Bluetooth: carrying voice over ACL links

Abstract

The Bluetmth technology will enable m e n to c0Mect a wide range of electronic devices such as laplops, headsets, cellular phones etc. Bluetooth devices can connect to form a piconel, which consists of a master and upto 7 slaves. m e master controls the medium access in the piconet using a polling scheme. Two types of connections can be established in a piconet: the Synchronous Connection-Oriented (SCO) link, and the Asynchronous Counectiooless (ACL) link. SCO links provide a circuit-oriented service with constant bandwidth based on a fixed and periodic allocation of slots. They require a pair of slots once every two, four or six slots, depending upon the SCO packet used. ACL Connections, on the other hand, provide a packet-oriented service and span over 1, 3 or 5 slots. The master of the piconet uses: a polling mechanism to divide the piconet bandwldth among the ACL links. Since SCO links require a periodic Pllwtion of a pair of slots, they leave very little of the piconet bandwidth available to ACL links. Moreover, the controlled access of Bluetooth ensum that no ACL link gets starved. Under such an aeegs mechanism, ACL links may be s a c i e n t to carry high-quality voice and SCO links may not he n e e d d Our simulation and hardware experiments show that though the voice quality is affected slightly by using ACL instead of SCO links for voice, TCP connections perform much better if SCO links are not used. This paper. thus, makes a case for using ACL in place of SCO links for carrying voice. This renders SCO links redundant.

The ubiQoS middleware for audio streaming to bluetooth devices

“…In addition, our experiments have pointed out that the performance of ACL links significantly suffers from the concurrent usage of SCO. This result has also emerged in [4] As a conclusive remark, the collected data point out that the performance of our Java-based middleware, in terms of both throughput and packet delay, is close to the Bluetooth raw hardware performance [4]. This confirms the viability of flexible application-level overlays to support QoS-enabled audio streaming, even when exploiting the Bluetooth links as the last-meter connectivity technology in the wireless Internet.…”

“…However, even in the best case of SCO links using HV1 packets and requiring only 2 time slots every 6, the SCO exploitation leaves very little of the piconet bandwidth available to other links. In practice, no more than two SCO links can be concurrently active in the same piconet and, also in this case, the other connections may easily get starved [4].…”

“…Synchronous Connection Oriented (SCO) links, instead, are circuitoriented connections, designed to support time-bounded transmissions such as voice streaming. The usage of SCO links may leave very little of the piconet bandwidth available to ACL links [4]. Depending on service and user requirements, streaming services to Bluetooth devices should be capable of choosing the most suitable link type.…”

Analysis of a polling system for telephony traffic with application to wireless LANs

“…Li and M. data applications and assumed that customers arrive at queues according to a Poisson process. Increasingly, interest in polling systems is shifting from computer data applications to multimedia applications, e.g., in IEEE 802.11 wireless LANs [8], Bluetooth [9], and DOC-SIS systems [10]. Particularly in 802.11 MAC, the Point Coordination Function (PCF) mode of operation, which is a polling-based mechanism, alternates with the Distributed Coordination Function (DCF) mode of operation, a contentionbased channel access mechanism.…”

Middleware-level QoS differentiation in the wireless Internet: the ubiQoS solution for audio streaming over Bluetooth

“…In fact, most commercial Bluetooth chips transfer application data over SCO as audio pulse code modulation samples, by exploiting lossy codecs based on continuously variable slope delta modulation before transmitting the data over the air. In addition, the SCO isochronicity requirements hardly match with software scheduling and the SCO support in most Bluetooth stacks for Linux and Microsoft Windows is demonstrating to be still immature, thus leading to very poor performance [17].…”