LOGICAL LINK CONTROL AND ADAPTATION PROTOCOL

               The logical link control and adaptation protocol or L2CAP is equivalent to the LLC sub layer in LAN's . It is used for data exchange on an ACL link . SCO channel do not use L2CAP .The below fig : shows the format of the data packet at this level .

1. The length field in the data packet represents the size of the data , coming from the upper layers . This length field is 2 - bytes .
2. The maximum data , it can support is 65,535 bytes .
3. The unique identifier for the virtual channel created at this level is defined by channel ID.

                The L2CAP ha specific duties : Multiplexing , Segmentation and Reassembly , Quality of service , and group management .

MULTIPLEXING:-    
                     This layer handles multiplexing and de-multiplexing of packets from different upper layer sources . The L2CAP can multiplexing . At the sender site , it accepts data from one of the upper - layer protocols , frames them , and delivers them to the base band layer . At the receiver site , it accepts a frame from the base band layer , extracts the data , and delivers them to the appropriate protocol layer .

SEGMENTATION AND REASSEMBLY:-  

                                             The maximum size of the payload field in the base band layer is 2774 bits , or 343 bytes . This includes 4 bytes to define the packet and packet length , so the size of the packet that can arrive from an upper layer can only be 339 bytes . The L2CAP divides these large packets into smaller segments and add extra i/f to define the location of the segments in the original packet . The L2CAP segments the packet at the source and reassembles them at the destination .

GROUP MANAGEMENT:-

                                       Another functionality of L2CAP is to allow devices to create a type of logical addressing between themselves . This is similar to multi casting .

QUALITY OF SERVICE:-

                                         This layer is responsible for quality of service when the link is in establishing state or when the link is in normal state of operation .

                                  

                                    

   

MULTIPLE - SECONDARY COMMUNICATION

• The process is a little more involved if there is more than one secondary in the piconet . The primary uses the even - numbered slots but a secondary sends in the next odd - numbered slot if the packet in the previous slot was addressed to it .
• All secondaries listen on even - numbered slots , but only one secondary sends in any odd - numbered slot as shown below:

1. In slot 0 , the primary sends a frame to secondary 1 .
2. In slot 1 , only secondary 1 sends a frame to the primary because the previous frame was addressed to secondary 1 ; other secondaries are silent .
3. In slot 2 , the primary sends a frame to secondary 2 .
4. In slot 3 , only secondary 2 send a frame to primary because the previous frame was addresses to secondary 2 ; other secondaries are silent .
5. The cycle continues .

                  This access method is similar to a poll / select operation with reservation . When the primary selects secondary , it also polls it .

                     The next time slot is reserved for the polled station to send its frame , if the polled secondary has no frame to send , the channel is silent .

                       Each frame is transmitted over a logical channel , called a LINK , between master and a slave . Two types of links can exist:

                                                                      1. Synchronous connection oriented link( SCO )

                                                                      2. Asynchronous connection link( ACL )

Synchronous Connection Oriented (SCO):-

•  The other is the SCO link , for real - time data , such as telephone connections .
• SCO link is used when avoiding latency (delay in data delivery) is more important than integrity .
• SCO link , a physical link is created between the primary and a secondary by reserving specific slots at regular intervals . The basic unit of connection is 2 slots , one foe each direction .
• If a packet is damaged , it is never re transmitted . This type of channel is allocated a fixed slot in each direction . Due to the time - critical nature of SCO links , frames sent over them are never re transmitted . Instead , forward error correction can be used to provide high reliability .
• A slave may have up to three SCO links with its master . Each SCO link can transmit one 64 Mbps PCM audio channel .

Asynchronous Connection - Less(ACL) :-

• The first is the ACL link , which is used for packet - switched data available at irregular intervals .
• These data come from the L2CAP layer on the sending side and are delivered to the L2CAP layer on the receiving side .
• ACL traffic is delivered on a best efforts basis . No guarantees are given .
• Frames can be lost and may have to be re transmitted . A slave may have only one ACL link to its master .

SINGLE - SECONDARY COMMUNICATION

•  If the piconet has only one secondary , the TDMA operation is very simple . The time is divided into slots of 625 microseconds .
• The primary / master uses even - numbered slots (0,2,4,....); the secondary / slave uses odd - numbered slots  (1,3,5,.......) .
• TDD- TDMA allows the primary and secondary to communicate in half - duplex mode .
•  In slot 0 , the primary sends , and the secondary receivers; in slot 1 , the secondary sends, and the primary receives . 

BLUETOOTH LAYER

              Bluetooth layer uses several layers that do not exactly match those of the internet model . The below fig shows these layers ,

• The bottom layer is the physical radio layer , which is corresponds to the physical layer in the OSI and 802 models . It deals with radio transmission and modulation .
• The base band layer is  somewhat similar to the MAC sub layer but also includes elements of the physical layer . It deals with how master controls time slots and how these slots are groped into frames .
• The link manager handles the establishment of logical channels between devices , including power management , authentication , and quality of service .
• The logical link control adaptation protocol shields the upper layers from the details of transmission . It is analogous to the standard 802 LLC sub layer , but technically different from it .
• The next layer up is the middle ware layer , which contains a mix of different protocols . The 802 LLC was inserted here by IEEE for compatibility with its other 802 networks  .
• The RF comm , telephony , and service discovery protocols are native . RF comm(Radio frequency communication) is the protocol that emulates the standard serial port found on PCs for connecting the keyboard , mouse , and modem , among other devices . It has been designed to allow legacy devices to use it easily .
• The telephony protocol is a real time protocol used for the three speech oriented profiles . It also manages call setup and termination . Finally , the service discovery protocol is used to locate services within the network .
• The top layer is where the applications and profiles are located . They make use of the protocols in lower layers to get their work done . Each application has its own dedicated subset of the protocols . Specific devices , such as a headset , usually contain only those protocols needed by that application and no others . 

RADIO LAYER:-

• The radio layer moves the bits from master to slave , or vice versa . It is a low power system with a range of meters operating in the 2.4-GHz ISM band . The band is divided into 79 channels of L MHz each .
• Bluetooth uses the frequency - hopping spread spectrum (FHSS) method in the physical layer to avoid interference from other devices or other networks .
• Bluetooth hops 1600 times per second , which means that each device changes its modulation frequency 1600 times per second .
• A device uses a frequency for only 625 micro seconds (1/1600 s) before it hops to another frequency; the dwell times is 625 microseconds .
• To transform bits to a signal , Bluetooth uses a sophisticated version of FSK called GFSK (FSK with Gaussian bandwidth filtering) . GFSK has a carrier frequency .
• Bit 1 is represented by a frequency deviation above the carrier; bit 0 is represented by a frequency deviation below the carrier .
•  The frequencies , in MHz are defined according to the following formula for each channel:           Fc = 2402+n                    where n= 0,1,2,3,............,78 .

                   

                             For example : the 1st channel uses carrier frequency 2402 MHz (2.402 GHz) , and the 2nd channel uses carrier frequency 2403 MHz (2.403 GHz) .

BASE BAND LAYER :-

• The base band layer is roughly equivalent to the MAC sub layer in LAN's . It turns the raw bit stream into frames and defines some key formats .
• The primary/ master and secondary/ slaves communicate with each other using time slots. The length of a time slot is exactly the same as the dwell time , 625 microseconds this means during the time that one frequency is used , a sender sends a frame to a secondary is a secondary sends a frame to the primary .
• The communication is only b,w the primary and a secondary; secondary's cannot communicate directly with one another . The master's transmissions starting in the even slots and the slave's transmissions starting in the odd ones .
• Bluetooth uses a form of TDMA that is called TDD - TDMA (TIME DIVISION DUPLEX TDMA) is a kind of half - duplex communication in which the secondary and receiver send and receiver data , but not at the same time (half - duplex)

BLUETOOTH ARCHITECTURE

                             Bluetooth defines two types of network:

                                    a) Piconet

                                    b) Scatternet

•  Bluetooth is a packet-based protocol with a master-slave structure. One master may communicate with up to 7 slaves in a piconet, all devices share the master's clock.
• Whenever there is a connection between two Bluetooth devices, a piconet is formed . Any Bluetooth device can be either a master or a slave. All devices have the same timing and frequency hopping sequence.
• A Bluetooth  network is called a PICONET or a slave. All devices have the stations, one of which is called PRIMARY and the rest are called SECONDRIES .
• The communication between  the primary and the secondary can be one- to -one or one-to-many. 
  

• A piconet can have maximum of 7 secondaries must be active state an additional 8 secondary's can be in the parked state.
• A secondary in a parked state is synchronized with the primary but cannot take part in communication until it is moved from the parked state means that an active station must go to the parked state.
• Multiple piconets can exist in the large room and can even be connected via a bridge node.

• The master chooses which slave device to address , it switches rapidly from one device to another in a round-robin fashion. Since it is the master that chooses which slave to address , whereas a slave is supposed to listen in each receive slot.
• Being a master of seven slaves is possible; being a slave of more than one master is difficult.

SCATTER NET:-

• An interconnected collection of piconets is called a SCATTERNET .
• A secondary station in one piconet can be the primary in another piconet . This station can receive messages from the primary in the piconet and acting as a primary , delivery them to secondaries in the second piconet.
• A station can be a member of two piconets.

 

BLUETOOTH

  In 1994, the L. M . Ericsson company became interested in connecting its mobile phones to other devices (e.g., PDAs) without cables. Together with four other companies (IBM, Intel,Nokia, and Toshiba) , it formed a Special interest group, to develop a wireless standard for interconnecting computing and communication devices and accessories using short-range , low-power , inexpensive wireless radios . The project was named Bluetooth.
       

           Bluetooth:- Bluetooth is a wireless technology standard for exchanging data over short distances using short - wavelength radio transmissions in the ISM band from 2400-2480 MHz from fixed and mobile devices, creating personal area networks with high levels of security . It can connect several devices, overcoming problems of synchronization.

                     Bluetooth operates in the range of 2400-2483.5 MHz (including guard bands). This is in the globally unlicensed industrial , scientific and medical (ISM) 2.4 GHz short-range radio frequency band.

                      It was named for HaraldBlaatand , the king of Denmark (940-981), a viking king who unified (i.e., conquered) Denmark and Norway Blaatand translates to Bluetooth , also without cables.

                      Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones , notebooks, computer (desktop and laptop), cameras , printers and so on.

                           Bluetooth technology has several applications. Peripheral devices such as wire less mouse or keyboard can communicate with the computer through this technology.

                        Today , Bluetooth technology is the implementation of a protocol defined by the IEEE 802.15 standard. The standard defines a wireless personal -area network operable in an area the size of a room or a hall.

                                          

INTRODUCTION

                        

                                       One of the fastest growing technologies in communication field is wireless communication . The demand for wireless communication is increasing everywhere because it does not require cables for connecting devices. These wireless devices can be found in places like office buildings, college campuses and in many public areas.

                                           One of the technologies for small wireless LAN is bluetooth . Wireless technology is also used in cellular telephony and satellite networks.