Survey of Quality of Service in Bluetooth - Assignment Example

A Survey of Quality of Service ( QoS) in Bluetooth Bluetooth is a wireless connecting system. For a seamless connectivity it needs to adhere to Quality of Service on certain parameters as follows. ACL Link ACL (Asynchronous Connectionless link) is an asynchronous (packet-switched) connection between two devices This type of link is used primarily to transmit ACL packet data. The other data link type is SCO link( Synchronous correction orientation). The SCO link has some deficiencies to support the real-time applications. Some applications are delay sensitive like streaming voice and video. They require a variable and asymmetric bandwidth. But the SCO link can only provide a fixed symmetric bandwidth. As a result whenever there is any interference the quality of voice and video quality detoriates. The quality is also affected when multiple bit errors in audio/video frames are fed into a decoder. The ACL can handle the interferences more effectively even when there are bursts of bit errors .This can be proven by looking at the delay in re-transmissions on the ACL link. This is as small as 1.25 mseconds. So it is very clear that compared to the SCO link, the ACL link can manage the quality in the presence of interference in much better way. Certain applications require variable and asymmetric bandwidth. It can be supported by ACL link. For getting a realtime quality ACL link is more effective than SCO link. Resource control Normally two devices linked by bluetooth have one ACL link. As a result there are different applications on a device that need to use the same ACL link . There could be one single BB link to a host running multiple L2cap channels or a host with BB links to multiple devices. In either case the Qos parameters are not specified and are manufacturer specific. They may have different applications running on them and all of them have compete for resources over the ACL link. Quality of Service (QoS) requirements for bandwidth and delay for these traffic flows need not be the same. Furthermore devices When there are more than one devices in a Piconet, the available air-interface bandwidth has to be shared by them. Therefore devices need to compete for resources in a Piconet. An equal division or sharing of the resources among all these devices may not be guaranteed when there is a multiple traffic flow. Neither we can satisfy the needs of the Quality of Service. Unless resource allocation is controlled it is difficult to guarantee that the QoS requirements of each flow is satisfied. Service differentiation In case of a multiple flow of traffic Service differentiation is needed. It chooses to provide better service to one traffic flow. Which in other words means providing not so god service to certain traffic flow. There are QoS parameters for different features like bandwidth and delay. The service level needs to be specified as per those parameters. Sometimes it may happen that a higher bandwidth provides lower delay. Because of the service differentiation the capacity of the system may not improve. All it can do is to use limited amount of resources as per the needs of the different traffic flows. There could be two QoS parameters : (i) an application constraint denoting the importance degree of a message (ii) an end-to-end delivery deadline (LNCS). There could be two scheduling accounting process- One-Round Robin (1-RR) which is a local scheduling accounting for the two QoS parameters. Another one is Class-Based Earliest Deadline First (CB-EDF)which is a new Bluetooth global scheduling. In this way the two QoS parameters can be compared at the global level. CB-EDF has shown a better service differentiation than enhanced 1-RR because with the presence of the constrains of muliple applications , it allows the messages to coexist. Bluetooth configuration The role of Quality of Service becomes very important in case of contention for resources between traffic flows That definitely does not undermine the need for QoS compliance for the configuration of the Bluetooth link in case of a single flow .For example - Flush Timeout setting, Multi-slot control and Maximum poll interval, could be some of the issues. If the number of retransmissions needs to be reduced the FEC (forward error correction) schemes is needed. If the ARQ scheme (automatic retransmission request) is used the data will be retransmitted and an acknowledgement is received. This confirms a successful transmission. If a pre-defined time-out occursthen it may not be confirmed. Each packet has a CRC (cyclic redundancy check) code. This helps the receiver to check an error free transmission. Whether some functions in the Bluetooth layer should be left to the Bluetooth layer is a debatable point. For example the information regarding whether FEC will be used or multi-slot packets will be used, is there in the Bluetooth layer. Depending on the wireless link conditions it can choose the best packet type for transmission Bluetooth bitpipe Since the main purpose of the Bluetooth technology is to provide a low cost wireless interface, it has to be a simple mechanism. Elaborate and complex QoS mechanisms are self defeating factors for the Bluetooth. The Bluetooth datalink layer can be taken as a simple bitpipe. Other QoS problem can be solved at the higher layers. It should be noted that the delay is even higher- when smaller packets are used when FEC is applied when the bandwidth has to be shared with other devices and when there are re-transmissions on the air-interface. The Host Controller (HC) buffering delay is a difficult point.If the HC buffer size is reduced, this can be taken care of. But the HC buffer can be reduced to a limited extent only. The content of the HC buffer decides which tasks will be scheduled by the Link Manager.. For an efficient scheduling of tasks by the link manager the Host Controller buffer needs a minimum size. So we need to look for other solutions that do not involve the HC buffer size, but different traffic treatment in the HC buffer remains as it is. Wireless link characteristics Just like other wireless interfaces, Bluetooth has the similar characteristics. These are basically in terms of bandwidth and delay compared to fixed link interfaces. The Bluetooth link has limited bandwidth. The delay and delay variation in Bluetooth link is comparatively high than the fixed line interfaces. There are no specific features in the blue tooth to support efficient handovers. It also has a relatively long link setup delay. It is assumed that the bluetooth will be functioning in presence of interferences but the effective bandwidth and delay characteristics of the bluetooth do get affected by the interferences. In the higher layers normally the bluetooth link tries to hide the wireless link characteristics but sometimes it fails to do so. So the characteristics of the wireless link have to be considered in the higher layers. For instance in the application of header layers compression on the wireless link (ROHC) the wireless link characteristics have been taken into account in the higher layers. QoS in Piconet and Scatternet The Bluetooth devices can interact with one or more other Bluetooth devices in variuos different manners. When only two devices are involved it is called a piconet which is an ad-hoc network. Proximity of piconets creates overlapping coverage areas. This is known as a Scatternet. The maximum number could be upto eight devices. The multiple piconets (PMP nodes) act as gateways among piconets. The nodes that act as slaves in one piconet can be a master or slave in another piconet. The time division multiplexing makes it possible. The piconets have their own frequency hopping channel. By time division multiplexing it becomes possible for the devices in multiple piconets to participate at the appropriate time. A distributed scatternet formation algorithms should be developed, for masters and PMP nodes in a scatternet so that bandwidth reservation and delay constraint can be satisfied. QoS guarantees Quantitative Guarantee- these are guarantees in specific numbers These specific guarantees or hard guarantees are the best for QoS. But it is difficult to provide such guarantees because of other variable factors also but when the variable factors are not adverse these specifics are almost similar to fixed line situations. Statistical guarantee – this type of guarantee is based on probability calculus. There is some relaxation compared to the specific number like the above. Qualitative guarantee- This qualifies a given parameter. There is more flexibility than the quantitative guarantee and some uncertain terms are also used . Relative Guarantee- This is the weakest form of guarantee because it is related to other guarantees in the system. It helps only when all other factors are in ideal situation. QoS parameters Bandwidth – The bandwidth may or may not be a constant. Some applications have specifications of the bandwidth but in many cases it may depend on a traffic specification or it can be delay bound. So it may be a constant or a variable. Delay and delay variation- In case of real time and streaming audio or vides applications there may be strict specification. Reliability- Although FEC can correct some errors, it can not be a reliable channel. Another reliability factor is to re-transmission is applying ARQ In some applications reliability is more important than delay whereas in other applications delay has priority over reliability. References:- LNCS( lecture notes in computer science)on www.springer.com. Retrieved 23 April 2007 Bluetooth.com. Home Page. Retrieved 23 April 2007http://www.bluetooth.com/> White papers on Whitepapers.techrepublic.com.Retrieved 23 April 2007 http://www.whitepapers.techrepublic.com/ Actapress.com (393) communication systems and networks 2003.on actapress.com. retrieved 23 April, 2007. http://www.actapress.com/ Grouper.iee.org Home page. retrieved 23 April, 2007 http://grouper.iee.org/ Ieice transactions on communications 2005 Home page retrieved 23 April, 2007http://www.ieice.com/ www.objs.com Home page retrieved 23 April, 2007 http://www.objs.com/ ieeexplore.ieee.org Homepage retrieved 23 April, 2007 http://www.ieeexplore.ieee.com/ www.techinterviews.com home page retrieved 23 April, 2007 . 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