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.