第五章小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage

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现代通信新技术导论

第五章小覆盖无线网络Chapter 5 Wireless Networks with Narrow Coverage

电控学院电子工程学科部司鹏搏综合楼 825 室[email protected]

现代通信新技术导论第五章小覆盖无线网络

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Main Contents• 5.1 Wireless Local Area Networks (WLANs)

– 5.1.1 Wireless Networks– 5.1.2 IEEE 802.11 Overview– 5.1.3 Components– 5.1.4 Services– 5.1.5 MAC Layer– 5.1.6 Physical Layer– 5.1.7 IEEE 802.11 Protocols

• 5.2 Wireless Personal Area Networks (WPANs)• 5.3 Wireless Body Area Networks (WBANs)


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Main Contents• 5.1 Wireless Local Area Networks (WLANs)• 5.2 Wireless Personal Area Networks (WPANs)

– 5.2.1 Introduction to Bluetooth– 5.2.2 Protocol Stack– 5.2.3 Network Topology– 5.2.4 Packet Structure– 5.2.5 Connection States– 5.2.6 Security– 5.2.7 Technology Comparison and Target Markets

• 5.3 Wireless Body Area Networks (WBANs)


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Main Contents• 5.1 Wireless Local Area Networks (WLANs)• 5.2 Wireless Personal Area Networks (WPANs)• 5.3 Wireless Body Area Networks (WBANs)

– 5.3.1 Introduction to WBAN– 5.3.2 Three-Tier Architecture – 5.3.3 Comparison with Other Networks– 5.3.4 Designing WBANs– 5.3.5 Physical Layer Considerations– 5.3.6 MAC Layer Considerations– 5.3.7 Network Layer Considerations


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5.1.1 Wireless Internetworking Overview

Fixed Mobile

Broadband Multiservice2G+

Cellular3G

Cellular

Residential/Premise/ Campus

LMDSMMDS DataServices

GPRSMobile IP

PacketData/Voice

UMTS

BLUETOOTH

IEEE802.11


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5.1.1 Standardization of Wireless Networks• Wireless networks are standardized by IEEE.• Under 802 LAN MAN standards committee.

Application

Presentation

Session

Transport

Network

Data Link

Physical

ISOOSI7-layermodel

Logical Link Control

Medium Access (MAC)

Physical (PHY)

IEEE 802standards


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5.1.2 IEEE 802.11 Overview• Goals

– To deliver services in wired networks– To achieve high throughput– To achieve highly reliable data delivery– To achieve continuous network connection

• Adopted in 1997.• Defines

– MAC sublayer – MAC management protocols and services– Physical (PHY) layers

• IR • FHSS• DSSS


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5.1.3 Components• Station• BSS - Basic Service Set

– IBSS : Independent BSS• ESS - Extended Service Set

– A set of infrastructure BSSs– Connection of APs– Tracking of mobility

• DS – Distribution System– AP communicates with another


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5.1.3 BSS• A set of stations controlled by a single “Coordination

Function” – = the logical function that determines when a station can transmit

or receive• Similar to a “cell” in pre IEEE terminology• A BSS can

– Have an Access-Point (both in standalone networks and in building-wide configurations),

– Or can run without and Access-Point (in standalone networks only)• Diameter of the cell is approximately twice the coverage-

distance between two wireless stations


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5.1.3 BSS

BSS


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5.1.3 IBSS• A Basic Service Set (BSS) which forms a self-

contained network in which no access to a Distribution System is available

• A BSS without an Access-Point• One of the stations in the IBSS can be configured

to “initiate” the network and assume the Coordination Function

• Diameter of the cell determined by coverage distance between two wireless stations


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5.1.3 IBSS

IBSS


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5.1.3 ESS and DS• Extended Service Set (ESS):

– A set of one or more Basic Service Sets interconnected by a Distribution System (DS)

– Traffic always flows via Access-Point– Diameter of the cell is double the coverage distance between two

wireless stations• Distribution System (DS):

– A system to interconnect a set of Basic Service Sets• Integrated; A single Access-Point in a standalone network• Wired; Using cable to interconnect the Access-Points• Wireless; Using wireless to interconnect the Access-Points


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5.1.3 ESS, Single BSS with Integrated DS

BSS


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5.1.3 ESS, BSSs with Wired DS

BSS

BSS

Distribution System


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5.1.3 ESS, BSSs with Wireless DS

BSS

BSS

Distribution

System


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5.1.3 SSID and BSSID• Service Set Identifier (SSID):

– “Network name” – 32 octets long– Similar to “Domain-ID” in the pre-IEEE WaveLAN systems– One network (ESS or IBSS) has one SSID

• Basic Service Set Identifier (BSSID)– “cell identifier”– 6 octets long (MAC address format)– Similar to NWID in pre-IEEE WaveLAN systems– One BSS has one SSID – Value of BSSID is the same as the MAC address of the radio in the Access-

Point


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5.1.4 Services• Station services:

– Authentication– De-authentication– Privacy– Delivery of data

• Distribution Services (A thin layer between MAC and LLC)– Association– Disassociation– Reassociation– Distribution– Integration


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5.1.5 Medium Access Control• Functionality

– Reliable data delivery– Fairly control access – Protection of data

• Deals– Noisy and unreliable medium– Frame exchange protocol - ACK– Overhead to IEEE 802.3 – Hidden Node Problem – RTS/CTS– Participation of all stations– Reaction to every frame


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5.1.5 Medium Access Control• Retry Counters

– Short retry counter– Long retry counter– Lifetime timer

• Basic Access Mechanism– CSMA/CA– Binary exponential back-off– NAV – Network Allocation Vector

• Timing Intervals: SIFS, Slot Time, PIFS, DIFS, EIFS• DCF Operation• PCF Operation


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5.1.5 Hidden Node Problem

• A and C cannot see each other, B can see both

A B C


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5.1.5 CSMA/CA• Sender sends Request to Send (RTS)• Receiver sends Clear to Send (CTS)• Sender transmits for required time

RTS

CTS


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5.1.5 DCF Operation


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5.1.5 PCF Operation• Poll – eliminates contention• PC – Point Coordinator

– Polling List– Over DCF– PIFS

• CFP – Contention Free Period– Alternate with DCF

• Periodic Beacon – contains length of CFP• CF-Poll – Contention Free Poll• NAV prevents during CFP• CF-End – resets NAV


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5.1.5 Frame Types

• Protocol Version• Frame Type and Sub

Type• To DS and From DS• More Fragments • Retry • Power Management • More Data • WEP• Order

FC Duration/ID

Address 1

Address 2

Address 3

SequenceControl

Address4 DATA FCS

2 2 6 6 6 2 6 0-2312 4 bytes

NAV informationOr Short Id for PS-Poll

BSSID –BSS Identifier

TA - Transmitter RA - Receiver SA - Source DA - Destination

IEEE 48 bit address

Individual/Group Universal/Local 46 bit address

MSDU Sequence

Number Fragment

Number

CCIT CRC-32 Polynomial

Upper layer data 2048 byte max 256 upper layer

header


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5.1.5 Frame Control Field

MAC Header format differs per Type:– Control Frames (several fields are omitted)– Management Frames– Data Frames

FrameControl

DurationID Addr 1 Addr 2 Addr 3 Addr 4Sequence

Control CRCFrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:

ProtocolVersion Type SubType To

DS Retry PwrMgt

MoreData WEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DSFrom More

Frag


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5.1.5 Address Field

Addr. 1 = All stations filter on this address.Addr. 2 = Transmitter Address (TA), Identifies transmitter to address the ACK frame to.Addr. 3 = Dependent on To and From DS bits.Addr. 4 = Only needed to identify the original source of WDS (Wireless Distribution System)

frames


DS Retry PwrMgt

MoreData WEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DSFrom More

Frag

To DS0011

From DS0101

Address 1DADA

BSSIDRA

Address 2SA

BSSIDSATA

Address 3BSSID

SADADA

Address 4N/AN/AN/ASA


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5.1.5 Type Field

Type and subtype identify the function of the frame:Type=00 Management Frame

Beacon (Re)AssociationProbe (De)Authentication

Power Management

Type=01 Control FrameRTS/CTS ACK

Type=10 Data Frame


DS Retry PwrMgt

MoreData WEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DSFrom More

Frag


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5.1.5 MAC Management Frames• Beacon

– Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters

– Traffic Indication Map• Probe

– SSID, Capabilities, Supported Rates• Probe Response

– Timestamp, Beacon Interval, Capabilities, SSID, Supported Rates, parameters

– Same as Beacon except for TIM• Association Request

– Capability, Listen Interval, SSID, Supported Rates


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5.1.5 MAC Management Frames• Association Response

– Capability, Status Code, Station ID, Supported Rates• Re-association Request

– Capability, Listen Interval, SSID, Supported Rates, Current AP Address• Re-association Response

– Capability, Status Code, Station ID, Supported Rates• Dis-association

– Reason code• Authentication

– Algorithm, Sequence, Status, Challenge Text• De-authentication

– Reason


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5.1.5 Frame Subtypes

• RTS• CTS• ACK• PS-Poll• CF-End & CF-End

ACK

Data Data+CF-ACK Data+CF-Poll Data+CF-ACK+CF-

Poll Null Function CF-ACK (nodata) CF-Poll (nodata) CF-ACK+CF+Poll

Beacon Probe Request & Response Authentication Deauthentication Association Request &

Response Reassociation Request &

Response Disassociation Announcement Traffic

Indication Message (ATIM)

CONTROL DATA MANAGEMENT


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5.1.5 Other MAC Operations• Fragmentation

– Sequence control field– In burst– Medium is reserved– NAV is updated by ACK

Privacy WEP bit set when encrypted. Only the frame body. Medium is reserved NAV is updated by ACK Symmetric variable key

WEP Details Two mechanism

Default keys Key mapping

WEP header and trailer KEYID in header ICV in trailer

dot11UndecryptableCount Indicates an attack.

dot11ICVErrorCount Attack to determine a

key is in progress.


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5.1.5 MAC Management and Authentication• MAC Management

– Interference by users that have no concept of data communication. Ex: Microwave– Interference by other WLANs– Security of data– Mobility– Power Management

• Authentication– Prove identity to another station.– Open system authentication– Shared key authentication

• A sends• B responds with a text• A encrypt and send back• B decrypts and returns an authentication management frame.

– May authenticate any number of station

• Security Problem– A rogue AP

• SSID of ESS• Announce its presence with

beaconing• An active rogue AP reaches higher

layer data if unencrypted


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5.1.5 Association• Transparent mobility• After authentication• Association request to an AP• After established, forward data

– To BSS, if DA is in the BSS.– To DS, if DA is outside the BSS.– To AP, if DA is in another BSS.– To “portal”, if DC is out of the ESS.

• New AP after reassociation, communicates with the old AP.


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5.1.5 Power Management• Independent BSS

– Distributed– Data frame handshake– Wake up every beacon.– Awake a period of ATIM after each

beacon.– Send ACK if receive ATIM frame &

awake until the end of next ATIM.– Estimate the power saving station,

and delay until the next ATIM.– Multicast frame : No ACK :

optional

• Overhead– Sender

• Announcement frame• Buffer • Power consumption in

ATIM– Receiver

• Awake for every Beacon and ATIM


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5.1.5 Power Management• Infrastructure BSS

– Centralized in the AP– Greater power saving– Mobile Station sleeps for a number of beacon

periods.– Awake for multicast indicated in DTIM in Beacon.– AP buffer, indicate in TIM– Mobile requests by PS-Poll


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5.1.5 Synchronization• Timer Synchronization in an Infrastructure BSS

– Beacon contains TSF– Station updates its with the TSF in beacon.

• Timer Synchronization in an IBSS– Distributed. Starter of the BSS send TSF zero and

increments.– Each Station sends a Beacon– Station updates if the TSF is smaller– Take into account the contention time


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5.1.5 Scanning & Joining• Scanning

– Passive Scanning : only listens for Beacon and get info of the BSS. Power is saved

– Active Scanning: transmit and elicit response from APs. If IBSS, last station that transmitted beacon responds. Time is saved

• Joining a BSS– Synchronization in TSF and frequency : Adopt PHY

parameters : The BSSID : WEP : Beacon Period : DTIM


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5.1.5 Operational Process• Association

– To establish relationship with Access-Point– Stations scan frequency band to and select Access-Point with best

communications quality• Active Scan (sending a “Probe request” on specific channels and assess

response)• Passive Scan (assessing communications quality from beacon message)

– Access-Point maintains list of associate stations• Record station capability (data-rate)• To allow inter-BSS relay

– Station’s MAC address is also maintained in bridge learn table associated with the port it is located on


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5.1.5 Operational Process• Authentication

– To control access to the infrastructure via an authentication– Stations identify themselves to other stations (or Access-

Points) prior to data traffic or association– Open System Authentication

• Uses null authentication algorithm• Default

– Shared Key Authentication • Uses WEP privacy algorithm• Optional


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5.1.5 Operational Process• Starting an ESS

– The infrastructure network is identified by its ESSID – All Access-Points will have been set according to this

ESSID– Wireless stations will be configured to set their desired

SSID to the value of ESSID– On power up stations will issue Probe Requests and will

locate the Access-Point that they will associate with:• “Best” Access-Point with matching ESSID • “Best” Access-Point if the “desired SSID” has been set to “ANY”


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5.1.5 Operational Process• Starting an IBSS

– Station configured for IBSS operation will:• “look” for Beacons that contain a network name (SSID) that matches the one

that is configured • When Beacons with matching Network Name are received and are issued by an

AP, Station will associate to the AP• When Beacons with matching Network Name are received and are issued by

another Station in IBSS mode, the station will join this IBSS• When no beacons are received with matching Network Name, Station will issue

beacons itself.– All Stations in an IBSS network will participate in sending beacons.

• All stations start a random timer prior to the point in time when next Beacon is to be sent.

• First station whose random timer expires will send the next beacon


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5.1.5 Operational Process

• Inter-Frame Spacing– Inter frame spacing required for MAC protocol traffic

• SIFS = Short interframe space• PIFS = PCF interframe space• DIFS = DCF interframe space

– Back-off timer expressed in terms of number of time slots

DIFS Contention Window

Slot time

Defer Access

Backoff-Window Next Frame

Select Slot and Decrement Backoff as long as medium is idle.

SIFS

PIFSDIFS

Free access when mediumis free longer than DIFS

Busy Medium


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• Data Frames and their ACK– Acknowledgment are to arrive at within the SIFS– The DCF interframe space is observed before medium is considered

free for use

ACK

Data

Next MPDU

Src

Dest

Other

Contention Window

Defer Access Backoff after Defer

DIFS

SIFS

DIFS


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5.1.5 Operational ProcessAP-1000 or AP-500

Wireless PC-Card

Association table

Inter-BSS Relay

Bridge learn table

STA-1

BSS-A

Associate

STA-2

AssociatePacket for STA-2ACK Packet for STA-2

ACK

STA-1

STA-1

2

STA-2

STA-2 2

• Traffic Flow——Inter BSS


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STA-1 STA-2BSS-A

BSS-B

Backbone

Packet for STA-2

ACK

Packet for STA-2ACK

AP-1000 or AP-500

Avaya Wireless PC-Card

Association table

Bridge learn table

AP-1000 or AP-500


Association table

Bridge learn table

STA-1

STA-2 1

STA-1

STA-2

STA-1

2 STA-2

2

1

• Traffic Flow ——ESS Operation


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STA-1 STA-2BSS-A

BSS-B

Packet for STA-2

ACK

Packet for STA-2ACK

AP-1000 or AP-500


Association table

Bridge learn table

AP-1000 or AP-500


Association table

Bridge learn table

STA-1

STA-2 2

STA-1

STA-2

STA-1

2 STA-2

2

2

Wireless

Backbone

WDS Relay

WDS RelayPacket for STA-2

ACK

• Traffic Flow ——WDS Operation


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5.1.6 Physical Layer• Direct Sequence Spread Spectrum (DSSS) PHY

– 2.4 GHz : RF : 1 – 2 Mbps• The Frequency Hopping Spread Spectrum (FHSS) PHY

– 110KHz deviation : RF : PMD controls channel hopping : 2 Mbps• Infrared (IR) PHY

– Indoor : IR : 1 and 2 Mbps• The OFDM PHY – IEEE 802.11a

– 5.0 GHz : 6-54 Mbps • High Rate DSSS PHY – IEEE 802.11b

– 2.4 GHz : 5.5 Mbps – 11 Mbps


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5.1.6 FHSS and DSSS in Physical Layer• Preamble Sync, 16-bit Start Frame Delimiter, PLCP Header including 16-

bit Header CRC, MPDU, 32-bit CRC• FHSS

– 2 & 4GFSK– Data Whitening for Bias Suppression

• 32/33 bit stuffing and block inversion• 7-bit LFSR scrambler

– 80-bit Preamble Sync pattern– 32-bit Header

• DSSS– DBPSK & DQPSK– Data Scrambling using 8-bit LFSR– 128-bit Preamble Sync pattern– 48-bit Header


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5.1.6 Other Issues in Physical Layer• Antenna Diversity

– Multipath fading a signal can inhibit reception– Multiple antennas can significantly minimize– Spatial Separation of Orthoganality– Choose Antenna during Preamble Sync pattern

• Presence of Preamble Sync pattern• Presence of energy

– RSSI - Received Signal Strength Indication• Combination of both

• Clear Channel Assessment– Require reliable indication that channel is in use to defer transmission– Use same mechanisms as for Antenna Diversity– Use NAV information


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5.1.7 IEEE 802.11 Protocols• IEEE 802.11a

– 1999 : PHY Standard : 8 channels : 5 GHz : 54 Mbps • IEEE 802.11b

– 1999 : PHY Standard : 3 channels : 2.4 GHz : 11 Mbps • IEEE 802.11d

– MAC Standard : operate in variable power levels : ongoing

• IEEE 802.11e– 2002 : MAC Standard : QoS support


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5.1.7 IEEE 802.11 Protocols• IEEE 802.11f

– Inter-Access Point Protocol : 2nd half 2002• IEEE 802.11g

– 2000 : PHY Standard: 3 channels : OFDM and PBCC : 54 Mbps• IEEE 802.11h

– 2002 : Supplementary MAC Standard: TPC and DFS • IEEE 802.11i

– 2004 : Supplementary MAC Standard: Alternative WEP • IEEE 802.11n

– 2009 : MIMO OFDM : 600 Mbps? 100 Mbps?


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5.1.7 IEEE 802.11e• EDCF - Enhanced DCF• HCF - Hybrid Coordination Function• QBSS• HC – Hybrid Controller• TC – Traffic Categories• TXOP – Transmission Opportunity

– Granted by EDCF-TXOP or HC- poll TXOP• AIFS – Arbitration Interframe Space


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5.1.7 Operational Process of 802.11e


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5.1.7 IEEE 802.11e Backoff


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5.1.7 IEEE 802.11iDescription Enhancements to the 802.11 MAC standard to increase the security; addresses

new encryption methods and upper layer authentication

Importance High: weakness of WEP encryption is damaging the 802.11 standard perception in the market

Related standards This applies to 802.11b, 802.11a and 802.11g systems.802.1x is key reference for upper layer authentication

Status +Roadmap

Enhanced encryption software will replace WEP software; This is on a recommended best practice /voluntary basis; development in TgI: first draft Mar 2001; next draft due Mar 2002; stable draft: July 2002; final standard: Jan 2003

Products affected Client and AP cards (Controller chip, Firmware, Driver)AP kernel, RG kernel, BG kernel

Agere’s activity Actively proposing WEP improvement methods, participating in all official/interim meetings

Key players Agere/Microsoft/Agere/Cisco/Atheros/Intel/3Com/Intersil/Symbol/Certicom/RSA/Funk

Key issues Mode of AES to use for encryption (CTR/CBC [CBC MIC] or OCB [MIC and Encryption function])


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5.2.1 What is Bluetooth?• Bluetooth is a short-range wireless network originally

intended to replace the cable(s) connecting portable and/or fixed electronic devices. Such a network is also sometimes called a PAN (Personal Area Network)

• Bluetooth is supposed to got it’s name from Harald “Bluetooth” II, King of Denmark 940-981

• The concept was first patented by Ericsson. Currently the Bluetooth trade mark is owned by the Bluetooth SIG, a consortium of companies having stake in Bluetooth

• Key features are robustness, low power, and low cost.


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5.2.1 What can Bluetooth Do?

Personal Ad Hoc Networks

Cable Replacement

Landline

Data/Voice Access Points

现代通信新技术导论第五章小覆盖无线网络5.2.1 What can Bluetooth Do?

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现代通信新技术导论第五章小覆盖无线网络5.2.1 What can Bluetooth Do?

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5.2.1 What can Bluetooth Do?

In the Office

At Home


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5.2.1 Bluetooth Overview

Connection Type Spread Spectrum (Frequency Hopping)

MAC Scheme FH-CDMA

Spectrum 2.4 GHz ISM

Modulation Gaussian Frequency Shift Keying

Transmission Power 1 mw – 100 mw

Aggregate Data Rate 1 Mbps

Range 30 ft (~9 m)

Supported Stations 8 devices

Voice Channels 3

Data Security- Authentication Key 128 bit key

Data Security-Encryption Key 8-128 bits (configurable)


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5.2.2 Protocol Stack——Transport Protocol Group

Composed of protocols to allow Bluetooth devices to locate each other and to create, configure and manage both physical and logical links that allow higher layer protocols and applications to pass data through these transport protocols

RFBaseband

AudioLink ManagerL2CAP

Data

SDP RFCOMMIP

Cont

rol

Applications

Transport Protocol Group


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5.2.2 Transport Protocol Group• Radio Frequency (RF)

– Sending and receiving modulated bit streams• Baseband

– Defines the timing, framing– Flow control on the link.

• Link Manager – Managing the connection states.– Enforcing Fairness among slaves.– Power Management

• Logical Link Control &Adaptation Protocol– Handles multiplexing of higher level protocols– Segmentation & reassembly of large packets– Device discovery & QoS

现代通信新技术导论第五章小覆盖无线网络5.2.2 Protocol Stack——Middleware Protocol Group

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Middleware Protocol Group

RFBaseband


Data

SDP RFCOMMIP

Con

trol

Applications

Middleware Protocol Group

Additional transport protocols to allow existing and new applications to operate over Bluetooth. Packet based telephony control signaling protocol also present. Also includes Service Discovery Protocol.


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5.2.2 Middleware Protocol Group• Service Discovery Protocol (SDP)

– Means for applications to discover device info, services and its characteristics.

• TCP/IP– Network Protocols for packet data communication,

routing• RFCOMM

– Cable replacement protocol, emulation of serial ports over wireless network


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5.2.2 Protocol Stack——Application Group

Application Group

RFBaseband


Data

SDP RFCOMMIP

Con

trol

Applications

Consists of Bluetooth aware as well as un-aware applications.


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5.2.3 Network Topology• Master

– Device in Piconet whose clock and hopping sequence are used to synchronize all other devices (slaves) in the Piconet.

– It also carries out Paging procedure and also Connection Establishment.

MM

S

S S

S

P

sb

sb

P

P

• Slaves– Units within the piconet that are

synchronized to the master via its clock and hopping sequence.

– After connection establishment, Slaves are assigned a temporary 3 bit member address to reduce the no. of addressing bits required


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5.2.3 Network Topology• Point to Point Link

– Master - slave relationship– Bluetooth devices can function as masters or slaves

• Piconet– It is the network formed by a Master and one or

more slaves (max 7).– Each piconet is defined by a different hopping

channel to which users synchronize to.– Each piconet has max capacity (1 Mbps).– Hopping pattern is determined by the master.

m s

s s s

m


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5.2.3 Physical Link Types• Synchronous Connection Oriented (SCO)

– Point to Point Full Duplex between Master & Slave– Established once by master & kept alive till released by Master– Typically used for Voice connection ( to guarantee continuity )– Master reserves slots used for SCO link on the channel to preserve

time sensitive information • Asynchronous Connection Link (ACL)

– It is a momentary link between master and slave.– No slots are reserved.– It is a Point to Multipoint connection.– Symmetric & Asymmetric links possible


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5.2.4 Packet Structure72 bits 54 bits 0 - 2744 bits

DataVoice CRC

No CRCNo retries

header

ARQ

FEC (optional) FEC (optional)

Access Code

Header Payload


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5.2.4 Access Code• Purpose

– Synchronization – DC offset compensation – Identification – Signaling

• Types– Channel Access Code (CAC)

• Identifies a piconet.– Device Access Code (DAC)

• Used for signalling procedures like paging and response paging.– Inquiry Access Code (IAC)

• General IAC is common to all devices, Dedicated IAC is for a dedicated group of Bluetooth devices that share a common characteristic.


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5.2.4 Packet Header

• AM_ADDR: 3 bits: address of slave in piconet.• TYPE: One of 16 possible packet types• FLOW: Used to stop flow on ACL link. • ARQN: Positive or negative acknowlegement.• SEQN: Inverted for each new transmitted packet. • HEC: Header-error check. • The entire header is protected by 1/3 rate FEC.


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5.2.5 Connection State Machine

Standby

Inquiry Page

Connected

Transmit data

Park Hold Sniff


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5.2.5 Connection State Machine• Inquiry Scan

– A device that wants to be discovered will periodically enter this mode and listen for inquiry packets.

• Inquiry– Device sends an Inquiry packet addressed to GIAC or DIAC– Transmission is repeated on the inquiry hop sequence of

frequencies.• Inquiry Response

– When an inquiry message is received in the inquiry scan state, a response packet (FHS) containing the responding device address must be sent after a random number of slots.


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5.2.5 Connection State Machine• Page

– The master uses the clock information, about the slave to be paged, to determine where in the hop sequence, the slave might be listening in the page scan mode.

– The master sends a page message• Page Scan

– The page scan substate can be entered by the slave from the standby state or the connection state. It listens to packets addressed to its DAC.

• Page Response– On receiving the page message, the slave enters the slave page response

substate. It sends back a page response consisting of its ID packet which contains its DAC, at the frequency for the next slot from the one in which page message was received.


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5.2.5 Power Control Modes• Sniff Mode

– This is a low power mode in which the listening activity of the slave is reduced.

– In the sniff mode, the slave listens for transmissions only at fixed intervals Tsniff, at the offset slot Dsniff for Nsniff times. These parameters are given by the LMP in the master when it issues the SNIFF command to the slave.

• Hold Mode– Slave temporarily (for Thold sec) does not support ACL packets on the

channel (possible SCO links will still be supported). – By this capacity can be made free to do other things like scanning, paging,

inquiring, or attending another piconet. – The slave unit keeps its active member address (AM_ADDR).


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5.2.5 Power Control Modes• Park Mode

– This is a very low power mode with very little activity.– The slave however, stays synchronized to the channel. – The parked slaves regularly listen for beacon signals at intervals

decided by the beacon structure communicated to the slave during the start of parking.

– The parked slave has to be informed about a transmission in a beacon channel which is supported by the master to keep parked slaves in synchronization and send them any other information.

– Any message to be sent to a parked member are sent over the broadcast channel.

– It also helps the master to have more than seven slaves.


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5.2.6 Security• Security Measures

– Limited/Restricted Access to authorized users.– Both Link Level Encryption & Authentication.– Personal Identification Numbers (PIN) for device access.– Long encryption keys are used (128 bit keys).– These keys are not transmitted over wireless. Other parameters are transmitted

over wireless which in combination with certain information known to the device, can generate the keys.

– Further encryption can be done at the application layer.• Security values

– Device Address-Public– Authentication Key(128 bits)-Private– Encryption Key(8-128 bits)-Private– Random Number


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5.2.7 Bluetooth v.s. IrDA• Bluetooth Advantages

– Point to Multipoint– Data & Voice– Broadcast– Easier Synchronization due to omnidirectional and no LOS requirement– Devices can be mobile– Range 10 m

• IrDA– Point to point– Intended for Data Communication– Currently 16 Mbps– Ample security and very less interference– Already ubiquitous & Low cost– Infrared, LOS, serial data comm.– Simple to configure and use– Both devices must be stationary, for synchronization


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5.2.7 Bluetooth Target Markets• The first wave

– PC, Notebooks– Organizers & Palm Computers– Headsets – Cellular/ PCS – Cordless phones – Automotive cellular– Digital cameras

• The second wave– Printers– Photo printers– Fax machines– Industrial, musical and vertical industries

products


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5.3.1 What is WBAN• Wireless Body Area Network

– Consists of a set of mobile and compact intercommunicating sensors, either wearable or implanted into the human body, which monitor vital body parameters and movements

– These devices, communicating through wireless technologies, transmit data from the body to a home base station, from where the data can be forwarded to a hospital, clinic or elsewhere, real-time

– Still in its primitive stage and is being widely researched– Is expected to be a breakthrough invention in healthcare

• IEEE 802.15.6 is the task group for BAN.


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5.3.1 Motivations of WBAN• Goal: ubiquitous and affordable healthcare• Opportunities:

– Ambulatory ( 流动的 ) health monitoring– Computer-assisted rehabilitation ( 康复 )– Augmented reality systems

• Long-term benefits:– Promote healthy lifestyle– Seamless integration of data into personal medical records

and research databases – Knowledge discovery through data mining


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5.3.2 Three-Tier Architecture of WBAN


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5.3.2 Tier 1: WBAN• Consisted of intelligent nodes

– Sensing– Sampling– Processing – Communicating


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5.3.2 Body Sensors

Signal Conditioning RS232 Interface

MicrocontrollerFinger Probe Programmable Logic


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5.3.2 Tier 2: Personal Server• As the interface of WBAN sensor nodes through Zigbee or

Bluetooth.• Connected with the medical server through mobile

telephone networks (2G, GPRS, 3G) or WLANs—Internet• Implemented regularly at cell phone• Functions

– Register type and number sensor node .– Manages the network channel sharing, time synchronization,

and processing data.– Send data to MS


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5.3.2 Tier 3• Function:

– Authenticate the users – Save patient data into medical records – Analyze the data – Recognize serious health cases in order to

contact emergency care givers – Forward new instruction to user


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5.3.3 Comparison with Other Networks


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5.3.3 Comparison with Other Networks

“Self-awareness”• Local environment• Automatic configuration

arrangement of devices, services, and local connectivity

• Automatic and multi-modal interfaces

“Group-awareness”• Context and presence support• Novel privacy and trust models“World-awareness”• Automatic support for seamless

access to and delivery of services across different domains

Communication Spheres

BAN – Body Area Network• Bluetooth, RFID, sensors, …

PAN – Personal Area Network• Bluetooth, WLAN, …

WAN – Wide Area Network• 3G, B3G, WLAN, *DSL, …

People shift between different roles in participating different groups, using multiple devices with different modalities over different networks


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5.3.3 Data Rate v.s. Power Consumption


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5.3.4 Designing WBANs• Types of Devices

– Wireless sensor node• A device that responds to and gathers data on physical stimuli, processes the data

if necessary and reports this information wirelessly. It consists of several components: sensor hardware, a power unit, a processor, memory and a transmitter or transceiver.

– Wireless actuator node• A device that acts according to data received from the sensors or through

interaction with the user. The components of an actuator are similar to the sensor's: actuator hardware, a power unit, a processor, memory and a receiver or transceiver.

– Wireless personal device• A device that gathers all the information acquired by the sensors and actuators

and informs the user via an external gateway, an actuator or a display/LEDS on the device. The components are a power unit, a processor, memory and a transceiver. This device is also called a Body Control Unit, body-gateway or a sink. In some implementations, a PDA or smart phone is used.


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5.3.4 Data Rate Issue• Examples of Medical Applications


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5.3.4 Other Issues• Energy Issue

– Restricted by battery capacity• Sensing• Communication (most power consuming)

– RF radiation• Data processing

• QoS Issue– Data loss rate– Delivery time delay

• Security and Privacy Issue– Data safety– Should be accessible when the user is not capable of giving the pwd


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5.3.4 Positioning WBAN


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5.3.5 Physical Layer Considerations• RF Communications

– Minimize the transmit power– In the body

• Channel losses are mainly due to the absorption in the tissue, very high compared to the free space propagation, related to heat

• Specific absorption rate is defined– Along the body

• LOS• NLOS, multi-hop

• Movement of the Body• Non-RF Communications

– Body-coupled communication– Transfer data by capacitive and galvanic coupling– Low frequency (10 kHz to 10 MHz) and low data rate (5 bps)


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5.3.6 MAC Layer Considerations• Non-Specific MAC protocols designed for WBAN Yet• Requirement

– Simple– Low cost

• Applicable MAC Protocols– CSMA/CA– Bluetooth MAC protocol– 802.15.4

• QoS guarantee, but not scalable in terms of power consumption– 802.15.6

• Designed for WBAN, under standardization


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5.3.7 Network Layer Considerations• Temperature Routing

– Thermal aware routing algorithm– Adaptive least temperature routing– Least total route temperature

• Cluster Based Routing– Protocols based on LEACH


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A Brief Review• WLAN

– Coverage: office, airport, building, …– Wi-Fi, IEEE 802.11– CSMA/CA, DCF/PCF/PSM/…

• WPAN– Coverage: personal devices– Bluetooth– MAC/PHY

• WBAN– Coverage: body sensors– Medical applications

Documents

第五章 小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage

第五章小覆盖无线网络 Chapter 5 Wireless Networks with Narrow Coverage