l
Technology
PROTOCOL
The Bluetooth technology standard is set to make different applications can “communicate” with each other. Remote devices in communication use the same protocol stacks, while different applications need different protocol stacks. But, every application needs the data link layer and physical layer of the Bluetooth technology.
The whole Bluetooth protocol stacks is shown as blow. Not any application should use all of the protocols, but one or some lists of these. The chart below shows the relationship between protocols, but the relationship may change in some applications.
The completely protocol stacks include Bluetooth special protocols (like LMP and L2CAP) and not special ones (such as OBEX and UDP). The basic principle for designing protocol and protocol stacks is that use existing high level protocol as possible, ensure the combination of protocols and Bluetooth technology, and take the best advantage of the software and hardware which adapt to the Bluetooth technology standards. The open Bluetooth technology makes device manufacturers can choose protocols freely as they like or used to. The protocols in Bluetooth protocol system
There are four layers in Bluetooth protocol system according to the SIG ? ? ? ?
Core protocols
Cable replacement protocols Telephony control protocols Adopted protocols
Except the protocol layers above, the standard also defines Host/Controller Interface (HCI),which provides command interface for baseband controller, connection manager, hardware state and control register.
Bluetooth core protocols consist of the special protocols made by SIG. Most Bluetooth devices need core protocols, while other protocols are used depend on needs of the application. After all, cable replacement protocols, technology control protocols and adopted protocols based on the core protocols constitute the object-oriented protocols. ? Core protocols ?
LMP (Link Management Protocol)
l
Used for control of the radio link between two devices. Implemented on the controllers.
It identifies and encrypts through launching, exchanging and checking the connection, and decides the size of baseband data packets through conference. It also controls the power mode and work cycle of wireless equipment, and connection status of unit equipment in piconet. ?
L2CAP (Logical Link Control & Adaptation Protocol)
This protocol is used to multiplex multiple logical connections between two devices using different higher level protocols, and provides segmentation and reassembly of on-air packets.
In Basic mode, L2CAP provides packets with a payload configurable up to 64kB, with 672 bytes as the default MTU, and 48 bytes as the minimum mandatory supported MTU.
In Retransmission & Flow Control modes, L2CAP can be configured for reliable or isochronous data per channel by performing retransmissions and CRC checks.
Bluetooth Core Specification Addendum 1 adds two additional L2CAP modes to the core specification. These modes effectively deprecate original Retransmission and Flow Control modes: ?
Enhanced Retransmission Mode (ERTM): This mode is an improved version of the original retransmission mode. This mode provides a reliable L2CAP channel. ?
Streaming Mode (SM): This is a very simple mode, with no retransmission or flow control. This mode provides an unreliable L2CAP channel.
Reliability in any of these modes is optionally and/or additionally guaranteed by the lower layer Bluetooth BDR/EDR air interface by configuring the number of retransmissions and flush timeout (time after which the radio will flush packets). In-order sequencing is guaranteed by the lower layer.
Only L2CAP channels configured in ERTM or SM may be operated over AMP logical links. ?
SDP (Service Discovery Protocol)
Service Discovery Protocol (SDP) allows a device to discover services supported by other devices, and their associated parameters. For example, when connecting a mobile phone to a Bluetooth headset, SDP will be used for determining which Bluetooth profiles are supported by the headset (Headset Profile, Hands Free Profile, Advanced Audio Distribution Profile (A2DP) etc.) and the protocol multiplexer settings needed to connect to each of them. Each service is identified by a Universally Unique Identifier (UUID), with official services (Bluetooth profiles) assigned a short form UUID (16 bits rather than the full 128)/vichitra ? Cable replacement protocols(RFCOMM)
l
Radio frequency communications (RFCOMM) is a cable replacement protocol used to create a virtual serial data stream. RFCOMM provides for binary data transport and emulates EIA-232 (formerly RS-232) control signals over the Bluetooth baseband layer.
RFCOMM provides a simple reliable data stream to the user, similar to TCP. It is used directly by many telephony related profiles as a carrier for AT commands, as well as being a transport layer for OBEX over Bluetooth. ? Telephony control protocols (TCP).
Telephony control protocol-binary (TCS BIN) is the bit-oriented protocol that defines the call control signaling for the establishment of voice and data calls between Bluetooth devices. Additionally, \procedures for handling groups of Bluetooth TCS devices.\
TCS-BIN is only used by the cordless telephony profile, which failed to attract implementers. As such it is only of historical interest.
? Adopted protocols
Adopted protocols are defined by other standards-making organizations and incorporated into Bluetooth’s protocol stack, allowing Bluetooth to create protocols only when necessary. The adopted protocols include: ? ? ?
Point-to-Point Protocol (PPP): Internet standard protocol for transporting IP datagrams over a point-to-point link. TCP/IP/UDP: For communicating with the device connected to Internet.
Object Exchange Protocol (OBEX): Session-layer protocol for the exchange of objects, providing a model for object and operation representation. It uses the client-server mode. ?
Wireless Application Environment/Wireless Application Protocol (WAE/WAP):WAE specifies an application framework for wireless devices and WAP is an open standard to provide mobile users access to telephony and information services.
Technology
SPECTRUM AND INTERFERENCE
Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. The 2.4 GHz ISM band is available and unlicensed in most countries.
SIM frequency band is open to all radio system, So the use of a certain frequency band will meet unpredictable interference sources. Therefore, Bluetooth designs special fast acknowledge and frequency hopping technique to ensure
l
the stability of link. Frequency hopping technique to divide the band into many frequency hopping channels, in a connection, radio transceiver “jump” from a channel to another constantly according to certain code sequence. Only sender and receiver communicate according to this law, and the rest of interference may not press the same rule. The instantaneous bandwidth of Frequency hopping is very narrow, but through the spread spectrum technology it can make the narrow bandwidth one hundred times expanded into wideband, making the influence of interference may become very small. Comparing to other systems that work in the same frequency band, frequency hopping of Bluetooth works faster, data packet of Bluetooth is shorter, which make it more stable than the other ERROR CORRECTION
Bluetooth supports circuit switching and packet switching two techniques, and defines two types of link connection, namely connection-oriented synchronous link (SCO) and connectionless-oriented asynchronous link (ACL)
Bluetooth use three error correction models: 1/3 Forward Error Correction (FEC), 2/3forward Forward Error Correction and Automatic Repeat Request (ARQ). Purpose to the error correction is to reduce the possibility of retransmission, while at the same time increase the extra expenses, but in a reasonable errorless environment, redundant bids will reduce output. So the packet definition itself also keeps flexible ways. Hence the software can be defined whether to adopt FEC. In general, when the channel noise is large, Bluetooth system will uses FEC, in order to ensure the quality of
communication: as to SCO link, 1/3 FEC is used; 2/3 FEC is used in ACL link. In unnumbered ARQ, the data send in a time slot must receive a confirmation of receipt in the next time slot. Only when the data is checked to be without mistake after header error detection and CRC at receiver will the confirmation sent to sender, or an error message will be sent back. RANGE
Range is application specific and although a minimum range is mandated by the Core Specification, there is not a limit and manufacturers can tune their implementation to support the use case they are enabling. Range may vary depending on class of radio used in an implementation: ? ? ? POWER
In order to make a Bluetooth equipment can also be in connection even in a very low power state, Bluetooth stipulates three energy saving state: Park state, Hold state and Sniff state. The energy saving efficiency of these states declines one
Class 3 radios – have a range of up to 1 meter or 3 feet
Class 2 radios – most commonly found in mobile devices , have a range of 10 meters or 33 feet Class 1 radios – used primarily in industrial use cases , have a range of 100 meters or 300 feet
相关推荐：
loading