BlueCube: Constructing a Hypercube Parallel Computing and Communication Environment over Bluetooth Radio System* Chao-Tsun Chang+, Chih-Yung Chang++, Jang-Ping Sheu+ + Department of Computer Science and Information Engineering, National Central University, Chung-Li, Taiwan
[email protected],
[email protected] ++ Department of Computer Science and Information Engineering, Tamkang University, Taipei, Taiwan
[email protected] Abstract In existing parallel computing structures, hypercubes have several distinct advantages; they support parallel computing, provide disjoint path and tolerate faults. If devices with computing capabilities can be linked as a Hypercube by taking advantage of Bluetooth radio’s features, then a high performance computing and efficient communication environment can be established by applying currently used algorithms. This work is a pilot study of applying Bluetooth wireless technology to construct a parallel computation and communication environment. A three-stage distributed construction protocol is presented for automatically constructing a hypercube computing environment from Bluetooth devices. The proposed protocol tackles the link construction, role assignment, scatternet formation and network management problems, to construct efficiently a hypercube structure. The proposed protocol enables Bluetooth devices easily to construct a routing path, tolerate faults and create disjoint paths. Parallel and distributed computing will be realized in a Bluetooth wireless environment. Experimental results show the proposed protocol will be able to set up a scatternet that is appropriate for parallel computing and communications.*
1. Introduction The simultaneous use of the computing power of many machines, to share large numbers of computations has been extensively studied in recent years. Studies of grid computing [1], and computation and communication in heterogeneous networks of workstations (NOW) [2] had addressed wired networks. Bluetooth [3] is a new wireless technology that has been gradually installed in various machines with computing power, including desktop PCs, notebooks, Tablet PCs, workstations, and so on. Wireless connection technology dynamically links up various *
This work was supported by the National Science Council of the Republic of China under grant NSC 91-2219-032-006 and NSC 91-2213-E-032-036.
Proceedings of the 2003 International Conference on Parallel Processing (ICPP’03) 0190-3918/03 $ 17.00 © 2003 IEEE
machines more flexibly and easily than before, and provides communication channels among machines of various types. The system uses the computing power of machines of different types to share computational workloads and thereby increase the power of mobile computing. Bluetooth radio operates in the 2.4GHz unlicensed ISM band. It searches and connects with other Bluetooth devices using the inquiry/inquiry scan and the page/page scan operations. Then, A scatternet is a wireless network of several piconets; bridge devices which serve more than one piconet [4], are responsible for cross-piconet communication and service [5][6][7]. A bridge can exist as a slave in two piconets simultaneously; it can also function as a master and slave, providing services in two piconets. When two devices that are not in a single piconet want to communicate, a routing path must be established [8][10]. Without competent role assignment and pairing of connections, the constructed scatternet may be disconnected, causing data not to be deliverable among devices. Previous research [9] has used Bernoulli trials to determine the role of each device and thus overcome this problem. This approach not only fulfils the basic requirements of a connection between piconets, but it also minimizes the number of piconets in the scatternet. However, the structure of the linked scatternet has not been explored and a scatternet cannot perform communication and computation effectively. Also, too much time is spent on collecting information from the various piconets, to decide whether the requirements for being connected have been met, and thus determine whether the number of piconets should be increased or reduced. Previous work [10] has proposed the Routing Vector Method (RVM) to construct a routing path between two devices in a connected scatternet. The method applies the flooding scheme to search for a destination. However, an improper scatternet structure will lengthen the route path of the two communicating devices, increasing delay time and the consumption of bandwidth and electrical energy. This study proposes a three-stage distributed protocol for constructing a hypercube environment by applying encoding techniques and role switch operations in
Bluetooth scatternet. The proposed protocol tackles the link construction, role assignment, scatternet formation and network management problems, to construct efficiently a hypercube structure. The proposed protocol enables Bluetooth devices easily to construct a routing path, tolerate faults and create disjoint paths. The rest of this work is organized as follows. Section II introduces the background of Bluetooth and the basic concepts of BlueCube construction. Section III presents the three-stage protocol for constructing a BlueCube, enabling Bluetooth device to build an appropriate parallel computing and communication environment. Section IV considers the performance of the proposed protocol. Section V draws the conclusions of this study.
2. Background and Basic Concepts In a Bluetooth wireless network, the formation of a piconet involves the inquiry/inquiry scan and the page/page scan procedures [7][9]. Doing so takes a large proportion of the connection time and power. If the Bluetooth devices are arbitrarily connected to other devices without proper assignment of roles, a critical point of scatternet may exist, at which the network is disconnected when a link is broken due to power exhaustion, fault or interference [13]. Accordingly, adequate role assignment and management in the inquiry and inquiry scan state will prevent disconnection and inefficiency. The proposed protocol provides distributed connection among Bluetooth devices, without any coordinator to collect information from all devices. The connection process works in the following three phases. Phase I. Ring Construction Phase(RCP) A coding mechanism is adopted to construct a ring scatternet to maximize the dimensions of a hypercube. All devices inside a ring scatternet form a hypercube in the following phases. Phase II. Scatternet Construction Phase(SCP) The SCP phase has two purposes. One is to reduce the number of piconets and devices with the bridge role and the other is to connect those devices that have not yet participated in the ring scatternet with the master devices in the ring. Some devices will apply the piconet combination, piconet splitting and role switch operations so that number of piconets and bridge devices is reduced. Phase III. BlueCube Construction Phase(BCP) This phase uses the scatternet generated in the previous two phases, without increasing the number of piconets, to enable all devices in the ring to establish a hypercube according to a distributed algorithm. The constructed BlueCube Computing Environment will support the easy building of a routing path, tolerate faults and provide disjoint paths.
3. Protocol for Constructing a BlueCube
Proceedings of the 2003 International Conference on Parallel Processing (ICPP’03) 0190-3918/03 $ 17.00 © 2003 IEEE
This section details a BlueCube protocol for constructing a parallel computing and communication environment. First, some terms are defined. Definition : Degree of Connection (DOC) DOC represents the degree (or dimensions) of a BlueCube established by a scatternet. When two scatternets are to be linked together, their DOC values are compared; they can link up only when their DOC values equal, with initial values of zero. Also, 2DOC is the number of devices in the scatternet. Definition : 01* Sequence A 01* sequence is a regular expression of bits. The sequence will be represented with a leading 0, followed by 0 or more repetition of 1. Examples of 01* sequences are 0, 01, 011, 0111, and so on. Definition :Connection Key (CK) CK value is NULL or a series of numerals 0 and 1, whose initial value is NULL. Every device must maintain a certain CK value, which identifies the device to determine whether it should perform inquiry or inquiry scan operation. Definition : Constructor Device in a scatternet whose CK value matches a 01* sequence is known as a constructor. Symbols Constructor(I)d and Constructor(IS)d represent device d in the inquiry and inquiry scan state, respectively. Note that, the proposed protocol will guarantee that, at any given time, only one constructor represents a scatternet in which it is located, and this constructor will connect to another scatternet’s constructor with the same DOC value. Some assumptions are made regarding the environment considered herein. (1) All Bluetooth devices are within a range that enables a connection to be established. Restated, any two devices can receive signals sent out by each other. (2) All Bluetooth devices know how many devices are present in the environment [9][15]. (3) In the initial stage, no link existed between any two Bluetooth devices. In the Phase I, every device will maintain information on CK and DOC. An n-degree BlueCube structure can be constructed by connecting two n-1 degree subCubes. To construct an n-degree BlueCube, one constructor will represent the connected n-1 degree subCube and connect to other constructor of connected n-1 degree subCube. Every device in a connected subCube will use its CK value to determine whether it is the constructor of this scatternet. The encoding of the CK value guarantees that exactly one constructor represents the currently connected scatternet. When two scatternets’ constructors are to be connected, they compare their DOC values. They can only form a larger scatternet if their DOC values are equal, implying that they have the same degree, and so can form a larger hypercube. Assume that the number of devices
required to construct a BlueCube is n. The three-phase BlueCube protocol is described below, with examples.
B I
§ CK NULL ¨ ¨ 0 © DOC
· ¸ ¸ ¹
§ CK NULL ¨ ¨ DOC 0 ©
· ¸ ¸ ¹
A I S
(a).Initial state
§ CK ¨ ¨ DOC ©
0 · ¸ 1 ¸¹
CK A §¨¨ DOC
1 · ¸ 1 ¸¹
B
©
(b).Piconet formed by twin devices
Figure 1: Initial connection of devices A and B.
3.1 The Ring Construction Phase (Phase I) Initially, the DOC value is zero. The Ring Construction Procedure includes the following steps and stops only when the number of devices in a ring scatternet exceeds half the number of all devices. C
C
B § CK ¨ ¨ DOC ©
0 · ¸ 1 ¸¹
§ CK ¨ ¨ DOC ©
0 · ¸ 1 ¸¹
§ CK ¨ ¨ DOC ©
1 · ¸ 1 ¸¹
§ CK ¨ ¨ DOC ©
1 · ¸ 1 ¸¹
D
A
(a)Ring scatternet formation at CK=0 and DOC=1.
D
B § CK ¨ ¨ DOC ©
00 · ¸ 2¸ ¹
§ CK ¨ ¨ DOC ©
01 · ¸ 2¸ ¹
§ CK ¨ ¨ DOC ©
A
§ CK ¨ ¨ DOC ©
10 · ¸ 2¸ ¹
11 · ¸ 2¸ ¹
(b)Connection of devices B and C and modification of CK and DOC values.
Figure 2: Connected linkage for the second time in the Phase I
Ring Construction Procedure (RCP) Step 1: Every device attempts to construct a ring scatternet. The value of DOC is used to evaluate the number of devices, say k=2DOC, in the connected scatternet. Step 2: If k
