterloo.ca

Abstract- Disaster response requires quick and timely mobi- Uninterrupted remote connectivitylization of relief efforts to save lives and property. Fundamentalto these efforts is a reliable communications infrastructure that C>allows the disaster response teams to coordinate and exchange c _ _A ' iinformation in an efficient manner. Existing solutions for disaster ALocal m A er _ __-X'"response are inadequate as they suffer from interoperabilityproblems and lack the appropriate amount of flexibility. Inthis paper, we propose SAFIRE, a novel multi-hop architecturefor facilitating fast and reliable information exchange betweenfirst responders. The salient features of SAFIRE are (1) A Main Command Center AEdecentralized cognitive radio-based approach for supportingdirect communication between first responders, (2) A publish- Intermittent connectivitybetween nodes on disaster sitesubscribe mechanism for exchanging information among firstresponders, and (3) A flexible multi-layered policy framework Fig. 1. Localized communication between teams on the ground requires fine-grainedfor optimally configuring the system. We present the challenges crisis information. Main command center, on the other hand, is interested in summarizedin designing SAFIRE, and outline its basic components. We information on relief operations.believe our exploration of such an architecture opens up a set ofunique challenges related to the integration of different systemsto realize SAFIRE, giving rise to new avenues for research In ccommunication systems for disaster response. networks are often unable to handle the necessary traffic

volumes. Teams of first responders may need to communicatewith either the central command center, or with other teams on

I. INTRODUCTION the disaster site. In the first scenario, the long-distance com-

In a typical disaster scenario first responders, emergency munication link with the central command center is typicallyservice teams, and global relief agencies (hereafter collectively established through VSAT terminals that are mounted at se-referred to as first responders) quickly mobilize to aid those lected mobile command centers. In our work, we focus on theaffected by the disaster. The disaster zone can be large and second communication scenario. Specifically, we are interestedgeographically spread apart, as seen in the Indian Ocean in situations where first responders collaborate with each otherTsunami of 2004 and the South Asian Earthquake of 2005. to share information that is useful to other responders alsoUnfortunately, relief operations are often hampered due to operating on the ground or in the air (shown in Figure 1). Thiscommunication and coordination issues between first respon- localized communication paradigm is inherently different fromders. These teams often have to act on partial information the wide-area communication between the disaster site andcollected in some ad hoc and unreliable manner (such as the main command center. While the main command centerthrough news agencies or word of mouth). Also, any local is mostly interested in overall statistics pertaining to reliefinformation collected by a team may not be available to other operations, local networks must exchange more fine-grainedteams in adjoining areas. information on shorter timescales for accurately coordinating

First responders often have to make crucial decisions based relief efforts.on the collected information. Failure to communicate accurate Realizing a disaster response system that encapsulates theand timely information can cost lives - of both first responders information sharing capabilities outlined above is non-trivial.as well as those they are trying to assist. Under these circum- Existing work has attempted to address this problem by astances, first responders can benefit from a reliable commu- variety of techniques. However, a number of fundamentalnications infrastructure that provides the requisite information problems still need to be solved to realize a practical systemin a timely manner. Examples of data that may need to be for disaster response. The following are some of the keyshared include statistics related to human loss or property observations that motivate our work.damage, outbreak of a disease, topographical information of Network Interoperability Limitations: Interoperability ofthe disaster site (e.g via images/video), rising water levels or network devices belonging to first responders is a key require-other weather-related information. ment for coordinating relief efforts. It is a well-known fact that

Existing communications systems fall short of providing the emergency response teams, even within the same municipality,necessary support for these situations. Large disasters destroy have incompatible radio systems, prohibiting coordination of

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relief work [19]. A poignant reminder of this fact is the human . A publish-subscribe system that sits atop a disruption-loss that was associated with the 9-11 disaster. When police tolerant networking substrate. This allows SAFIRE toofficials realized that the south tower of the World Trade Cen- support publish-subscribe functionality even in environ-ter was about to collapse, they immediately issued evacuation ments where end-to-end connectivity is not always avail-orders to their personnel. Unfortunately, this information was able.not available to fire officials at the scene, resulting in the tragic . A policy framework feeding multiple layers of the pro-loss of many of their lives. tocol stack, to allow optimal configuration of the in-

Global harmonization of standards and spectrum for public formation sharing overlay. We propose cross-layeringsafety is difficult. While the U.S. and other developed countries techniques to allow a bottom-up approach to networkare planning to allocate chunks of the soon-to-be-vacant analog configuration.TV bands for public safety purposes [17], these bands will It turns out that the complex inter-coupling between thesecontinue to be used in many developing countries in the SAFIRE components brings forth a set of unique challengesforeseeable future. related to building such a system for disaster response. We

Bootstrapping and Congestion Issues: While use of public present details of these components and list challenges as-safety bands may address interoperability problems for regions sociated with them in this paper. The rest of the paper isunder the jurisdiction of a single regulatory body, they may organized as follows. Section II discusses the requirementsstill suffer from network deployment and performance issues. and challenges that need to be addressed in realizing such aTraditional radio systems require setting up and configuring disaster response system. Sections III and IV provide an archi-the system, which can incur substantial overhead. Moreover, tecture overview and some details on the policy specificationwe can also run into network congestion problems due to mechanism of SAFIRE. Section V discusses related work andlarge network traffic volumes. In its report, the 9-11 Commis- Section VI ends with a conclusion and some directions forsion blamed communication failures partly on simultaneous future work.attempts to use a common tactical radio channel by thousandsof first responders operating at the disaster site [2]. II. CHALLENGES

Intermittently Connected Networks: In a large disaster,relief operations would likely occur in tiny pockets that are In this section, we discuss the requirements and challengesgeographically far. In such scenarios, information sharing faced in establishing an information sharing system for disasterbetween relief workers can be facilitated through the use of response. Interoperability is one key problem that can beinformation relays (e.g., rescue helicopters), that pick up and addressed through the use of cognitive radios. We list furtherdeliver information between relief sites. Although this is akin requirements and challenges below.to an ad hoc network, ad hoc networks typically assume end- . Rapid deployment The communications infrastructureto-end connectivity (direct or multi-hop) between communi- needs to be rapidly deployable. As such, it should be self-cating entities. This may not always be possible when the organizing, and discover other nodes and communicationdisaster site is large and nodes are continuously mobile. Such opportunities without requiring manual intervention. Thisintermittent connectivity places additional constraints on the requires the capability to correctly infer the current con-network architecture, requiring disconnected nodes to buffer text, determine the best sequence of actions, and thendata and opportunistically discover transmission opportunities, react accordingly.as and when they become available. . Adaptable. Network and communication characteristicsMore recently, there has been a surge of interest in de- can vary considerably over the course of the disaster

veloping software reconfigurable radios (also called software- relief operation, and thus cannot be pre-determined. Thisdefined radio, or SDR) that make a radio interface interoper- includes characteristics such as the network topology,able across different standards and network types. Cognitive type and size of exchanged traffic, as well as changingradios [14] are SDRs that dynamically re-tune their radio pa- application service requirements, e.g., the type of datarameters based on feedback they obtain from their surrounding collected can range from aggregate statistics on casualtyenvironment. This functionality can allow the cognitive radio numbers, to images/video content of a specific site.to discover other transmitting nodes in its vicinity, and to self- This necessitates that the communication infrastructureorganize into an information-sharing network, subject to the be flexible enough to accommodate these changing re-policy specifications outlined by its users. quirements without sacrificing system performance or

Based on these observations, SAFIRE makes the following hindering other operational aspects of the network.contributions: . Resilient and Robust. The communication infrastructure

A decentralized cognitive radio based approach that needs to be resilient and robust. This is challengingsupports interoperability, improved performance, and en- as nodes can be highly mobile, resulting in frequenthanced usability for first responders. It allows dynamic disconnections and link failures. As previously described,discovery and formation of networks, with communica- an end-to-end connection may never exist between pairstion characteristics that may be altered on-the-fly to meet of nodes wishing to share information. This imposesthe constraints of a given application. It also reduces setup challenges on both the communication protocols as welland configuration times, thus allowing first responders to as the communications infrastructure. The communica-concentrate on their core tasks. tion protocols need to be designed such that they are

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disruption-tolerant. Similarly, the communications infras-- Xtructure needs to be modified to enable a store-and- ---og---forward approach, whenever disconnections are encoun- Application Layer Pub-Sub Enginetered. - |Application Overlay

O I

Incrementally Deployable. Any feasible replacement for Pub-Sub Modulethe current generation of disaster response communica- -Transport Layertion systems must be incrementally deployable, so as not ------------0-to require a complete overhauling of the existing infras- L Data-centric _ _t_n.

Network Layer. I Itructure. It must also be backwards compatible, where Topo.Gen. Storage

new users can benefit from using the information sharing RoutinglForwarding Modulenetwork, while also having the ability to communicate .t..... Iwith legacy radio systems. MAC sensing RFTuning

* Power conservation. End user devices must be small and -=RF Front Endportable, limiting their battery size. Power conservation Radio Moduleis an important issue as teams of first responders may (a).Standar Network.Stack

(a) Standard NMetworkStack (b) SAFIRE Architectureremain deployed at forward bases for days, or evenweeks.*Multi-layered Policies: Existing policy specification Fig. 2. (a) Illustrates the standard network stack, while (b) illustrates how components

of the SAFIRE architecture map to this stackframeworks for cognitive radios only account for physicallayer information to tune the radio. Their goal is tooptimize use of the RF spectrum. For disaster response, their interests in different types of content, without explicitlywe advocate that these radios create topologies that are listing the source of the data. Updates of published contentconducive to optimizing the operation of the information- are propagated to the respective subscribers, thus decouplingsharing overlay. This necessitates policies that make use the publishing and information delivery process.of higher layer information in order to configure the Given the lack of any single central entity in our system, weunderlying radio. advocate a decentralized implementation of publish-subscribe

. Security and privacy requirements. Depending on ap- functionality in SAFIRE. This design choice naturally leadsplication requirements, network security and data privacy to the publish-subscribe system being implemented atop anrequirements can vary significantly as well. e.g., when application-based overlay, such as a DHT [5] or CAN [18].the network is used primarily for facilitating exchange of The overlay is responsible for establishing communicationstatistical information, data confidentiality (or anonymity) links between participating nodes, which may even result inmight not be particularly required, though maintaining multi-hop routes. Due to this overlay functionality, publishersdata integrity might still be important. However, if the and subscribers can operate without explicitly requiring anynetwork is used to transmit medical files for patients knowledge of the underlying network topology.undergoing treatment, then user authentication and end- It may be noted that publish-subscribe systems allow up-to-end data confidentiality may be needed, as per govern- dates to be disseminated using either a push or pull approachmental regulations (e.g., HIPAA requirements for security [9]. These approaches have different merits based on theand privacy of health data in the U.S. [1]). Balancing current state of the network and subscribers. SAFIRE does notthese security issues against the requirements for timely restrict usage to any particular method of information access,and efficient exchange of information in life-and-death and can be configured to support both push- and pull-basedsituations involves both policy and technical issues that mechanisms.need to be understood. While the pub-sub provides an effective mechanism to

disseminate information, it does not solve naming issues, inIII. DESIGN AND ARCHITECTURE the event that different teams use different naming schemes.

We propose the use of ontologies to mitigate this problem.WAFIREnow comproviet oventrview zhed SFi arlfunchiteclitur Ontologies provide a way to express different concepts thatSAFREisomletlydeentalzed wthallfuctinait are represented in a standard yet decentralized manner. If

residing at the end nodes. A component-based layout of a the .prticipatin amscandar eeentalbasi ontooy fSAFIRE node is illustrated in Figure 2. the participating teams can agree on a basic ontology, fur-

SAFIe nodrcoeisoilustraedn Figuresing2. isarchitecturether extensions can be made by individual teams to supportThe four core components comprising this architecture adiioa doanseii in.forato. Moevr rasainare the Pub-sub module, the Routing/Forwarding engine, theRadio module, and the Policy module. We discuss each of between ontologies can also be made to map between differentthem in tumn, concepts. The working of the pub-sub module is depicted in

Figure 3. We reuse recent work done on combining ontologieswith pub-sub systems so that information is not only properly

A. Pub-Sub Module structured, but also effectively distributed to interested entities

Publish-subscribe systems are a natural fit for our data- [13].centric information sharing network. Data is published by pub- It should be noted that all other components in SAFIRE arelishers without specifying any receivers. Subscribers register configured to optimize the operation of the pub-sub module.

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Responderl Responder2 them for our purpose. It may be noted that the pub-sub modulefunctions without any knowledge of this routing behavior.

OntologyA OntologyA

Publi~sh Pbih_

l//bscribe 0 - Subscribe 0 C. Radio ModuleOverlay Overlay The radio module is responsible for managing the configura-

tion of the cognitive radio. There are two essential componentsResponder3 of this module, a sensing component and a tuning component.

OntologyB: The sensing component performs sensing of the RF spec-\ \ ~~Publish trum to extract usage information on different channels. Spec-

trum sensing is challenging for two reasons. First, the delayinvolved in periodically scanning different channels needs tobe minimized. Second, sensed information might itself beinaccurate, due to short-term variations of the wireless channel

Fig. 3. Responderl and Responder2 subscribe to data from Responder3. Responder3 (e.g. channels undergoing a deep fade). Prior work suggestssubscribes to data published by Responderl. Responderl and Responder2 share the same that coordination among radios can improve sensing accuracyontology (i.e., OntologyA), whereas Responder3 uses a translation from OntologyB to by up to an order of magnitude [4]OntologyA and vice versa. Each pub-sub module sits atop the forwarding/routing, andradio modules as shown in Figure 2. Sensed information is then passed to the tuning component

that subsequently tunes the radio. Traditional radio tuningThis necessitates the need for cross-layer interactions where policies only capture channel specific information such asthe pub-sub module exposes statistics (such as publishing channel utilization and channel quality. We propose extendingfrequency and importance of published information) to lower the policy framework to include policies that specify higher-layers of the protocol stack. These layers then configure layer constraints (through the policy module). Specifyingthemselves based on the provided information and periodically policies in this way makes radio tuning a multi-layered, multi-propagate their state up the stack to the pub-sub module, for objective optimization problem. In Section IV, we illustrate anoverlay optimization. example radio configuration algorithm that uses a given set of

constraints described by higher layers of the protocol stack.

B. Routing/Forwarding Engine

There are three main functions of the routing/forwarding D. Policy Moduleengine. First, it attempts to learn the topology of the SAFIRE The policy module establishes the necessary ground rulesnetwork. Second, it uses the learned topology to decide the that impact the operating characteristics of all other modules.best way to route packets within the network. Third, if an end- These policies are a comprehensive set of scenario-based rules,to-end connection does not exist, it stores packets so that they e.g., policies related to publishing and subscribing to differentmay be forwarded later when a connection opportunistically types of data determine how the pub-sub overlay handlesbecomes available. We describe each of these functions below. requests for shared information (Section III-A). Similarly,

Topology information changes over time due to node mo- policies for the routing/forwarding engine correlate acceptablebility, failure, or reconfiguration of radio parameters. Nodes delay bounds for different packet priorities with the routingemploy a link-state routing protocol to determine the current protocols to be used (Section III-B). Finally, the policy modulenetwork topology, as discussed in [12]. This information is describes how the radio module should tune radio parametersthen made available to the routing/forwarding engine (for based on input from the pub-sub system. Next, we discuss anrouting purposes), as well as the application overlay (to reor- example instantiation of policies for tuning the radio.ganize the overlay based on link availabilities in the underlyingnetwork). IV. RADIO TUNING ALGORITHM

The routing/forwarding engine considers topology informa- We now discuss an example radio tuning algorithm for thetion as well as packet priorities in the routing process. Packet SAFIRE architecture. Instead of espousing an optimal tuningprioritization is useful because situations may occur where algorithm, the goal is to illustrate how multi-objective policiesonly brief windows of opportunistic connections exist between can be incorporated into the radio parameter tuning process.networks. In disaster situations, certain types of content may The algorithm we describe incorporates policy informationbe more crucial than others. e.g., an emergency alert versus from multiple layers of the protocol stack. The policies dic-simply reporting casualty statistics. Defining priority classes tated by the application overlay optimize radio configurationallows the system to push out higher priority data first. During based on the requirements of the pub-sub system (e.g., datarouting, nodes obtain data prioritization primitives as well as priority that may bound the end-to-end delay experiencedthe routing protocol to use from the policy module. on different communication paths). The policies dictated byDue to packet prioritization, the routing/forwarding engine the network layer incorporate information pertaining to the

would buffer packets with lower priority that could not be underlying multi-hop communication network (e.g., requiredtransmitted earlier. As soon as another opportunistic connec- per-node throughput). Channel policies take wireless channeltion becomes available, these buffered packets would then be characteristics into account in the radio parameter tuningsent out. DTNs [10] support such functionality so we employ process (e.g. channel utilization, channel quality, etc).

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Algorithm 1 Multi-Objective Policy Implementation1: ( = ordered array of power levels2: r1 = set of PSD values across RF spectrum

U) ~~~~~~~~~~~~~~3:A =noise threshold on a channel4: 13 = throughput requirement for node being configured

A threshold 5: a = hop threshold6: A =candidate channels47: Cn channel allocated to node

I the sample pseudocode shown in Algorithm 1, thegoal 18: p = transmit power of node9: Populaterj with collected PSD values

10: for i= 1... T do0 1 2 3 4iGhz 11: if Tii<oAthen

12: A = A Uaeb /* Channels with acceptable noise levels 2<Fig. 4. Example of spectral utilization in the 0-4 Ghz range 13: end if

14: end forIn the sample pseudocode shown in Algorithm 1, the goal 15: C =mi(A) 1* Find the lowest frequency in set A*

is to ensure that node throughput requirements are met with 16:p* Start at lowest power *1minimal expended energy. Additional constraints specified17o for i 1... doare the delay requirements, which are in part determined by 18. T =ComputeHopDistance(C, &i)the maximum hop-count between source/destination nodes, 19: 1* Find channel meeting hop threshold requirement *as well as acceptable channel noise levels. The tunable pa- 20: if T <=a thenrameters we consider are the radio's transmit power and its 21 if ComputeBW(C, &i) >= 13 thenfrequency/channel of use. The algorithm assumes that both 22: p = ~i/ Set transmiit power of radio *transmit power and radio channels are discretized. 23: Terminate Algorithm.

The sensing unit in the node first generates a Power Spectral 24 end ifDensity (PSD) map of the radio spectrum, an example of 25: end ifwhich is shown in Figure 4. The node only considers fre- 26: end forquencies/channels having an average noise level less than aspecified threshold A (lines 10-14). These acceptable channelsconstitute elements of set A. The node then finds the channel is obvious. Various governments are taking measures to thiswith the lowest frequency in set A, as this is the channel effect. In the U.S., the Office of Interoperability and Com-which provides the best RF propagation characteristics, and patibility is overseeing such efforts across local, state, andcan therefore give the node the lowest hop count distance federal agencies. The European Union expects to have similaramong all available channels in set A (Min function on line systems in place by the year 2010 [8]. While this may solve15). Starting with the minimum defined power level, the node interoperability issues, scalability concerns still need to bethen attempts to find the first power level that meets the addressed. Public safety bands are still susceptible to networkhop count (or delay) requirements (ComputeHopDistance congestion collapse due to communication overload in thefunction on line 18). If such a power level exists (determined aftermath of a disaster.in line 20), the node determines the available capacity of Most of the current research literature for disaster man-the channel (ComputeBW function on line 21). Note, the agement focuses on establishing some form of multi-hop adcapacity of a channel, as determined by Shannon's Capacity hoc communication network. Interoperability is not explicitlyLimit theorem, is a function of the transmit power used and addressed, though the use of standards-based IEEE 802.11the width of the channel employed during transmission. If radios tries to obviate this problem. Each system only ad-channel capacity requirements are met (based on the node's dresses a point-problem for disaster management (e.g., [6]),throughput requirement), the node assigns itself the given and it is unclear if all the proposed modifications for atransmit power level and the algorithm terminates. Otherwise, particular application will work equally well in all scenarios.the node increases its transmit power by a step (line 17), and The architecture we propose allows cognitive radios to adaptrepeats the process. dynamically as per the application's requirements.

This example algorithm illustrates one way of realizing the There is active research in studying the individual com-configuration of a cognitive radio in the SAFIRE architecture. ponents proposed in SAFIRE. Cognitive radio has been pro-More complex instantiations that take into account additional posed for disaster scenarios. In [16], the authors proposepolicy constraints can also be specified and are an interesting a modification of the IEEE 802.11 MAC for cognitive ra-

subject for futureworir n

dios, while Rondeau et al. [19] describe their experiences insubject for future work.v

building and testing a cognitive engine for a point-to-pointwireless link. More recently, the SDR Forum has announced

V. RELATED WORK... a Smart Radio Challenge compeXtiton, where they proposeThe need for integrated and interoperable systems for co- the idea of using cognitive radios for sharing information

ordination and information sharing between first responders between first responders [3]. The SAFIRE architecture not

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only complements such efforts but also extends them by ACKNOWLEDGMENTSadvocating a generalized multi-layered multi-objective policy This research was supported thanks to grants from the Nat-based framework for tuning a cognitive radio's parameters. ural Sciences and Engineering Research Council of Canada,

Delay tolerant networks have only recently been studied the Canada Research Chair Program, Nortel Networks, Intel[10]. Their applications include Internet connectivity for rural Corporation, and Sprint Corporation. We would also like toareas [20], information collection in disaster scenarios [24], thank our colleague, Saba Gul, and our anonymous reviewersand even interplanetary communication [7]. In these applica- for their valuable feedback and suggestions.tions, lower layers of the protocol stack are unaware of thedelay-tolerant nature of the network. In our work, we employthe use of policies at the radio layer, that take into account REFERENCESrequirements at higher layers (such as DTN). This aspect of [1] Standards for Privacy of Individually Identifiable Health Information.radio configuration has not been previously addressed in the Office of the Secretary, Department of Health and Human Services,research literature. Federal Register, 67(157):53182-53273.

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