158 research outputs found
Clockwise: a mixed-media file system
This paper presents Clockwise, a mixed-media file system. The primary goal of Clockwise is to provide a storage architecture that supports the storage and retrieval of best-effort and real-time file system data. Clockwise provides an abstraction called a dynamic partition that groups lists of related (large) blocks on one or more disks. Dynamic partitions can grow and shrink in size and reading or writing of dynamic partitions can be scheduled explicitly. With respect to scheduling, Clockwise uses a novel strategy to pre-calculate schedule slack time and it schedules best-effort requests before queued real-time requests in this slack tim
Distributed On-Line Schedule Adaptation for Balanced Slot Allocation in Bluetooth Scatternets and other Wireless Ad-Hoc Network Architectures
In this paper we propose an algorithm for design and on the fly modification of the schedule of an ad-hoc wireless network in order to provide fair service guarantees under topological changes. The primary objective is to derive a distributed coordination method for schedule construction and modification in Bluetooth scatternets. The algorithm proposed here has wider applicability, to any wireless ad-hoc network that operates under a schedule where the transmissions at each slot are explicitly specified over a time period of length T. First we introduce a fluid model of the system where the conflict avoidance requirements of neighboring links are relaxed while the aspect of local channel sharing is captured. In that model we propose an algorithm where the nodes asynchronously re-adjust the rates allocated to their adjacent links based only on local information. We prove that from any initial condition the algorithm finds the max-min fair rate allocation in the fluid model. Hence if the iteration is performed constantly the rate allocation will track the optimal even in regimes of constant topology changes. Then we consider the slotted system and propose a modification method that applies directly on the slotted schedule, emulating the effect of the rate re-adjusment iteration of the fluid model. Through extensive experiments in networks with fixed and time varying topologies we show that the latter algorithm achieves balanced rate allocation in the actual slotted system that are very close to the max-min fair rates. The experiments show also that the algorithm is very robust on topology variations, with very good tracking properties of the max-min fair rate allocation
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Industrial multimedia over factory-floor networks
In this paper we describe a real-time industrial communication network able to support both controlrelated
and multimedia traffic. The industrial communication network is based on the PROFIBUS
standard, with multimedia capabilities being provided by an adequate integration of TCP/IP protocols into
the PROFIBUS stack. From the operational point of view the integration of TCP/IP into PROFIBUS is by
itself a challenge, since the master-slave nature of the PROFIBUS MAC makes complex the
implementation of the symmetry inherent to IP communications. From the timeliness point of view the
challenge is two folded. On one hand the multimedia traffic should not interfere with the timing
requirements of the "native" control-related PROFIBUS traffic (typically hard real-time). On the other
hand multimedia traffic requires certain levels of quality-of-service to be attained. In this paper we
provide a methodology that enables fulfilling the timing requirements for both types of traffic in these
real-time industrial LAN. Moreover, we describe suitable algorithms for the scheduling support of
concurrent multimedia streams
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