Explain Bluetooth protocol stack with neat diagram

Mumbai University > Computer Engineering > Sem 6 > Mobile Communication and Computing

Marks: 10M

Year: May 2012, Dec.2012, 2013

1 Answer

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• AT: Attention sequence

• OBEX: Object Exchange

• TCS BIN: Telephony control protocol specification – binary

• BNEP: Bluetooth network encapsulation protocol

• SDP: Service discovery protocol

• RFCOMM: Radio frequency comm.

Radio Layer

• Radio layer defined the carrier frequencies and output power

• Bluetooth uses 2.4 GHZ license free band.

• Frequency hopping and TDD (time division duplex) is used for transmission with fast hopping rate of 1600 hops/s.

• It uses 79 hop carriers equally spaced with 1 MHz.

• Gaussian FSK used for modulation.

Baseband Layer

• Baseband layer performs frequency hopping to avoid interference and to access the medium.

• Defines physical links and many packet formats.

• It controls:

o Device Addressing

o Channel control through paging and inquiry methods

o Power saving operations

o Flow control and synchronization among Bluetooth devices.

Link Manager Protocol (LMP)

• The Link Manager protocol manages various aspects of the radio link between master and slave.

• The following functions are covered by LMP:

o Authentication, pairing and encryption

o Synchronization

o Capability negotiation

o QoS negotiation

o Power control

o Link Supervision

o State and transmission mode change

Logical Link Control and Adaptation Layer Protocol (L2CAP)

• L2CAP is layered over the Baseband Protocol and resides in the data link layer.

• L2CAP provides:

o Connection-oriented and connectionless data services to upper layer protocols with protocol multiplexing capability.

o Segmentation and reassembly operation.

o Group abstractions.

• L2CAP provides three different types of logical channels that are transported via ACL link between master and slave, these are:

o Connectionless used for broadcast

o Connection-oriented for data transfer with QoS flow specification.

o Signaling used to exchange signaling messages between L2CAP entities.

Host Controller Interface (HCI)

• The HCI provides a command interface to the baseband controller and link manager.

• It provides access to hardware status and control registers.

• Essentially this interface provides a uniform method of accessing the Bluetooth baseband capabilities.

• The HCI exists across 3 sections, The Host, Transport Layer, and Host Controller. Each of the sections has a different role to play in HCI system.

• HCI defines the set of functions of a Bluetooth module that are accessible to the host and its application.

• HCI can be seen as a software/hardware boundary.


• The RFCOMM protocol provides emulation of serial ports over the L2CAP protocol.

• It is a cable replacement protocol that provides a serial line interface to all the applications.

• The protocol is based on the ETSI standard TS 07.10.

• It supports multiple serial ports over a single physical channel.

Service Discovery Protocol (SDP)

• The service discovery protocol helps the applications to discover which services are available and to determine the characteristics of those available services.

• SDP defines only the discovery of services, not about their usage.

• New service is discovered as follows:

o Client sends a request to search for an interested service.

o Then the server responds to the client with the list of available services that match to the client’s criteria.

o The client uses the list to retrieve additional service attribute for the service of interest.


• Profiles are specifications which describe how Bluetooth should be used in a specific application and thus ensures that all devices from different manufacturers can seamlessly work with one another.

• There are about a dozen profiles:

Generic Access, Serial Port, Dial up Networking, FAX, Headset, LAN, Access Point, Generic Object Exchange (OBEX), File Transfer, Object Push, Synchronization, Cordless Telephony, and Intercom.

• The profile concept is used to decrease the risk of interoperability problems between different manufacturers’ products.

Telephony Control Protocol Specification Binary (TCS-BIN)

• To define call control signaling for the establishment of voice and data calls between Bluetooth devices TCS-BIN describes a binary, packet-based, bit-oriented protocol.

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