1.8 Managing With Bluetooth
Some parts of the Bluetooth system have to manage the links, establishing ACL links as needed and disconnecting when they are finished with them. L2CAP could fulfill this function, but since links must also be managed at the RFCOMM and SDP levels, it makes sense to have a separate device manager.
The core specification of Bluetooth does not say how the connections should be managed, although the security white paper gives some hints. The reason for this lack of mention in the specification is that device management does not affect end-to-end interoperation, so it is safe to leave it up to individual implementers to find their own solutions. Furthermore, the most appropriate solution is likely to be different for different devices. For instance, a headset only has to handle a single link, which is used for SDP and the headset service, so management is likely to be pretty simple, whereas a LAN access point has to juggle multiple links and balance bandwidth between them, so management of the links will be much more complex.
Bearing in mind that no single solution will be optimal for all possible devices, Figure 110 shows a possible protocol stack with a device and security manager that can handle establishment and configuration of the links.
Figure 110 Management of the Bluetooth protocol stack.
The device manager interfaces to the HCI layer, SDP, RFCOMM, L2CAP, and to applications. It can provide the following facilities:
Fault managementDetects, isolates, and corrects abnormal operation.
Accounting managementEnables charging for use of managed objects and services.
Configuration and name managementControls, identifies, collects data from, and provides data to managed objects to assist in interconnection services.
Performance managementEvaluates the behaviour of managed objects and the effectiveness of communication activities.
Security managementProvides security management to protect managed objects and services.
Those familiar with the OSI model will recognise these facilities as those provided by OSI management.
Applications will have to register with the Bluetooth device manager to use Bluetooth links. They may then ask the device manager for connections, and request particular security and quality of service levels. If all applications go through the device manager, this allows it to create a database of higher layer protocols, applications, and services using links.
The device manager can also handle timeouts, shutting down links when they are no longer needed.
Bluetooth's management facilities do not have to be handled by a separate device management entity as described above. This function could be built into L2CAP, or into a profile application. However it is done, there must be some part of every Bluetooth implementation which handles management of the links.