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Transcription

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2 ! " % - % 2 % % 4 % % & % ) % * %, % -. % -- % -2 % - % -4 % - 0 "" 1 $ (1 $ $ (1 $ $ ( # $ 5 # $$ # $ ' ( (( +'! $ /0 (1 % +' ( % +' ((!1 3 0

3 ( 6 ' infrastructure network AP AP: Access Point AP wired network AP ad-hoc network Source: Schiller

4 % +' Wireless LAN 2.4 GHz 5 GHz (2 Mbps) b (11 Mbps) g (22-54 Mbps) a (54 Mbps) HiperLAN2 (54 Mbps) HomeRF 2.0 (10 Mbps) Bluetooth (1 Mbps) HomeRF 1.0 (2 Mbps) e (QoS) k (RRM)

5 71 # $ 8 6 " :$6 ; 6 1< =! 1

6 <! 1 A C B Senders A and C separated by obstacle. Each thinks the medium is free. Senders A and C out of range of each other. Each thinks medium is free. A B C

7 =! 1 Range of B A B C sending Range of C D

8 717 = '> ' $6 9 ": A B C Hidden terminal: A is hidden from C s CS ''> ' '" #!!6 #!!8'!'

9 717 = ''% > "" '' #!!8'!''?" (* ? 98?: +$ ''%

10 6<! ' 6 9#! :A 0 " $#!5A 77 9!: < 6 #!! = "#!! 8 B 6A D RTS RTS A B C CTS CTS DATA

11 *.2--C # ' % A"8'!'6'5A ' (6' 6" ' 5' 8'!' A ' 9" 6' : = 6 D' #!! D RTS RTS A B C CTS CTS DATA ACK

12 (*.2--8?92: 7 $ 68(? ( (6 5#!7!78'!'7'8'!'7' (6 65 E Node A Node B CW=7 CW=6 CW=5 CW=4 CW=3 DATA Busy Busy DIFS period

13 (*.2--8?92: 7 $ 68(? ( (6 5#!7!78'!'7'8'!'7' (6 65 E CW=2 CW=1 CW=0 CW=3 Node A DATA DATA ACK RTS CTS Node B DATA Busy Busy RTS CTS DATA ACK DIFS period

14 (*.2--8?9:! $

15 !*.2-- ' 1 ( 6 $ *.2--

16 Beacon PCF DCF Super Frame DCF PCF - Distributed Coordinated Function (Contention Period - Ad-hoc Mode) - Point Coordinated Function (Contention Free Period Infrastructure BSS) Beacon - Management Frame Synchronization of Local timers Delivers protocol related parameters

17 Inter-Frame Spacing : DIFS - 34 µsec PIFS - 25 µsec ( Used in PCF ) SIFS - 16 µsec Slot Time - 9 µsec DIFS = SIFS + (2 * Slot Time) SIFS required for turn around of Tx to Rx and vice versa

18 Data Transmission from Node A to B CW A DIFS ACK DATA A ACK B DIFS SIFS CW Contention Window. Starts only after DIFS. Random number r picked form range ( 0-CW ) CW min minimum value of CW CW max maximum value the CW can grow to after collisions r can be decremented only in CW CW doubles after every collision

19 A Collision between nodes A and C DATA C ACK DATA A DIFS SIFS DIFS Length (DATA A ) = 10 Slot times Length (DATA C ) = 15 Slot times CW after Collision CW after Collision CW after Collision CW after Collision 4 0 6

20 NAV Network Allocation Vector STA A DATA STA B ACK STA C ACK DIFS SIFS DIFS NAV B and C

21 Point Coordinated Function (PCF) Also known as the CFP (Contention Free Period) Operation in an Infrastructure BSS STAs communicate using central authority known as PC (Point Coordinator) or AP (Access Point) No Collisions take place AP takes over medium after waiting a period of PIFS Starts with issue of a Beacon

22 AP taking over the Wireless medium using PIFS DATA A PIFS B DIFS SIFS DIFS DIFS - 34 µsec PIFS - 25 µsec SIFS - 16 µsec Slot Time - 9 µsec B - Beacon

23 (*.2-- '! $ A'

24 1?6! $

25 ' (? (? 9( 7? $: = A 766 DIFS SIFS: Short IFS DIFS PIFS: PCF IFS = SIFS + slot time PIFS DIFS: DCF IFS = SIFS + 2*slot time medium busy SIFS contention next frame Slot time # 766 F.5 % G E A 766H 9:I # 9:H $ F. 5% G % JH% JH% =5% % " % =5 66 time

26 $ '" = busy B1 = 25 wait B1 = 5 data B2 = 20 busy data B2 = 15 wait B2 = 10 cw = 31 B1 and B2 are backoff intervals at nodes 1 and 2

27 A66 ( "! $ 66 "6 ' " $% $" "5% 9. : 6 $ $ 5 $ (*.2-- % $ 6 5%

28 0 ""6(*.2--8? A 66>A A $ CW CW max CW min t

29 (* ? 6(* @,.. E524;E5-;E5);E 300 MHz GHz GHz *.2--$ *.2--

30 * channel# [MHz] channel# center frequency = *channel number [MHz] [MHz]

31 *.2-- K 0?8 " 92. < E: &4H-2< E: 4*54 '" A1&5, * -&73 ' 245& &473 ' 4*54

32 *.2-- '+ ' 8?% '78? ''9 : " " EL766L " '6 $ 8?% '78?#!!9 : "L $" 8?% '7 1?9 : $

33 *.2-- '' '+ 6 " 66 " $566 " $F. 5% G M % 66 " 7 6! 66 ".

34 A66 ( "! $ 66 " 6 ' " $% $" "5% 9. : 6 $ $ 5 $ (*.2-- % $ 6 5%

35 *.2--7??! 65 $ $ 6' ' "5 9 :5A 65 9$: $556 5 bytes Duration/ ID Address 1 Address 2 Address 3 Sequence number Frame Control Address Data 4 CRC bits Protocol version To Type Subtype DS From DS More Frag Power Retry Mgmt More Data WEP Order

36 Table 15.1 Subfields in FC field Type To DS From DS More flag Retry More data WEP Rsvd Field Version Subtype Pwr mgt The current version is 0. Type of information: management (00), control (01), or data (10). Defines the subtype of each type (see ). Defined later. Defined later. When set to 1, means more fragments. When set to 1, means retransmitted frame. When set to 1, means station is in power management mode. When set to 1, means station has more data to send. Wired equivalent privacy. When set to 1, means encryption implemented. Reserved. Explanation

37 Figure Control frames

38 Table 14.2 Values of subfields in control frames Subtype Request to send (RTS) Clear to send (CTS) Meaning Acknowledgment (ACK)

39 Table 15.1 Subfields in FC field To DS From DS Address 1 Destination station Destination station Receiving AP Receiving AP Address 2 Source station Sending AP Source station Sending AP Address 3 BSS ID Source station Destination station Destination station Address 4 N/A N/A N/A Source station

40 Figure Addressing mechanism: case 1

41 Figure Addressing mechanism: case 2

42 Figure Addressing mechanism: case 3

43 Figure Addressing mechanism: case 4

44 ( *.2--6 " *.2-- * ' ""! (1 % 15 % 1 ' " *.2--N= 6 O $6* ; < E O $ 6 $ $ * *.2--K6*.2-- *.2-- < $"-.. $61< P '$6-.. ''1 ( 0 9 ( 0 :5&.. 6 < "5$" 66 *. 2 --( 1 6"6 2.. $"-... K$6*.7,2;< E '

45 (*.2--6 " *.2--A$ 86 6 ' $ = *.2-8 *.2--#$ 8 K 6 $ 5 $@ *.2-- ' C 3 * ' = "@ L Q: 55R ' $ " $ 66 * ( 7' 1 1 ( 7' 1 16= $" = 66 $$ *.2--$8#S2. 24;< ET4 50?8 66* $= -- *.2-- $*.2-- = 6 6* ? 58?@ : 9! 15! 1 :

46 (*.2--6 " *.2--?< " A 56 "6 6 ' 1 9" *. 2 --: "6 66 " "665$5/ (1 % +' < "6. 66 *.2-- $ 8$ 667 6$ $% 8 9% 8: * " * " 6* E 66 *. 2 --( $ = *.2--" $ = 6 $ *.2-- $6 * * ! 5 = * $5 6 6$ L Q 5 $ $$ ( 6 *. 2$--5*.2 5 $$*.2

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