Bài giảng mạng không dây chương 8 wireless lans, mans and pans

– In infrastructure mode, mobile units communicate through an access point that serves as a bridge to other networks such as Internet or LAN 1/19/22 – Department of Computer Science 13

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Chương 8 Wireless LANs,

MANs and PANs

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Agenda

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1/19/22 – Department of Computer

Science

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data connectivity, but with different

characteristics and expectations and

therefore different market segments

much smaller area (e.g., a building, an office campus, lounges)

formed around the personal operating space

of a user

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Science

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Wireless Local Area Networks (WLANs)

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IEEE 802.11 Standard

standards for indoor LANs (e.g., Ethernet)

WLANs and named it the IEEE 802.11

(now known as IEEE 802.11a)

of 2.4GHz, MAC standard specifies with data rate of 1 or 2 Mbps

compatible product can be manufactured

Science

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IEEE 802.11 Standard

fixed, portable, and moving stations within tens to hundreds of meters

802.11b, IEEE 802.11g, and IEEE

802.11n; their most significant

differences lie in the specification of

the PHY layer.

Science

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IEEE 802.11 Amendments

– Unlicensed National Information

Infrastructure (UNII) 5GHz freq band  less

interference

– Modulation: OFDM with 52 subcarriers

spanning over a 20MHz spectrum

QPSK, 16-QAM, or 64-QAM, depending on

the wireless environment

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IEEE 802.11 Amendments

54Mbps

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Types of WLANs

• The IEEE 802.11 has two basic modes of operation

mode: infrastructure and ad hoc mode

– In ad hoc mode, mobile units transmit directly peer-to-peer

– In infrastructure mode, mobile units communicate through an

access point that serves as a bridge to other networks (such as Internet or LAN)

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• Infrastructure

infrastructure mode.

a wireless access point hub, and nodes

communicate through the hub

provide service to their client nodes within

range.

phones etc connect to the access point to

join the network.

access points, with the same “SSID –

Service Set Identifier” and security

arrangement

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Types of WLANs

remote base station.

• A main base station is typically connected to the

(wired) Ethernet.

• A relay base station relays data between remote

base stations, wireless clients, or other relay stations; to either a main, or another relay base station.

• A remote base station accepts connections from

wireless clients and passes them on to relay stations or to main stations Connections between

"clients" are made using MAC addresses.

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ENHANCEMENT FOR IEEE

802.11

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Access Methods

• The delivery of MAC Service Data Units (MSDUs) in IEEE 802.11 is asynchronous and performed on a

connectionless basis.

• MSDUs transmitted with best-effort fashion by default

• MAC layer access uses one of following methods:

– Distributed Coordination Function (DCF)

– Point Coordination Function (PCF)

– Hybrid Coordination Function (HCF)

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Access Methods

• DCF

– Based on CSMA/CA

– Senses the medium before sending a frame

– A gap of a minimum specified duration must exist between contiguous frame sequences

– If the medium is busy, the station defers until the end of the current transmission.

– A random backoff interval is used for the determination of the defer period

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– As the infrastructure controls the transmission,

contention can be reduced to some extent

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Access Methods

• HCF

– Combines functions from DCF and PCF with enhancement

on QoS

– Used for QoS network configuration.

– QoS-specific mechanisms allow a uniform set of frame

exchange sequences to be used for QoS data transfer.

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– Introduce traffic categories (TCs) and

provide different priorities to different TCs– Support up to eight queues for different priorities

– Two priority schemes

• Interframe Space (IFS) priority

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Access Methods

• An Arbitration Interframe Space (AIFS) is used

(Arbitration-trọng tài)

• A station can send a data packet or start to decrease its backoff counter after it detects the channel being idle for an AIFS.

• The AIFS is at least as large as the DIFS and can

be adjusted for each TC according to the corresponding priority.

• Thus, the stations with shorter AIFS have a

higher priority to access the channel than the

stations with longer AIFS.

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• Differentiates services by using a different CWmin

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Issues in MAC Protocols

• Support of multicast (send data across a

computer network to several users at the same time)

update membership information

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ETSI HiperLAN (High-Performance

LAN)

asynchronous data effectively at high

can be used for networks with or without

centralized control (base station-mobile

station and ad hoc)

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ETSI HiperLAN

Kbps with a max latency of 10 msec

with 100 msec latency and data rate of

13.4 Mbps

computing for multimedia systems

standard MAC service interface

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ETSI HiperLAN - GOALS

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HiperLAN types 1 and 2 are as follows:

provisions, whereas type 2 has a centralized scheduled MAC.

keying (GMSK), whereas type 2 is based on OFDM

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Features of HiperLAN/2

support for QoS easy

eliminating the need for manual frequency planning as in cellular networks

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A simple HiperLAN system

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HiperLAN/2 Operations

and enter a low power state for a sleep

period.

period, the MS searches for any wake

up signal.

MS goes back to its low-power state for another sleep period

• The control is centralized at the AP

(access point)

Repeat Request) is an error control

mechanism used to increase reliability

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HiperLAN/2 : Radio Link Control

Protocol

• Association control with feature

negotiation Encryption algorithms and

convergence layers, authentication, key

negotiation, and convergence layer

negotiation

• Radio resource control to support

handoff capability, to perform radio

measurements in assisting the APs in

selecting an appropriate radio channel,

and to run the power-saving algorithm

• Connection control for the establishment

and release of user connections

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home), Hiper LAN (for business

workspace)

high speed internet access port

providing data to multiple networked

nodes

a home to simultaneously utilize the same high speed ISP (Internet Servive Provider) account

wired solution and wireless solution.

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• Wired solution:

the cost of wiring and installation is high.

either infrared (IR) or radio frequency

flexibility; is simple, economical, and secure; and is based on industry standards

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HomeRF Technology

same connections for voice and data

of interoperable consumer devices

• A specification for wireless

communications in the home called

Shared Wireless Access Protocol (SWAP) has been developed

Science

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Home RF Network

which are gateways to different resources like cordless phones, printers, fileservers and TV

them in to a single network suitable for all applications and also remove all wires and utilize RF links in the network

• This will support the mobility of devices

connect to PSTN (Public Switched

Telephone Network) ordinarily, but can

also connect through a PC for enhanced services

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Wireless Metropolitan Area

Networks (WMANs)

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IEEE 802.16 based WiMAX

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MAC Layer

point-to-multipoint broadband wireless

access

• It allows very high bit rates in the range of

3.5–0 MHz

terminals per channel that may potentially

be shared by multiple end-users

 The IEEE 802.16 MAC must therefore be

able to accommodate both continuous and

bursty traffic

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MAC Layer Details

allocating bandwidth and transporting

data, the MAC includes a privacy sublayer

access 

data privacy

common part sublayer

– Service-Specific Convergence Sublayers

– Common Part Sublayer

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Sublayers: including

– The ATM convergence sublayer: is defined

for ATM (Asynchronous Transfer Mode)

services, and

– The packet convergence sublayer: is

defined for mapping packet services such

as IPv4, IPv6, Ethernet, and virtual local area network (VLAN)

• Classify service data units (SDUs) to the proper MAC connection, preserve QoS, and enable

bandwidth allocation

on the type of service

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a point-to-multipoint architecture

• On the downlink (DL) (forward channel), data to

the subscriber stations (SSs—essentially the

MSs) are multiplexed in TDM fashion

• The uplink (UL) (reverse channel) is shared between SSs in TDMA fashion.

other purposes

• One connection is reserved for contention-based

initial access

• Another is reserved for broadcast transmissions

in the forward channel as well as for signaling

broadcast contention based polling of SS

bandwidth needs

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MAC PDU Formats

• The MAC PDU (protocol data unit) is the data unit

exchanged between the MAC layers of the BS and its SSs

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MAC PDU Formats

CID: Connection Identifier HCS: Header Check Sequence

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Name Length(bit s) Description

For a MAC header without payload, this bit indicates whether it is Type I or II

the message payload (see below)

and follows the generic MAC header immediately (applic(‘able in both the downlink and uplink)

is included

and initialization vector used to encrypt the payload Evidently, this field is only meaningful if the EC field is set to one

and the CRC, if present

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Wireless Personal Area

Networks (WPANs)

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be commercially available to replace

RS232 cables

802.15.1 (medium rate), and the IEEE

802.15.3 (high rate) and 802.15.4 (low rate) are also available

interworking of wireless technologies to

create heterogeneous wireless

networks

technologies enable users to select the best connectivity

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IEEE 802.15.1 (Bluetooth)

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unified different factions in Christianity

through the country

link eliminates the need for short cable

• Bluetooth radio technology built into both the cellphone and the laptop would

replace the cable used today to connect a laptop to cellphone

• Printers, desktops can all be wireless

• It also provides a universal bridge to

existing data networks

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products (PC/Laptops) have only one wire attached to power cord

eliminated

• A simple application of Bluetooth is

updating the phone directory of the PC

from a mobile telephone

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overhead for links.

application range

Modulation) voice coding that can

withstand high bit error rates

to minimize power consumption

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Architecture of Bluetooth

System

uses shorter packets as compared to

other systems operating in the same

frequency band

limits the impact of random noise

performance decreases

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System

3 bit Active Member address.

synchronized to the Master through

remaining inactive slaves, referred to as

parked nodes.

the master clock and can become active and start communicating in the Piconet

anytime

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System

• If Piconets are close to each other, they have overlapping areas

more Piconets mingle is called

Scatternet.

created all devices are in STDBY mode.

periodically “listens” for message every

1.28 seconds

the set of 32 hop frequencies defined for that unit

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Bluetooth Core Protocol

LMP – Link Manager Protocol

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Bluetooth Core Protocol

• SDP: Provides a mean for applications to

discover which services are provided by or available through a Bluetooth device

• L2CAP: Supports higher level protocol

multiplexing, packet segmentation and

reassembly and conveying of QoS

information

• LMP: Used by Link managers for link set

up and control

• Baseband: Enables the physical RF link

between Bluetooth units forming a

Piconet

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IEEE 802.15.3

an ad hoc MAC layer suitable for

multimedia WPAN applications and a

PHY capable of data rates in excess of 20 Mbps

standard (being dubbed WiMedia)

specifies data rates of up to 55 Mbps in

the 2.4 GHz unlicensed band

either Bluetooth or the IEEE 802.11 family

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IEEE 802.15.3 MAC Layer

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IEEE 802.15.3 PHY Layer

Specification

band between 2.4 GHz and 2.4835 GHz

same symbol rate, 11 Mbaud, as used in the IEEE 802.11b systems

specified—namely, uncoded QPSK at 22 Mbs and trelliscoded QPSK, 16/32/64-

QAM at 11, 33, 44, 55Mbs

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mA) while actively transmitting or receiving data

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IEEE 802.15.4

IEEE 802WG came together to specify the

interfaces and the working of the LR–PAN

the MAC and the PHY layers

maintaining higher layers above the MAC.

done mostly by Philips and Motorola for

ZigBee

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IEEE 802.15.4

peer-topeer topology

bit) and network assigned (8 bit)—are

allowed

selforganizing and self-maintaining to

minimize cost to the customer

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IEEE 802.15.4 Data Link Layer

(DLL)

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(DLL)

services to an IEEE 802.2 type 1 LLC

through the service specific

convergence sublayer (SSCS).

layer directly without going through the

SSCS

• The SSCS ensures compatibility between

different LLC sublayers and allows the

MAC to be accessed through a single set

of access points

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(DLL)

– MAC data service, through the MAC

common part sublayer (MCPS–SAP)

– MAC management services, through the

MAC layer management entity (MLME–SAP)

SSCS (or another LLC) and the PHY layer

primitives as compared to the IEEE 802.15.1, which has 131 primitives and 32 events.

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– 2.4 GHz ISM band, available worldwide

– 868/915 MHz for Europe and the US, respectively

• Data rates supported

kbps

sensitivity and larger coverage area The

higher rate means lower duty cycle, higher

throughput, and lower latencies

• Range: typical devices (1 mW) are expected

to cover a range of 10–20m

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