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CS601 Wireless Communication and Networks Unit - III

MTech CSE (PT, 2011-14) SRM, Ramapuram 1 hcr:innovationcse@gg

UNIT – III WIRELESS LANS Wireless LAN Technology-IEEE 802.11 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 802.11)

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



Infrastructure and ad-hoc networks

Example of three infrastructure-based wireless networks

802.11, HyperLAN

Example of two ad-hoc wireless networks

Bluetooth

IEEE 802.11 System architecture

Protocol architecture

Physical layer

Medium access control layer

MAC management



System architecture

Protocol architecture

stations (STAi)

access points (AP)

basic service set (BSSi)

distribution system

extended service set (ESS)

distribution system services

Adhoc

o Independent BSSs (IBSS)

PHY

physical layer convergence protocol (PLCP)

physical medium dependent sublayer (PMD)

MAC

medium access, fragmentation of user data, and

encryption



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 802.11 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 802.11 PHY frame using DSSS

Infra red

based on infra red (IR) transmission, uses near visible light at 850–950 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



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



IEEE 802.11 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 802.11 hidden node provisions for contention-free access

IEEE 802.11 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.



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 802.11 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 1100. 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



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 802.11 infrastructure network

AP always tries to schedule transmissions according to the expected beacon interval (target beacon

transmission time)

Beacon transmission in a busy 802.11 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



Power management

The basic idea of IEEE 802.11 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 802.11 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 802.11 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.



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 802.11a

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 802.11b

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

802.11e (MAC enhancements)

802.11f (Inter-Access Point Protocol)

802.11g (Data rates above 20 Mbit/s at 2.4 GHz)

802.11h (Spectrum managed 802.11a)

o balance the load in the 5 GHz band

802.11i (Enhanced Security mechanisms)

o stronger encryption and authentication mechanisms



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 5.1-5.3GHz 17.2-17.3GHz

Topology decentralized ad-

hoc/infrastructure

cellular,

centralized

point-to-

multipoint

point-to-point

Antenna omni-directional directional

Range 50 m 50-100 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



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: 5.1764680 GHz



o optional (not allowed in all countries)





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



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: 11111010100010011100000110010110

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 IES = 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 PE(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 IESV = 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 IYS = 168 high rate bit-periods.

The length of an individual yield listening period can be 0 to 9 slots

The probability PY(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



BLUETOOTH

Topics

Introduction

User scenarios

Architecture

Radio layer

Baseband layer

Link manager protocol

L2CAP

Security

SDP

Profiles

IEEE 802.15

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



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



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



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).



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



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)



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



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



IEEE 802.15

IEEE working group for Wireless Personal Area Networks (WPAN)

IEEE 802.15.1

o standardizes the lower layers of Bluetooth together with the Bluetooth consortium

o focus only on the physical and data link layer

IEEE 802.15.2:

o focus on the coexistence of wireless personal area networks (WPAN) and wireless local area networks

o proposes adaptive frequency hopping

IEEE 802.15.3

o standard providing data rates of 20 Mbit/s or greater while still working with low-power at low-cost.

IEEE 802.15.4

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



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 [email protected]

Date post:	25-Jun-2020
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