All answers have been held as short as possible and require an understanding and study of the corresponding chapter of the book.
Bluetooth transfer speeds depend on how many users exchange data in a Piconet, how much data is exchanged by the individual users at a certain time and what kind of multislot packets are used. In the ideal scenario with only two devices in which only one device has a lot of data to send, a peak data rate of 723 kbit/s can be achieved for one of the two devices.
FHSS (Frequency Hopping Spread Spectrum) sends each packet on a different channel (frequency). This avoids using the same channel for a prolonged amount of time which might already be in use by another network such as a Wireless LAN. FHSS also simplifies device configuration as no channel number has to be selected by the user in the Bluetooth settings. Bluetooth 1.2 introduces adaptive frequency hopping which avoids channels with high error rates caused by parallel transmissions from other networks. This reduces transmission errors and the influence on other networks in the same area while at the same time increasing the overall transmission speed.
The Inquiry procedure is invoked to search for unknown Bluetooth devices in the area. If a Bluetooth device is visible to other devices it responds to an inquiry packet it detects by sending its device ID. A paging on the other hand is used to directly establish contact with a Bluetooth device which is already known. If a Bluetooth device only wants to be accessible for devices with which it has previously communicated with, it only responds to paging messages and never to inquiries.
Bluetooth offers a number of power saving mechanisms and states: Connection hold: A device deactivates its transceiver for a certain time. Connection sniff: A device deactivates its transceiver for a certain time but checks at predefined times if the master device wants to resume communication. If not, the device automatically returns to the power save state. Connection park: The devices releases its device address and uses a very long timeout value before checking again if the master device would like to reestablish contact.
The link manager has the following tasks: Establishment of an ACL, SCO or eSCO connection, configuration of the connection, activation of the enhanced data rate mode, execution of a master-slave roll change procedure, pairing, authentication and ciphering management, adaptive frequency hopping management, and activation of different power save modes when appropriate.
The L2CAP layer’s protocol service multiplexer is used during connection establishment to select to which of several higher protocol layers to connect to. In addition, an individual connection ID is used on the L2CAP layer for each connection to identify packets. This allows two devices to establish several simultaneous connections between each other for different higher layer applications.
The service discovery database contains information about all services offered by a Bluetooth device. Other devices can query this database during connection establishment to detect which services are offered and how certain parameters have to be set in order to access them.
Each Bluetooth profile using the RFCOMM layer has to register with the Service Discovery database. If a remote device wants to use the service offered by the profile it has to query the database in order to retrieve the RFCOMM channel number which has been assigned to this profile. As the number is dynamically allocated the database has to be queried for every new connection.
Authentication: Two Bluetooth devices are able to authenticate each other if they have previously been paired.
Authorization: This is a security mechanism on the application level and allows to restrict access to applications to certain remote devices. This way it can be ensured that only some of the previously authenticated devices can access certain services. It might be desirable for example that only the notebook of a user can use the dial up connection profile of a phone. Other devices are barred from this profile but are allowed to transfer files from and to the mobile phone.
Bluetooth is a very versatile communication technology that can be used for a wide variety of different services. This ranges from services like exchange of electronic business cards and images to connecting headsets, mice and keyboards to PCs and tablets. The Bluetooth standard defines a number of profiles to ensure interoperability on the application level. A profile specifies how a service is supposed to work and in which way remote devices can communicate with it.
The object exchange (OBEX) profile has been designed for a fast and simple transmission of files and objects between two Bluetooth devices. The OBEX profile is the basis for the file transfer profile, the object push profile and the synchronization profile.
When using the hands-free profile, the hands-free set is only seen as a microphone and loudspeaker extension of the mobile phone. The connection to the network continues to be established by the mobile phone. The SIM access profile does just the opposite. With this profile, the mobile station is only used as a SIM card reader. All other functionalities including the GSM/UMTS transceiver are deactivated. The hands free set then uses the Bluetooth connection to access the SIM card and can perform all transactions between itself and the SIM card just as if the SIM card was directly inserted into the hands free-set. Such hands-free sets are more expensive than those just using the hands-free profile, as they have to contain a complete mobile phone unit including the GSM/UMTS module. This has the advantage, however, that an external antenna can be used. Furthermore, the mobile phone can be configured for the use of both the SIM access profile and the headset profile. While the mobile phone is used in the car, the hands-free set takes over. Once the user leaves the car and takes the mobile phone with him, incoming calls can automatically be redirected to the Bluetooth headset once again. This can not be done as easily with a hands free set in the car supporting the hands-free profile as the phone is unable to decide for incoming calls to which device to establish contact.
Answer 13 (2nd edition):
Removed, no longer relevant.
Answer 13 (3nd edition):
There are significant differences of classic Bluetooth and BLE on the air interface. While BT uses fast frequency hopping and 1 Mhz channels, BLE splits the 2.4 GHz ISM band into 40 channels of 2 MHz each and uses very slow frequency hopping. BLE only uses GFSK modulation and the datarate is not variable but fixed at 1 Mbit/s over a channel. This reduces the datarate to a few tens of kilobytes per second but in return significantly reduces power consumption.
The aim in BLE is not to establish a transparent channel between two devices but to transfer small amounts of data as power efficiently as possible. Therefore data is transmitted in a way that could be compared to reading and writing variables on a remote system.