Bluetooth Protocols

The Bluetooth protocols are the main reasons for Bluetooth communication. They can be mainly classified into four.
i) Core Protocols
ii) Cable Replacement Protocol
iii) Telephony Control Protocols
iv) Adopted Protocols

i) Core Protocols:

The Bluetooth Core protocols are embedded in every Bluetooth profile and provide transport and link management functions to all applications. They are again subdivided into:
a) Baseband Protocol
b) Link Manager Protocol (LMP)
c) Logical Link Control and Adoption Protocol (L2CAP)
d) Service Discovery Protocol (SDP)

a) Baseband Protocol:

The Baseband protocol enables the physical RF connection or, a link, between the two or more Bluetooth units that form a piconet. This protocol also synchronizes the transmission hopping frequencies and clocks of the individual Bluetooth devices in a piconet.

b) Link Manager Protocol (LMP):

The LMP is responsible for link setup and control between two or more Bluetooth devices. The LMP also controls the power modes and duty cycles of the Bluetooth radio, as well as the connection states of the Bluetooth device when attached to a piconet.

c) Logical Link Control and Adoption Protocol (L2CAP):

The Logical Link Control and Adoption Protocol (L2CAP) works in parallel with the LMP to transfer upper-level data to and from the Baseband layer. The big difference between L2CAP and LMP is that L2CAP provides services to the upper layer, which LMP does not.

d) Service Discovery Protocol (SDP):

The Service Discovery Protocol (SDP) provides for one device to query another about device information, services, and characteristics of those services. It also enables the establishment of a connection between those two devices.

ii) Cable Replacement Protocol:

The Bluetooth Specification includes just one protocol that addresses the wireless emulation of data typically sent over wire-based links—RFCOMM.

RFCOMM:

RFCOMM is a protocol that emulates an RS-232 serial connection between two devices. This is a cable-replacement protocol, which provides serial connection for upper-level services.

iii) Telephony Control Protocols:

The Telephony Control protocols enable Bluetooth devices to handle voice and data calls from Bluetooth-enabled devices. For a Bluetooth device to function as either a telephone or a modem, one of the two Telephony Control protocols must be implemented in a profile’s protocol stack. It contains two categories:

a) Telephony Control Specification—Binary
b) AT Commands

a) Telephony Control Specification—Binary:

Telephony Control Specification—Binary (TCS-BIN) defines the call control signaling necessary to establish voice and data calls between Bluetooth devices. It also defines the mobility management procedures used to handle groups of Bluetooth devices.

b) AT Commands

Bluetooth’s AT commands are used when a profile requires a Bluetooth device to be employed as either a phone or modem when connecting to a landline or cellular telephone system. It is used to control all the functions capable of being performed by a telephone or data modem

iv) Adopted Protocols:

In addition to the previous protocols, a number of protocols are established in other to work with the newer Bluetooth technology. This makes the Bluetooth devices to connect with global communications networks. Some adopted protocols are:
Point-to-Point Protocol (PPP), Transport Control Protocol/Internet Protocol/User Datagram, Protocol (TCP/IP/UDP), Object Exchange Protocol (OBEX), Infrared Mobile Communication (IrMC), Wireless Application Protocol (WAP), Wireless Application Environment (WAE), vCard, vCalendar, vMessage, and vNote (content formats) etc.

So, when, once a link is established between two Bluetooth devices, the Link Managers of each unit communicate with each other via the Link Manager Protocol. After getting links the communication starts.

Communication through Bluetooth

Piconet: When two or more Bluetooth devices are connected together (wirelessly), it forms a type of personal area network called Piconet. Each piconet can contain up to eight different Bluetooth devices.
Scatternet: Multiple piconets can be connected in larger scatternets. Linking from piconet to piconet enables Bluetooth devices to connect to larger local area networks, and to the global Internet.

Communication with and within piconets:

Within each piconet, one device serves as the master, while the other seven devices function as slaves. When all these seven devices communicate with a same frequency range of 2.4GHz at a time, the band will get so crowded that the various devices could start interfering with one another. To minimize interference issues, Bluetooth radios utilize a technique called spread spectrum frequency hopping.

Spread spectrum: Spread spectrum refers to a number of different techniques that divide the available radio band by frequency, time, or some other method.

Frequency Hopping: Frequency hopping is a common spread spectrum technique, where a signal hops from one frequency to another during the course of a single transmission. This technique also helps for secured communications.
In the Bluetooth module, the Bluetooth radio is constantly and randomly changing frequencies among a broad spectrum of frequencies, hopping to a new frequency after transmitting or receiving each packet of data. The Bluetooth transmission doesn’t stay on a single frequency for a long time to get impacted by interference with that frequency.

When two Bluetooth devices are connected together, they should hop at a same frequency, and in a correct sequence. The sequence is assigned by the internal clock setting in the Master unit. The slave units synchronize to the master unit’s clock, and so the datas get transferred without any interference.

Bluetooth radios can execute up to 1600 hops per second. The signal hops among 79 frequencies between 2.402GHz and 2.480GHz, at 1MHz intervals.

The Bluetooth signals are mainly data signals and voice signals.

For data transmission, Data signals utilize a technology called packet switching. With packet switching, data is divided into small groups, or packets, before it is transmitted. For voice transmission, Voice signals utilize a technology called circuit switching. With circuit switching, messages are not sliced into packets; instead, a dedicated channel (or circuit) is established for the duration of the transmission.

Speed of communication:

The communication in Bluetooth devices happens with a speed of 1Mbps (megabyte per second).

Advantages of Bluetooth technology

1. It is a wireless technology which helps to throw away wires and cables.

2. In wireless communicating technology like IR (Infra Red), the line of sight is a major problem; ie., during communication, the communicating devices should be kept in the same area or angle for data transfer. But, the Bluetooth technology eliminates this problem. In Bluetooth communication, the only requirement is - the devices should be kept within a 30 feet distance, and also, serves as omniditrectional..

3. Many wireless communications involves a one-to-one networking topology -- only one device talking at a time. But, the Bluetooth technology eliminates the one-to-one networking topology and paves the way for connecting any number of devices at a time.

4. Many wireless communicating technologies gets disconnected immediately after the data transmission gets over; we need to reconnect again for the next transmission. This makes the data transfer to act very slow. But, With Bluetooth, once we’re connected we’re always connected.

Applications of Bluetooth technology:

1. Mainly used for data transfer in mobile phones.

2. Used in head sets.

3. Data transfer in PC.

4. In cars connected with GPS.

5. In digital cameras.

6. For accessing LAN connections.

7. In MP3 players