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A Bluetooth Network Dynamic Graph AICT2014 : The Tenth Advanced International Conference on Telecommunications A Bluetooth Network Dynamic Graph Celio Marcio Soares Ferreira, Alejandro C. Frery Saul Delabrida, Ricardo Augusto R. Oliveira, Instituto de Computac¸ao˜ Mateus Freire Carneiro Haroldo Santos Gambini Universidade Federal de Alagoas (UFAL) Computer Science Department Computer Science Department Maceio,´ AL, Brasil Federal University of Ouro Preto (UFOP) Federal University of Ouro Preto (UFOP) e-mail: [email protected] Ouro Preto, Minas Gerais, Brasil Ouro Preto, Minas Gerais, Brasil e-mail: [email protected], e-mail: [email protected], [email protected] frrabelo, [email protected] Abstract—Bluetooth uses a communication technique called The collateral effects of frequency-hopping in Bluetooth, frequency-hopping which has some collateral effects. One of these such as the delay in discovery phase, show the relevance of is a significant delay time during the phase of discovery of nodes. a Bluetooth network graph model. It is important to devise a To precisely estimate this delay, we use real and simulated devices, realistic model, having procedures and constraints consistent and we measure the elapsed time until a Piconet formation. Our with the technology specification. contribution is modeling the Bluetooth network as a dynamic graph, adding the frequency-hopping procedures, Piconet limits In this work, we have the following contributions: and network constraints. These new components render a model which is more consistent with the Bluetooth network technology A Bluetooth network dynamic graph, with: specification than those presented so far. Our graph can be used as a basis for realistic optimization models. • The Piconet and Scatternet characterization and topol- ogy constraints; Keywords—bluetooth; scatternet; frequency hopping; dynamic graph. • Master and slaves node rules; • The proposal, implementation and validation of two procedures: FHS() and Disc(), which represent a I. INTRODUCTION device frequency hopping sequence synchronization and discovery of devices. In 2012, 1:1 billion mobile phones were shipped, almost 100 percent with Bluetooth technology [1]; but, despite this These new procedures and network constraints characterize popularity, Bluetooth network applications are not yet explored our Bluetooth network graph as a dynamic graph. in their full potential. The new-coming wearable devices, like smart-watches, and smart-glasses to name a few, use Bluetooth In Section II, we describe the initial formation process of a intensively. New popular apps, like firechat, also depend on Piconet. Section III discusses the related work. In Section IV the ad hoc Bluetooth network formation. The possibility of the initial connection delay time is identified by simulation forming wider-ranging ad hoc networks enhances their most and real experiments. In Section V, we present the dynamic common use: files exchange apps and mono headsets. Bluetooth network graph model. Finally, the conclusions are in Section VI. During communication, Bluetooth devices do not use a fixed frequency; they use frequency-hopping. Therefore, for II. PICONET - THE BASIC BLUETOOTH NETWORK a link formation, a device discovery phase is firstly needed. FORMATION In the device discovery phase, one device scans for another In a Piconet, a device assumes the role of master or slave, device, and both send and listen messages, respectively, in a and two distinct phases are required to connect: the discovery pseudo-random frequency sequence, until a frequency coinci- and the link formation. dence occurs and the synchronization messages are delivered. During the discovery phase, the candidate for the master Even in a smallest network with two nodes, there is a delay device goes into the INQUIRY state, looking for the devices time as consequence of the randomness, this prohibits Blue- candidates for the slave in an INQUIRY SCAN state. tooth for latency-sensitive applications. During the INQUIRY state, the searching device sends an The frequency-hopping sequence and all data flows are IDentifier (ID) by broadcast using 32 of the 79 frequencies de- coordinated centrally by a node called master, in a master- fined by Bluetooth specification. The sequence of frequencies slave point-to-multipoint network called Piconet. Each Piconet that will be used to broadcast ID messages, is a pseudo-random contains only one master, and can have a maximum of seven calculate, derived from the clock of the device. The set of this active slave nodes communicating to 10 m range. frequencies is called Inquiry Hopping Sequence (IHS). To expand the limits of this communication, we prefer The candidate for slave device in INQUIRY SCAN state Scatternets. They are collections of Piconets joined by a Bridge listens to broadcasts ID, on the same 32 IHS frequencies, node and coordinated by a protocol. hopping in a pseudo-random sequence derived from its clock. Copyright (c) IARIA, 2014. ISBN: 978-1-61208-360-5 76 AICT2014 : The Tenth Advanced International Conference on Telecommunications In this phase, candidates for master and slaves send and of graphs can be modeled as a Markov chain Clementi, Monti, listen messages respectively in a sequence of pseudo-random Pasquale e Silvestri [10], whose transitions describe by the frequency hops, until a frequency coincidence occurs. A time model of moving nodes. slot difference collaborates with the increased likelihood of the device hearing the same channel on which a ID was listened: Ferraguto, Mambrini, Panconesi and Petrioli [11] proposes the devices in INQUIRY state hop in time slots of 312:5µs a Bluetooth network graph model, where the links can be n faster than the standard Bluetooth 625µs used by devices in described by devices randomly distributed in the unit square, c(n) r(n) INQUIRY SCAN. the function is the neighborhood of each device and is the range of each device. With this, the Bluetooth network After receiving an ID, the candidate for slave device is denoted by the graph BT (r(n); c(n)). assumes a state called INQUIRY RESPONSE, and responds Jedda, Jourdan and Zaguia [2] show, by ns-2 simulation, to the request by sending its network address and clock, in a that the parameters changes related to Bluetooth discovery packet called frequency-hopping synchronization (FHS), using phase, are more significant in static Scatternet protocols, that the same frequencies of IHS. Then, the device waits for the use use the ALTERNATE strategy, than in dynamic Scatternet backoff a random value of time slots (0 − 639:375)µs, with protocols as in Law, Mehta and Siu [6]. This opens a discussion the objective of minimizing collisions of responses, and goes about the importance of new propositions that include changes to PAGE SCAN state. in parameters related to the Bluetooth frequency-hopping. When the candidate for master device receives the FHS, The Random Geometric Graph (RGG) has been employed it enters a state of PAGE, and uses the information received for the characterization of Bluetooth network topology. Pet- from the FHS for synchronization and connection with the tarin, Pietracaprina and Pucci [9] discuss the expansion and candidates for slave device that have already been discovered diameter of RGG subgraphs induced by device discovery and are in the PAGE SCAN state. phase. Experimental evidence shows that BT (r(n); c(n)) is a During the PAGE state, the candidate for master device ideal model for the Bluetooth topology; see Ferraguto, Mam- selects a candidate for slave device to be connected sending brini, Panconesi and Petrioli [11]. Unlike our proposed model, packages to the candidate for slave devices previously discov- classical graph models of Bluetooth as Gupta and Kumar [12], ered using the sequence of estimated hops. Ferraguto, Mambrini, Panconesi and Petrioli [11], Crescenzi, Nocentini and Pietracaprina [13] and Pettarin, Pietracaprina After the PAGE process is complete, the Piconet is formed and Pucci [9], do not explore (i) the topology of a Piconet, and the devices gain a connected status and assume their (ii) the Scatternet formation, or (iii) the intrinsic influences of master and slaves roles. frequency-hopping communication. A correct mapping of frequency-hopping peculiarities is III. RELATED WORK essential for the suitable design of Bluetooth solutions and Jedda, Jourdan and Zaguia [2] analysed the impacts of applications. changing Bluetooth parameters on the static and dynamic Scatternet formation protocols. These parameters are related to IV. IDENTIFYING THE DELAY the use of the frequency hop communication technique. The In order to measure the elapsed time of a Piconet con- Scatternet formation on static protocols happens as follows; nection and verify the existence of a connection delay, we each node alternates randomly between the INQUIRY and generated Piconet instances, using simulation and real devices. INQUIRY SCAN Bluetooth discovery states, when one device discovers each other, a temporally Piconet is formed until being We used the UCBT [14], a ns-2 [8] extension that sim- destroyed at the end of the communication. They called this ulates Bluetooth, developed by the University of Cincinnati. mechanism of ALTERNATE, being examples of it: BlueStars Additionally, to verify the real scenario, we used the Lego Petrioli, Basagni and Chlamtac [3]; BlueMIS Zaguia, Stoj- NXT Mindstorm [15], and robots were assembled to establish menovic and Daadaa [4] and BlueNet Wang, Thomas and connections with each other via Bluetooth. The Bluetooth
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