CS601 Wireless Communication and Networks. Wireless LAN Technology-IEEE Standards-HIPER LAN and Bluetooth-Role of Wireless local loops.

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1 UNIT III WIRELESS LANS Wireless LAN Technology-IEEE Standards-HIPER LAN and Bluetooth-Role of Wireless local loops. WIRELESS LAN TECHNOLOGY Advantages of WLAN Flexibility Planning o Ad-hoc networks without previous planning possible Design o (almost) no wiring difficulties (e.g. historic buildings, firewalls) Robustness o more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug Cost Disadvantages of WLAN Quality of service o typically very low bandwidth compared to wired networks (1-10 Mbit/s) Proprietary solutions o many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE ) Restrictions o products have to follow many national restrictions, very long time to establish global like, e.g., IMT-2000 Safety and security Design Goals for WLAN Global operation Low power License-free operation Robust transmission technology Simplified spontaneous cooperation Easy to use Protection of investment Safety and security Transparency for applications Comparison of Infrared vs. Radio transmission Infrared uses IR diodes, diffuse light, multiple reflections (walls, furniture etc.) Advantages simple, cheap, available in many mobile devices no licenses needed simple shielding possible Disadvantages interference by sunlight, heat sources etc. many things shield or absorb IR light low bandwidth Example IrDA (Infrared Data Association) interface available everywhere Radio typically using the license free ISM band at 2.4 GHz Advantages experience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.) Disadvantages very limited license free frequency bands shielding more difficult, interference with other electrical devices Example WaveLAN, HIPERLAN, Bluetooth MTech CSE (PT, ) SRM, Ramapuram 1

2 Infrastructure and ad-hoc networks Example of three infrastructure-based wireless networks , HyperLAN Example of two ad-hoc wireless networks Bluetooth IEEE System architecture Protocol architecture Physical layer Medium access control layer MAC management MTech CSE (PT, ) SRM, Ramapuram 2

3 System architecture stations (STAi) access points (AP) basic service set (BSSi) distribution system extended service set (ESS) distribution system services Adhoc o Independent BSSs (IBSS) Protocol architecture PHY physical layer convergence protocol (PLCP) physical medium dependent sublayer (PMD) MAC medium access, fragmentation of user data, and encryption MTech CSE (PT, ) SRM, Ramapuram 3

4 Physical layer one layer based on infra red o Infra red two layers based on radio transmission o Frequency hopping spread spectrum o Direct sequence spread spectrum Frequency hopping spread spectrum Format of an IEEE PHY frame using FHSS Start frame delimiter (SFD), PLCP_PDU length word (PLW), PLCP signalling field (PSF), Header Error Check Direct sequence spread spectrum Format of an IEEE PHY frame using DSSS Infra red based on infra red (IR) transmission, uses near visible light at nm does not require a line-of-sight between sender and receiver, but should also work with diffuse light The maximum range is about 10 m e.g., classrooms, meeting rooms etc Medium access control layer (MAC) Medium access and inter-frame spacing Traffic services o Asynchronous Data Service (mandatory) exchange of data packets based on best-effort support of broadcast and multicast implemented using Distributed Coordination Function (DCF) o Time-Bounded Service (optional) implemented using Point Coordination Function (PCF) Access methods o DFWMAC-DCF CSMA/CA (mandatory) collision avoidance via randomized back-off mechanism minimum distance between consecutive packets MTech CSE (PT, ) SRM, Ramapuram 4

5 ACK packet for acknowledgements (not for broadcasts) o DFWMAC-DCF w/ RTS/CTS (optional) Distributed Foundation Wireless MAC avoids hidden terminal problem o DFWMAC- PCF (optional) access point polls terminals according to a list The MAC mechanisms are also called distributed foundation wireless medium access control (DFWMAC) Short inter-frame spacing (SIFS), PCF inter-frame spacing (PIFS), DCF inter-frame spacing (DIFS) PIFS < SIFS < DIFS Basic DFWMAC-DCF using CSMA/CA station ready to send starts sensing the medium (CS based on CCA, Clear Channel Assessment) if the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending if the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time) if another station occupies the medium during this, the back-off timer stops (fairness) Basic DFWMAC DCF with several competing senders Station3 has the first request senses the medium, waits for DIFS and accesses the medium Station1, station2, and station5 have to wait at least until the medium is idle for DIFS again after station3 has stopped sending. Exponential backoff algorithm Each time a collision occurs, the contention window doubles up to a maximum MTech CSE (PT, ) SRM, Ramapuram 5

6 IEEE unicast data transfer receiver answers directly with an acknowledgement (ACK). The receiver accesses the medium after waiting for a duration of SIFS so no other station can access the medium in the meantime and cause a collision DFWMAC-DCF with RTS/CTS extension request to send (RTS), net allocation vector (NAV), clear to send (CTS), IEEE hidden node provisions for contention-free access IEEE fragmentation of user data DFWMAC-PCF with polling To provide a time-bounded service, the standard specifies a point coordination function (PCF) on top of the standard DCF mechanisms The point co-ordinator in the access point splits the access time into super frame periods A super frame comprises a contentionfree period and a contention period After the medium has been idle until t1, the point coordinator has to wait for PIFS to access the medium The point coordinator now sends data D1 downstream to the first wireless station After waiting for SIFS again, the point coordinator can poll the second station by sending D2. This station may answer upstream to the coordinator with data U2. MTech CSE (PT, ) SRM, Ramapuram 6

7 Polling continues with the third node. This time the node has nothing to answer and the point coordinator will not receive a packet after SIFS After waiting for PIFS, the coordinator can resume polling the stations. Finally, the point coordinator can issue an end marker (CFend), indicating that the CP may start again MAC frames IEEE MAC packet structure Frame control o Protocol version: 0 o Type: Function of the frame : management (00), control (=01), or data (=10). value 11 is reserved o Subtype: subtypes for management frames are: 0000 for association request, 1000 for beacon. RTS is a control frame with subtype 1011, CTS is coded as User data is transmitted as data frame with subtype 0000 o Wired equivalent privacy (WEP): Duration/ID o period of time in which the medium is occupied (in μs) Address 1 to 4 o standard IEEE 802 MAC addresses (48 bit each) Sequence control o used to filter duplicates Data: max. 2,312 byte MTech CSE (PT, ) SRM, Ramapuram 7

8 MAC Management Synchronization o Functions to support finding a WLAN, synchronization of internal clocks, generation of beacon signals. Power management o Functions to control transmitter activity for power conservation, o e.g., periodic sleep, buffering, without missing a frame. Roaming o Functions for joining a network (association), changing access points, scanning for access points. Management information base (MIB) o All parameters representing the current state of a wireless station and an access point are stored within a MIB for internal and external access. o A MIB can be accessed via standardized protocols such as the simple network management protocol (SNMP). Synchronization timing synchronization function (TSF) A beacon contains a timestamp and other management information Beacon transmission in a busy infrastructure network AP always tries to schedule transmissions according to the expected beacon interval (target beacon transmission time) Beacon transmission in a busy ad-hoc network each node maintains its own synchronization timer and starts the transmission of a beacon frame after the beacon interval All other stations now adjust their internal clocks according to the received beacon and suppress their beacons for this cycle If collision occurs, the beacon is lost MTech CSE (PT, ) SRM, Ramapuram 8

9 Power management The basic idea of IEEE power management is to switch off the transceiver whenever it is not needed two states for a station: sleep and awake Power management in IEEE infrastructure networks With every beacon sent by the access point, a traffic indication map (TIM) is transmitted. The TIM contains a list of stations for which unicast data frames are buffered in the access point. the AP maintains a delivery traffic indication map (DTIM) interval for sending broadcast/multicast frames Power management in IEEE ad-hoc networks Destinations are announced using ad-hoc traffic indication map (ATIMs) the announcement period is called the ATIM window Roaming Moving between access points is called roaming The steps for roaming between access points are A station decides that the current link quality to its access point AP1 is too poor. The station then starts scanning for another access point. Scanning involves the active search for another BSS and can also be used for setting up a new BSS in case of ad-hoc networks. MTech CSE (PT, ) SRM, Ramapuram 9

10 o Passive scanning simply means listening into the medium to find other networks, i.e., receiving the beacon of another network issued by the synchronization function within an access point. o Active scanning comprises sending a probe on each channel and waiting for a response. Beacon and probe responses contain the information necessary to join the new BSS. The station then selects the best access point for roaming based on, e.g., signal strength, and sends an association request to the selected access point AP2. The new access point AP2 answers with an association response. If the response is successful, the station has roamed to the new access point AP2. Otherwise, the station has to continue scanning for new access points. The access point accepting an association request indicates the new station in its BSS to the distribution system (DS). The DS then updates its database, which contains the current location of the wireless stations Additionally, the DS can inform the old access point AP1 that the station is no longer within its BSS. Future developments IEEE a o compatible MAC, but now 5 GHz band o transmission rates up to 20 Mbit/s o close cooperation with BRAN (ETSI Broadband Radio Access Network) IEEE b o higher data rates at 2.4 GHz o proprietary solutions already offer 10 Mbit/s IEEE WPAN (Wireless Personal Area Networks) o market potential o compatibility o low cost/power, small form factor o technical/economic feasibility Bluetooth e (MAC enhancements) f (Inter-Access Point Protocol) g (Data rates above 20 Mbit/s at 2.4 GHz) h (Spectrum managed a) o balance the load in the 5 GHz band i (Enhanced Security mechanisms) o stronger encryption and authentication mechanisms MTech CSE (PT, ) SRM, Ramapuram 10

11 HIPER LAN HIgh PERformance Local Area Network ETSI standard o European standard, cf. GSM, DECT,... o Enhancement of local Networks and interworking with fixed networks o integration of time-sensitive services from the early beginning HIPERLAN family o one standard cannot satisfy all requirements o range, bandwidth, QoS support o commercial constraints o HIPERLAN 1 standardized since 1996 HIPERLAN protocol family HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4 Application wireless LAN access to ATM fixed networks wireless local loop point-to-point wireless ATM connections Frequency GHz GHz Topology cellular, centralized decentralized adhoc/infrastructure point-tomultipoint point-to-point Antenna omni-directional directional Range 50 m m 5000 m 150 m QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR) Mobility <10m/s stationary Interface conventional LAN ATM networks Data rate 23.5 Mbit/s >20 Mbit/s 155 Mbit/s Power conservation yes not necessary HIPERLAN 1 Characteristics Data transmission o point-to-point, point-to-multipoint, connectionless o 23.5 Mbit/s, 1 W power, 2383 byte max. packet size Services o asynchronous and time-bounded services with hierarchical priorities o compatible with ISO MAC MTech CSE (PT, ) SRM, Ramapuram 11

12 Topology o infrastructure or ad-hoc networks o transmission range can be larger then coverage of a single node ( forwarding integrated in mobile terminals) Further mechanisms o power saving, encryption, checksums HIPERLAN 1 - Services and protocols CAC service o definition of communication services over a shared medium o specification of access priorities o abstraction of media characteristics MAC protocol o MAC service, compatible with ISO MAC and ISO MAC bridges o uses HIPERLAN CAC CAC protocol o provides a CAC service, uses the PHY layer, specifies hierarchical access mechanisms for one or several channels Physical protocol o send and receive mechanisms, synchronization, FEC, modulation, signal strength HIPERLAN layers, services, and protocols HIPERLAN 1 - Physical layer Scope o modulation, demodulation, bit and frame synchronization o forward error correction mechanisms o measurements of signal strength o channel sensing Channels o 3 mandatory and 2 optional channels (with their carrier frequencies) o mandatory channel 0: GHz channel 1: GHz channel 2: GHz o optional (not allowed in all countries) MTech CSE (PT, ) SRM, Ramapuram 12

13 channel 3: GHz channel 4: GHz HIPERLAN 1 - Physical layer frames Maintaining a high data-rate (23.5 Mbit/s) is power consuming - problematic for mobile terminals o packet header with low bit-rate comprising receiver information o only receiver(s) address by a packet continue receiving Frame structure o LBR (Low Bit-Rate) header with 1.4 Mbit/s o 450 bit synchronization o minimum 1, maximum 47 frames with 496 bit each o for higher velocities (> 1.4 m/s) the maximum number of frames has to be reduced Modulation o GMSK for high bit-rate, FSK for LBR header HIPERLAN 1 - CAC sublayer Channel Access Control (CAC) o assure that terminal does not access forbidden channels o priority scheme, access with EY-NPMA Priorities o 5 priority levels for QoS support o QoS is mapped onto a priority level with the help of the packet lifetime (set by an application) if packet lifetime = 0 it makes no sense to forward the packet to the receiver any longer standard start value 500ms, maximum 16000ms if a terminal cannot send the packet due to its current priority, waiting time is permanently subtracted from lifetime based on packet lifetime, waiting time in a sender and number of hops to the receiver, the packet is assigned to one out of five priorities the priority of waiting packets, therefore, rises automatically HIPERLAN 1 - EY-NPMA (MAC Layer) EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access) 3 phases: priority resolution, contention resolution, transmission finding the highest priority o every priority corresponds to a time-slot to send in the first phase o higher priorities can not be preempted o if an earlier time-slot for a higher priority remains empty, stations with the next lower priority might send o after this first phase the highest current priority has been determined Phases of the HIPERLAN 1 EY-NPMA access scheme MTech CSE (PT, ) SRM, Ramapuram 13

14 EY-NPMA divides the medium access of different competing nodes into three phases: Prioritization: Determine the highest priority of a data packet ready to be sent by competing nodes. Contention: Eliminate all but one of the contenders Transmission: Finally, transmit the packet of the remaining node. Prioritization phase offers five different priorities for data packets ready to be sent objective of the prioritization phase is to make sure that no node with a lower priority gains access to the medium while packets with higher priority are waiting at other nodes priority detection, time is divided into five slots, slot 0 (highest priority) to slot 4 (lowest priority). Each slot has a duration of IPS = 168 high rate bit-periods. If a node has the access priority p, it has to listen into the medium for p slots (priority detection). If the node senses the medium is idle for the whole period of p slots, the node asserts the priority by immediately transmitting a burst for the duration IPA = 168 high rate bit-periods (priority assertion). The burst consists of the following high rate bit sequence, which is repeated as many times as necessary for the duration of the burst: If the node senses activity in the medium, it stops its attempt to send data in this transmission cycle and waits for the next one. The whole prioritization phase ends as soon as one node asserts the access priority with a burst. This means that the prioritization phase is not limited by a fixed length, but depends on the highest priority.. Elimination phase time is divided into slots, using the elimination slot interval I ES = 212 high rate bit periods. The length of an individual elimination burst is 0 to 12 slot intervals long, the probability of bursting within a slot is 0.5. The probability P E (n) of an elimination burst to be n elimination slot intervals long is given by The elimination phase now resolves contention by means of o elimination bursting o elimination survival verification. Each contending node sends an elimination burst with length n as determined via the probabilities and then listens to the channel during the survival verification interval I ESV = 256 high rate bit periods. The burst sent is the same as for the priority assertion. A contending node survives this elimination phase if, and only if, it senses the channel is idle during its survival verification period. One or more nodes will survive this elimination phase, and can then continue with the next phase Yield phase the remaining nodes only listen into the medium without sending any additional bursts Time is divided into yield slots with a duration of I YS = 168 high rate bit-periods. The length of an individual yield listening period can be 0 to 9 slots The probability P Y (n) for a yield listening period to be n slots long is 0.1 for all n, 0 n 9. Each node now listens for its yield listening period. If it senses the channel is idle during the whole period, it has survived the yield listening. Otherwise, it withdraws for the rest of the current transmission cycle. at this point there can still be more than one surviving node so a collision is still possible Transmission phase A node that has survived the prioritization and contention phase can now send its data, called a Low Bit- Rate High Bit-Rate HIPERLAN 1 CAC Protocol Data Unit (LBR-HBR HCPDU). In case of a unicast transmission, the sender expects to receive an immediate acknowledgement from the destination, called an acknowledgement HCPDU (AK-HCPDU), which is an LBR HCPDU containing only an LBR part MTech CSE (PT, ) SRM, Ramapuram 14

15 BLUETOOTH Topics Introduction User scenarios Architecture Radio layer Baseband layer Link manager protocol L2CAP Security SDP Profiles IEEE Introduction ad-hoc piconets o local area networks with a very limited coverage and without the need for an infrastructure o different type of network is needed to connect different small devices in close proximity (about 10 m) without expensive wiring or the need for a wireless infrastructure gross data rate is 1 Mbit/s Bluetooth consortium o Founded by Ericsson, Intel, IBM, Nokia, Toshiba o goal of developing a single-chip, low-cost, radio-based wireless network technology Wireless Personal Area Networks (WPAN) Criteria o Market potential o Compatibility o Distinct identity o Technical feasibility o Economic feasibility User scenarios Connection of peripheral devices o keyboard, mouse, joystick, headset, speakers o no wires are needed for data transmission Support of ad-hoc networking o students might join a lecture, with the teacher distributing data to their PDAs Bridging of networks Example configurations with a Bluetooth-based piconet MTech CSE (PT, ) SRM, Ramapuram 15

16 Architecture Networking Piconet a collection of Bluetooth devices which are synchronized to the same hopping sequence One device can act as master (M), all other devices connected to the master must act as slaves (S). parked devices (P) o can not actively participate in the piconet (i.e., they do not have a connection), but are known and can be reactivated within some milliseconds Devices in stand-by (SB) do not participate in the piconet. Each piconet has exactly one master and up to seven simultaneous slaves. More than 200 devices can be parked. The reason for the upper limit of eight active devices, is the 3-bit address used in Bluetooth. Formation of a piconet. As all active devices have to use the same hopping sequence they must be synchronized. The first step involves a master sending its clock and device ID. The hopping pattern is determined by the device ID, a 48-bit worldwide unique identifier All active devices are assigned a 3-bit active member address (AMA). All parked devices use an 8-bit parked member address (PMA) Bluetooth scatternet As more users join the piconet, the throughput per user drops quickly groups of piconets is called a scatternet Bluetooth applies FH-CDMA for separation of piconets. all piconets can share the total of 80 MHz bandwidth available Communication between different piconets takes place by devices jumping back and forth between nets MTech CSE (PT, ) SRM, Ramapuram 16

17 Protocol Stack Can be divided into the following two A Core Specification (Bluetooth, 2001a) o describes the protocols from physical layer to the data link control together with management functions o The core protocols of Bluetooth comprise the following elements: o Radio Specification of the air interface, i.e., frequencies, modulation, and transmit power o Baseband Description of basic connection establishment, packet formats, timing, and basic QoS parameters o Link manager protocol Link set-up and managmnt between devices including security functions and parameter negotiation o Logical link control and adaptation protocol (L2CAP) Adaptation of higher layers to the baseband (connectionless and connection-oriented services o Service discovery protocol Device discovery in close proximity plus querying of service characteristics Profile Specifications (Bluetooth, 2001b) o describes many protocols and functions needed to adapt the wireless Bluetooth technology to legacy and new applications Cable Replacement Protocol RFCOMM emulates a serial line interface following the EIA (RS) -232 allows replacement of serial line cables enables many legacy applications and protocols to run over Bluetooth. supports multiple serial ports over a single physical channel Telephony Control protocol Specification Binary (TCS BIN) describes a bit-oriented protocol that defines call control signaling for the establishment of voice and data calls between Bluetooth devices. It also describes mobility and group management functions. Adopted protocols MTech CSE (PT, ) SRM, Ramapuram 17

18 Classical Internet applications can still use the standard TCP/IP stack running over PPP or use the more efficient Bluetooth network encapsulation protocol (BNEP). Telephony applications can use the AT modem commands as if they were using a standard modem. Calendar and business card objects (vcalendar/vcard) can be exchanged using the object exchange protocol (OBEX) as common with IrDA interfaces. Audio applications may directly use the baseband layer after encoding the audio signals o A real difference to other protocol stacks Radio Layer Design limitations Bluetooth devices will be integrated into typical mobile devices and rely on battery power. o requires small, low power chips which can be built into handheld devices. Worldwide operation also requires a frequency which is available worldwide. has to support multi-media data for data and voice transmission Design uses the license-free frequency band at 2.4 GHz frequency-hopping/time-division duplex scheme is used for transmission fast hopping rate of 1,600 hops per second. The time between two hops is called a slot, which is an interval of 625 μs. Each slot uses a different frequency. uses 79 hop carriers equally spaced with 1 MHz. transceivers use Gaussian FSK for modulation Available in three classes: o Power class 1 Maximum power is 100 mw and minimum is 1 mw typ. 100 m range without obstacles Power control is mandatory. o Power class 2 Maximum power is 2.5 mw, nominal power is 1 mw, and minimum power is 0.25 mw typ. 10 m range without obstacles Power control is optional. o Power class 3 Maximum power is 1 mw. Baseband Layer performs frequency hopping for interference mitigation and medium access also defines physical links and many packet formats Uses time division duplex (TDD) Frequency selection during data transmission (1, 3, 5 slot packets) 1-slot packets as the data transmission uses one 625 μs slot. Bluetooth also defines 3-slot and 5-slot packets for higher data rates (multi-slot packets). No frequency hopping is performed within packets. Baseband packet format Access code needed for timing synchronization and piconet identification (channel access code, CAC). MTech CSE (PT, ) SRM, Ramapuram 18

19 may represent special codes during paging (device access code, DAC), inquiry (inquiry access code, IAC) consists of a 4 bit preamble, a synchronization field, and a trailer (if a packet header follows). The 64-bit synchronization field is derived from the lower 24 bit of an address (lower address part, LAP). Packet header The 4-bit type field determines the type of the packet. o Packets may carry control, synchronous, or asynchronous data. A simple flow control mechanism for asynchronous traffic uses the 1-bit flow field. o If a packet is received with flow=0 asynchronous data, transmission must stop. o As soon as a packet with flow=1 is received, transmission may resume. Active Member Address, acknowledgement number ARQN, sequence number SEQN Payload Up to 343 bytes payload can be transferred. structure depends on the type of link Physical links Synchronous Connection-Oriented (SCO) link Asynchronous connectionless link (ACL) Synchronous Connection-Oriented (SCO) link o the master reserves two consecutive slots (forward and return slots) at fixed intervals. o A master can support up to three simultaneous SCO links to the same slave or to different slaves. o A slave supports up to two links from different masters or up to three links from the same master Asynchronous Connectionless Link (ACL) master uses a polling scheme. A slave may only answer if it has been addressed in the preceding slot Example data Transmission The master always uses the even frequency slots, the odd slots are for the slaves Error recovery MTech CSE (PT, ) SRM, Ramapuram 19

20 Link Manager Protocol Groups of functions Authentication, pairing, and encryption o control the exchange of random numbers and signed responses Synchronization o Precise synchronization is of major importance within a Bluetooth network. o The clock offset is updated each time a packet is received from the maste Capability negotiation o devices have to agree the usage of, e.g., multi-slot packets, encryption, SCO links, voice encoding, park/sniff/hold mode (explained below), HV2/HV3 packets etc. Quality of service negotiation Power control o Depending on received signal level the device can direct the sender of the measured signal to increase or decrease its transmit power. Link supervision o set up new SCO links, or it may declare the failure of a link. State and transmission mode change o Devices might switch the master/slave role, o detach themselves from a connection, o or change the operating mode Major baseband states of a Bluetooth device Standby o currently not participating in a piconet (and not switched off) inquiry o device wants to establish a piconet or a device just wants to listen to see if something is going on Page o set up connections to each device o continue to page more devices that will be added to the piconet active state o the slave participates in the piconet by listening, transmitting, and receiving. o ACL and SCO links can be used o Either transmit data or are simply connected o A device can enter standby again, via a detach procedure To save battery power, a Bluetooth device can go into one of three low power states: o Sniff state highest power consumption device keeps its AMA. o Hold state The device does not release its AMA but stops ACL transmission o Park state lowest duty cycle and the lowest power consumption device releases its AMA and receives a parked member address (PMA) MTech CSE (PT, ) SRM, Ramapuram 20

21 Logical Link Control and Adaptation Protocol L2CAP data link control protocol on top of the baseband layer offering logical channels between Bluetooth devices with QoS properties available for ACLs only provides three different types of logical channels Connectionless o unidirectional channels are typically used for broadcasts from a master to its slave(s). Connection-oriented o bi-directional and QoS o define average/peak data rate, maximum burst size, latency, and jitter. Signaling o exchanging signaling messages between L2CAP entities. L2CAP packet formats The length field indicates the length of the payload (plus PSM for connectionless PDUs). The CID has the multiplexing/demultiplexing function Protocol/Service multiplexor (PSM) field is needed to identify the higher layer recipient for the payload. Several PSM values have been defined, e.g., 1 (SDP), 3 (RFCOMM), 5 (TCS-BIN). The payload of the signaling PDU contains one or more commands. Each command has its own o code (e.g.,for command reject, connection request, disconnection response etc.) o ID that matches a request with its reply o The length field indicates the length of the data field for this command. Security steps in the security architecture pairing o necessary if two Bluetooth devices have never met before. o To set up trust between the two devices a user can enter a secret PIN into both devices. Authentication MTech CSE (PT, ) SRM, Ramapuram 21

22 o Link key : Based on the PIN, the device address, and random numbers Encryption o Based on the link key, values generated during the authentication, and again a random number an encryption key is generated Ciphering o simple XOR of the user data and the payload key Bluetooth security components and protocols Service Discovery Protocol (SDP) To find new services Devices that want to offer a service have to install an SDP server. For all other devices an SDP client is sufficient Service record., service attribute o attribute ID o attribute value. The attribute value can be an integer, a UUID (universally unique identifier), a string, a Boolean, a URL (uniform resource locator) etc The protocol descriptor list comprises the protocols needed to access this service. Profiles default solutions for a certain usage model. to form a basis for interoperability basic profiles o generic access, service discovery, cordless telephony, intercom, serial port, headset, dialup networking, fax, LAN access, generic object exchange, object push, file transfer, and synchronization. Additional profiles o advanced audio distribution, PAN, audio video remote control, basic printing, basic imaging, extended service discovery, generic audio video distribution, hands-free, and hardcopy cable replacement Each profile selects a set of protocols. o example, the serial port profile needs RFCOMM, SDP, LMP, L2CAP MTech CSE (PT, ) SRM, Ramapuram 22

23 IEEE IEEE working group for Wireless Personal Area Networks (WPAN) IEEE o standardizes the lower layers of Bluetooth together with the Bluetooth consortium o focus only on the physical and data link layer IEEE : o focus on the coexistence of wireless personal area networks (WPAN) and wireless local area networks o proposes adaptive frequency hopping IEEE o standard providing data rates of 20 Mbit/s or greater while still working with low-power at low-cost. IEEE o standardizes low-rate wireless personal area networks (LR-WPAN) o extremely low power consumption enabling multi-year battery life o applications include industrial control and monitoring, smart badges, interconnection of environmental sensors, interconnection of peripherals o data rates between 20 and 250 kbit/s as maximum and latencies down to 15 ms o superframe mode. o a PAN coordinator transmits beacons in predetermined intervals (15 ms 245 s) o three levels of security: no security, access control lists symmetric encryption using AES-128 WIRELESS LOCAL LOOPS (WLL) WLL connects subscribers to local telephone station wirelessly WLL based on Cellular, Satellite, Microcellular Other names RITL (Radio In The Loop) FRA (Fixed Radio Access) WLL Service Desirable Business Related o Call Transfer o Conference Calling COIN Phones v.29 (9600 bps) ISDN (64 kbps) Example Services provided by WLL Marconi WIPLL (Wireless IP Local Loop) Lucent WSS (Wireless Subscriber system) Goodwin WLL MTech CSE (PT, ) SRM, Ramapuram 23

24 Role Of WLL Advantages Cost Less expensive than wired systems the cost of installing KMs of cable is avoided Cost of maintaining the wired infrastructure Installation time Can be installed rapidly challenges getting the permission to use given frequency and finding suitable elevated site Selective installation Radio units are installed only for those who want the service Wired systems requires cable to be laid out in anticipation of subscribers Alternatives to Wired scheme using existing installed cable lack of telephone line to large population lack of quality lines for high-speed applications long distance from central office for xdsl May not have cable TV or cable provided for two way data services Makes WLL as a strong alternative Mobile Cellular technology Cellular systems are too expensive do not provide sufficient facilities less functionaly than broadband WLL As the WLL subscriber unit is fixed, it can use directional antenna pointed at base station antenna, providing improved signal quality in both directions Comments & Feedback Thanks to my family members who supported me while I spent hours and hours to prepare this. Your feedback is welcome at MTech CSE (PT, ) SRM, Ramapuram 24

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