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Chapter 14무선 LAN
(Wireless LAN)
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14 14 장 무선랜장 무선랜
14.1 IEEE 802.11
14.2 블루투스
14.3 요 약
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14.1 IEEE 802.1114.1 IEEE 802.11
Topics discussed in this section:Topics discussed in this section:
IEEE has defined the specifications for a wireless LAN, IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data called IEEE 802.11, which covers the physical and data link layers.link layers.
ArchitectureArchitectureMAC SublayerMAC Sublayer
Physical LayerPhysical Layer
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IEEE 802.11IEEE 802.11 (( 계속계속 ))
IEEE 802.11
■ 무선 LAN 에 대한 명세
구조
■ 기본 서비스 세트 (BSS, basic service set)
■ 확장 서비스 세트 (ESS, extended service set)
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IEEE 802.11IEEE 802.11 (( 계속계속 ))
5
A BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Basic service sets(BSSs)
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Extended service sets(ESSs)
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) 지국 유형
■ 무전이 이동성 (NO-Transition Mobility)
■ BSS 전이 이동성 (BSS-Transition Mobility)
■ ESS 전이 이동성 (ESS-Transition Mobility)
물리층■ 비트를 신호로 변환에 대한 명세 ( 무선주파수 )
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) MAC layers in IEEE 802.11 standard
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) CSMA/CA flowchart
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) CSMA/CA and NAV
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Example of repetition interval
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Frame format
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Subfields in FC field
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Control frames
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Values of subfields in control frames
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Addresses
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Addressing mechanisms
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Hidden station problem
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IEEE 802.11 (IEEE 802.11 ( 계속계속 ))
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The CTS frame in CSMA/CA handshake can prevent collision from
a hidden station.
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Use of handshaking to prevent hidden station problem
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Exposed station problem
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IEEE 802.11 (IEEE 802.11 ( 계속계속 ))
23
Use of handshaking in exposed station problem
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Physical layers
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Industrial, scientific, and medical (ISM) band
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Physical layer of IEEE 802.11 FHSS
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Physical layer of IEEE 802.11 DSSS
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Physical layer of IEEE 802.11 infrared
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IEEE 802.11 (IEEE 802.11 ( 계속계속 )) Physical layer of IEEE 802.11b
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14.2 BLUETOOTH14.2 BLUETOOTH
Topics discussed in this section:Topics discussed in this section:
BluetoothBluetooth is a wireless LAN technology designed to is a wireless LAN technology designed to connect devices of different functions such as connect devices of different functions such as telephones, notebooks, computers, cameras, printers, telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed network, which means that the network is formed spontaneously. spontaneously.
ArchitectureArchitectureBluetooth LayersBluetooth LayersBaseband LayerBaseband Layer
L2CAPL2CAP
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블루투스블루투스 (( 계속계속 ))
서로 다른 기능을 가진 장치를 연결하기 위해 설계된
무선 LAN 기술
IEEE 802.15 표준안
무선의 개인 영역 네트워크 (PAN, personal area
network) 로 정의
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블루투스블루투스 (( 계속계속 )) Piconet
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블루투스블루투스 (( 계속계속 )) Scatternet
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블루투스블루투스 (( 계속계속 )) Bluetooth layers
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블루투스블루투스 (( 계속계속 )) 무선층 (radio layer)
■ 대역▶ 79 개의 채널의 2.4 GHz ISM 대역
■ FHSS▶ 물리층 의 주파수 도약 확산 스펙트럼 방식▶ 초당 1,600 번 도약▶ 다른 주파수로 도약하기 전 625ms(1/1,600s) 동안 주파수 사용▶ 거주시간 (dwell time) 은 625ms
■ 변조▶ GFSK( 가우시안 대역 필터 ) 라고 불리는 FSK 사용▶ 비트 1 은 반송 주파수보다 높은 값으로 표현▶ 비트 0 은 반송 주파수보다 낮은 값으로 표현
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블루투스블루투스 (( 계속계속 )) 기저대역층 (baseband layer)
■ LAN 에서의 MAC 부계층과 비슷■ 마스터와 슬레브는 타임 슬롯 (time slot) 을 사용 통신■ 타임 슬롯 길이는 거주시간 (625ms) 와 동일
TDMA■ 접근 방식으로 TDMA 사용■ TDD-TDMA(time division duplexing TDMA)■ 반이중 양방향 통신
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블루투스블루투스 (( 계속계속 )) Single-secondary communication
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블루투스블루투스 (( 계속계속 )) Multiple-secondary communication
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블루투스블루투스 (( 계속계속 ))
Frame format types
■ 프레임 형식
▶ 1- 슬롯 626ms – 259ms = 366ms 필요
▶ 2- 슬롯 3×625ms – 259ms = 1,616ms
▶ 5- 슬롯 5×625ms – 259ms = 2,866ms
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블루투스블루투스 (( 계속계속 )) 접근 코드 (access code)
■ 피코넷의 프레임간의 구별
헤더■ 주소 : 7 개까지 슬래이브 지정■ 유형 : 상위 계층 데이터 유형 정의■ F. : 흐름 제어■ A. : 확인 응답■ S. : 순서 번호■ HEC. : 헤더 오류 정정
페이로드■ 0~2,740 비트의 길이
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블루투스블루투스 (( 계속계속 ))
L2CAP data packet format
■ LAN 에서의 LLC 부계층과 비슷
■ 다중화
■ 분할 및 재조립
■ 서비스 품질
■ 그룹 관리
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14.3 14.3 요약요약