A Survey of Quality of Service ( QoS) in BluetoothBluetooth 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 controlNormally 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 differentiationIn 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.