Abstract:Protocol layers are a hierarchical model of
network or communication functions. The divisions of
the hierarchy ar...
band, ensuring communication compatibility
a. Data and voice access point :
The Bluetooth technology facilitate...
forming a piconet. This layer controls the Bluetooth
unit's synchronization and transmission frequency
hopping sequence. T...
• Multiplexing –
L2CAP must support protocol multiplexing
since a number of protocols (e.g. SDP,
RFCOMM and TCS Binary) ca...
OBEX Protocol
IrOBEX, shortly OBEX, is an optional
application layer protocol designed to enable units
supporting infrared...
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Protocols in Bluetooth


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Protocols in Bluetooth

  1. 1. Abstract:Protocol layers are a hierarchical model of network or communication functions. The divisions of the hierarchy are referred to as layers or levels, with each layer performing a specific task. In addition, each protocol layer obtains services from the protocol layer below it and performs services for the protocol layer above it. The Bluetooth system divides communication functions into protocol layers. The Bluetooth system consists of many existing protocols that are directly used or have been adapted to the specific use of the Bluetooth system. Protocols are often divided into groups that are used for different levels of communication (a protocol stack). Lower level protocols (such as protocols that are used to manage a radio link between specific points) are only used to create, manage, and disconnect transmission between specific points. Mid- level protocols (such as transmission control protocols) are used to create, manage, and disconnect a logical connection between endpoints that may have multiple link connections between them. High level protocols (application layer protocols) are used tolaunch, control, and close end-user applications. Some of the layers associated with the Bluetooth system include the baseband layer (physical layer), link layer, host controller interface (HCI), logical link control applications protocol (L2CAP), RF Communications protocol (RFCOMM), Object Exchange (OBEX), and service discovery. Keywords: Bluetooth, Bluetooth stack, protocols, layers, baseband, LMP, L2CAP, RFCOMM, Ad hoc networks, PANs. I.INTRODUCTION Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength radio waves in the ISM band from 2.4 to 2.485 GHz) from fixed and mobile devices, building personal area networks (PANs). Invented by telecom vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization. Bluetooth is managed by the Bluetooth Special Interest Group (SIG), which has more than 19,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. Bluetooth was standardized as IEEE 802.15.1, but the standard is no longer maintained. The SIG oversees the development of the specification, manages the qualification program, and protects the trademarks. To be marketed as a Bluetooth device, it must be qualified to standards defined by the SIG. A network of patents is required to implement the technology, which is licensed only for that qualifying device. Wireless data exchange standard Bluetooth uses a variety of protocols. Core protocols are defined by the trade organization Bluetooth SIG. Additional protocols have been adopted from other standards bodies. It an overview of the core protocols and those adopted protocols that are widely used. The Bluetooth protocol stack is split in two parts: a "controller stack" containing the timing critical radio interface, and a "host stack" dealing with high level data. The controller stack is generally implemented in a low cost silicon device containing the Bluetooth radio and a microprocessor. The host stack is generally implemented as part of an operating system, or as an installable package on top of an operating system. For integrated devices such as Bluetooth headsets, the host stack and controller stack can be run on the same microprocessor to reduce mass production costs; this is known as a hostless system. The Bluetooth technology answers the need for short range wireless connectivity within three areas: • Data and voice access points . • Cable replacement • Ad hoc networking The Bluetooth technology specification specifies a system solution comprising hardware, software and interoperability requirements. The Bluetooth radio operates in a globally available 2.4GHz ISM Protocols In Bluetooth
  2. 2. band, ensuring communication compatibility worldwide. a. Data and voice access point : The Bluetooth technology facilitates real time voice and data transmission. The technology makes it possible to connect any portable and stationary communication device as easily as switching on the light. You can, for instance, surf the Internet & send e-mail on your potable PC or notebook regardless of whether you are wirelessly connected through a mobile phone or through a wire bound connection (PSTN, ISDN,LSN,XDLS). Voice channel use the Continuous Variable Slope Delta Modulation (CVSD) coding scheme, and never retransmit voice packets. The CVSD was chosen for its robustness in handling dropped and damaged samples. Rising interference levels are experienced as increased background noise; even at bit error rate up to 4% the CVSD coded voice is quite audible. b. CABLE REPLACEMENT: The Bluetooth technology eliminates the use for numerous often proprietary cable attachments for connection of practically any kind of device. Connections are instant and they are maintained even when devices are not within line of sight. The range of each radio is approximately 10 meters but it can be extended around 100 meters with an optional amplifier. c. AD-HOC NETWORKING: A device equipped with Bluetooth radio establishes instant connection to another Bluetooth radio as soon as it comes into range. Since Bluetooth technology supports both point to point and point to multi point connection, several piconets can be established and linked together ad hoc. The Bluetooth technology is best described as multiple piconet structure. Piconet is a connection of devices connected via Bluetooth technology in an ad hoc fashion . A piconet starts with two connected devices ,such as portable PC and cellular phone and may grow into eight connected devices. All Bluetooth devices are peer units and have identical implementation. However, when establishing a piconet, one unit will act as a master and the other as a slave for the duration of piconet connection. Fig 1: Overview of Bluetooth. II. Architecture of Bluetooth Protocol. Fig 2: Architecture of Bluetooth Protocol. a. Radio The radio is used for specification of the air interfaces, i.e. frequencies, modulation, and transmit power.Bluetooth radio is a transceiver which transmits and receives modulated electrical signals from peer Bluetooth devices b. Baseband The Baseband and Link Control layer enables the physical RF link between Bluetooth units
  3. 3. forming a piconet. This layer controls the Bluetooth unit's synchronization and transmission frequency hopping sequence. The two different link types defined in Bluetooth, Synchronous Connection Oriented, SCO, and Asynchronous Connectionless, ACL, described in the section Link types, are also managed by this layer. The ACL links, for data, and the SCO links, mainly for audio, can be multiplexed to use the same RF link. The link defines “what” of packets can be used on a particular link. Also they fall under MAC layer. The Bluetooth baseband technology supports two link types: • Synchronous connection oriented (SCO) type (used primarily for voice) • Asynchronous connectionless (ACL) type (used primarily for packet data) Different master slave pairs of the same piconet structure can use different link types and the link type may change arbitrarily during a session. Each link “supports up to 16 different packet types. Four of these are control packets and are common for both SCO and ACL links. Both link types use a Time Division Duplex (TDD) scheme for full duplex transmission. SYNCHRONOUS CONNECTIONS ORIENTED TYPE: The SCO link is symmetric and typically supports time bound voice traffic. SCO packets are transmitted over reserved intervals. Once the connection is established, both master and slave units may send SCO packets without being polled. One SCO packet type allows both voice and data transmission ; with only the data portion being retransmitted when corrupted. ASYNCHRONOUS CONNECTIONLESS LINK TYPE: The ACL link is packet oriented and supports both, symmetric and asymmetric traffic. The master unit controls the link bandwidth and decides how much piconet bandwidth is given to each slave, and the symmetry of the traffic. Slaves must be polled before they can transmit data. The ACL link also supports broadcast messages from the master to all slaves in the piconet. In order to make different hardware implementations compatible, Bluetooth devices use the HCI as a common interface between the Bluetooth host (e.g. a portable PC) and the Bluetooth core. Higher-level protocols like the SDP, RFCOMM (emulating a serial port connection) and the TCP are interfaced to baseband services via the LLCAP. Among the issues LLCAP takes care of, is segmentation and reassemble to allow larger data packets to be carried over a Bluetooth baseband connection. The service discovery protocol allows applications to find out about available services and their characteristics when e.g. devices are moved or switched off. c. Audio Audio transmissions can be performed between one or more Bluetooth units, using many different usage models. Audio data do not go through the L2CAP layer (described below) but go directly, after opening a Bluetooth link and a straightforward set-up, between two Bluetooth units. d. Host Controller Interface, HCI The Host Controller Interface, HCI, provides a uniform interface method for accessing the Bluetooth hardware capabilities. It contains a command interface to the Baseband controller and link manager and access to hardware status. Finally, it contains control and event registers. e. Link Manager Protocol, LMP The Link Manager Protocol, LMP, is responsible for link set-up between Bluetooth units. It handles the control and negotiation of packet sizes used when transmitting data. The Link Manager Protocol also handles management of power modes, power consumption, and state of a Bluetooth unit in a piconet. Finally, this layer handles generation, exchange and control of link and encryption keys for authentication and encryption. f. Logical Link Control and Adaptation Protocol, L2CAP The Bluetooth logical link control and adaptation protocol, L2CAP, is situated over the Baseband layer and beside the Link Manager Protocol in the Bluetooth protocol stack. The L2CAP layer provides connection-oriented and connectionless data services to upper layers. The four main tasks for L2CAP are:
  4. 4. • Multiplexing – L2CAP must support protocol multiplexing since a number of protocols (e.g. SDP, RFCOMM and TCS Binary) can operate over L2CAP. • Segmentation and Reassembly – Data packets exceeding the MaximumTransmission Unit, MTU, must be segmented before being transmitted. This and the reverse functionality, reassemble, is performed by L2CAP. • Quality of Service – The establishment of an L2CAP connection allows the exchange of information regarding current Quality of Service for them connection between the two Bluetooth units. • Groups – The L2CAP specification supports a group abstraction that permits implementations for mapping groups on to a piconet. • An L2CAPimplementation must be uncomplicated and implying low overhead since it must be compatible with the limited computational resources in a small Bluetooth unit. g. Service Discovery Protocol, SDP The Service Discovery Protocol, SDP, defines how a Bluetooth client's application shall act to discover available Bluetooth servers' services and their. Bluetooth characteristics. The protocol defines how a client can search for a service based on specific attributes without the client knowing anything of the available services. The SDP provides means for the discovery of new services becoming available when the client enters an area where a Bluetooth server is operating. The SDP also provides functionality for detecting when a service is no longer available. • Cable replacement protocol h. Radio Frequency Communication , RFCOMM The Radio Frequency Communication RFCOMM protocol is a serial port emulation protocol. The protocol covers applications that make use of the serial ports of the unit. RFCOMM emulates RS-232 control and data signals over the Bluetooth baseband. It provides transport capabilities for upper level services, e.g. OBEX that use a serial line as the transport mechanism. i. Telephony control protocol Telephony Control – Binary The Telephony Control protocol – Binary, TCS Binary or TCS BIN, is a bit-oriented protocol, which defines the call control signalling for the establishment of speech and data calls between Bluetooth units. The protocol defines the signalling for establishment and release of calls between Bluetooth units. As well as signalling to ease the handling of groups of Bluetooth units. Furthermore, TCS Binary provides functionality to exchange signalling information unrelated to ongoing calls. Establishment of a voice or data call in a point-to- point configuration as well as in a point-to- multipoint configuration is covered in this protocol (note, after establishment, the transmission is from point to point). The TCS Binary is based on the ITU-T Recommendation. Telephony Control – AT Commands A number of AT-commands are supported for transmitting control signals for telephony control. These use the serial port emulation, RFCOMM, for transmission. j. Adopted protocols This section describes a number of protocols that are defined to be adopted to the Bluetooth protocol stack. Note some of these adaptations are at the moment incomplete. PPP The IETF Point-to-Point Protocol (PPP) in the Bluetooth technology is designed to run over RFCOMM to accomplish point-to-point connections. PPP is a packet-oriented protocol and must therefore use its serial mechanisms to convert the packet data stream into a serial data streams. TCP/UDP/IP The TCP/UDP/IP standards are defined to operate in Bluetooth units allowing them to communicate with other units connected, for instance, to the Internet. Hence, the Bluetooth unit can act as a bridge to the Internet. The TCP/IP/PPP protocol configuration is used for all Internet Bridge usage scenarios in Bluetooth 1.0 and for OBEX in future versions. The UDP/IP/PPP configuration is available as transport for WAP.
  5. 5. OBEX Protocol IrOBEX, shortly OBEX, is an optional application layer protocol designed to enable units supporting infrared communication to exchange a wide variety of data and commands in a resource- sensitive standardized fashion. OBEX uses a client- server model and is independent of the transport mechanism and transport API. The OBEX protocol also defines a folder-listing object, which is used to browse the contents of folders on remote device. RFCOMM is used as the main transport layer for OBEX. Content formats The formats for transmitting vCard and vCalendar information are also defined in the Bluetooth specification. The formats do not define transport mechanisms but the format in which electronic business cards and personal calendar entries and scheduling information are transported. vCard and vCalendar is transferred by OBEX. Wireless Application Protocol, WAP The Wireless Application Protocol (WAP) is a wireless protocol specification that works across a variety of wide-area wireless network technologies bringing the Internet to mobile devices. Bluetooth can be used like other wireless networks with regard to WAP, it can be used to provide a bearer for transporting data between the WAP Client and its adjacent WAP Server. Furthermore, Bluetooth’s ad hoc networking capability gives a WAP client unique possibilities regarding mobility compared with other WAP bearers. The traditional form of WAP communications involves a client device that communicates with a Server/Proxy device using the WAP protocols. Bluetooth is expected to provide a bearer service as specified by the WAP architecture. The WAP technology supports server push. If this is used over Bluetooth, it opens new possibilities for distributing information to handheld devices on location basis. For example, shops can push special price offers to a WAP client when it comes within Bluetooth range. CONCLUSION: A new global standard for voice, data also the devices are wireless so portability issue is removed.Eliminates use of cables and need of connecting every device with cables.Low power, low range, low cost network device so use becomes reasonable.Further improvements are planned to made in Bluetooth are data rate, power reduction, range. Acknowledgement: I will like to thank our Prof. for giving the chance to explore oneself. References: [1].http://www.tech.plym.ac.uk/dcee/postgrad/refer ence/BlueTooth/page2.html#architecture [2].http://www.althos.com/tutorial/Bluetooth- tutorial-protocol-layers.html [3].http://www.bluetooth.com/Pages/Bluetooth- Home.aspx [4].http://www.palowireless.com/infotooth/tutorial. asp [5].http://en.wikipedia.org/wiki/Bluetooth_protocol s [6].http://msdn.microsoft.com/en- us/library/ms890956.aspx [7].http://www.thestudymaterial.com/presentation- seminar/electronics-presentation/51-bluetooth- technology.html?start=3 [8]http://www.scribd.com/doc/135626916/Bluetoot h-Protocol-Stack