【正文】 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). Inorder 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 munications (RFCOMM) is a cable replacement protocol used to create a virtual serial data stream. RFCOMM provides for binary data transport and emulates EIA232 (formerly RS232) 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 mands, as well as being a transport layer for OBEX over Bluetooth. ? Telephony control protocols (TCP). Telephony control protocolbinary (TCS BIN) is the bitoriented protocol that defines the call control signaling for the establishment of voice and data calls between Bluetooth devices. Additionally, TCS BIN defines mobility management procedures for handling groups of Bluetooth TCS devices. TCSBIN 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 standardsmaking anizations and incorporated into Bluetooth’s protocol stack, allowing Bluetooth to create protocols only when necessary. The adopted protocols include: ? PointtoPoint Protocol (PPP): Inter standard protocol for transporting IP datagrams over a pointtopoint link. ? TCP/IP/UDP: For municating with the device connected to Inter. ? Object Exchange Protocol (OBEX): Sessionlayer protocol for the exchange of objects, providing a model for object and operation representation. It uses the clientserver 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 to GHz, using a spread spectrum, frequency hopping, fullduplex signal at a nominal rate of 1600 hops/sec. The 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 municate 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 bee 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 connectionoriented synchronous link (SCO) and connectionlessoriented 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 munication: as to SCO link, 1/3 FEC is used。 Bluetooth may not actually deal streaming video or highquality pictures and audio at this end, except this possibly will alter in the future when fresh Bluetooth standards are initiated. Simple and Competent to Utilize Creating and configur