Like ethernet macaw for wireless bharghavan 1 dll ack

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(Like Ethernet). MACAW (for Wireless; Bharghavan ) : 1. DLL “ ACK ” lost frames were not retransmitted: If the transport layer ACKs their absence, it later (delayed time) 2 . ACK (positive) frame after each successful data frame . 3 . Carrier sensing was added . 4 . Run the backoff algorithm separately for each data stream ( source-destination ), rather than for each station. (it reschedules retransmission). 5 . Stations are exchanging information about congestion.
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51 The wireless LAN is described to run at : (802.11), 1 Mbps - or 2 Mbps - too slow, so was needed faster standards. 802.11a, 54 Mbps - uses a wider frequency band. 802.11b , 11 Mbps . uses the same frequency band as 802.11 , but uses different modulation technique, 802.11g, 54 Mbps - which uses the modulation technique as 802.11a but the frequency band of 802.11b.
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52 The 802.11 standard specifies three transmission techniques allowed in the physical layer 1. Use short-range radio, techniques of FHSS 79 hops, 1 MHz wide, PN seq.Dwell time 625 mks, (Bluetooth) 2. Use short-range radio DSSS . 1-2 Mbps, similar to CDMA; bit = 11 chips uses PM . 3. Modifications: 802.11a - 54 Mbps; 802.11b - 11 Mbps; 802.11g - 54 Mbps ? Both of FHSS and DSSS use a part of the unlicensed spectrum (2.4 GHz) ISM ( Industrial, Scientific, and Medical ) application band. The infrared method : as television remote control 0.85 nm, 1-2 Mbps 11 1 Mbps or 2 Mbps, so was too slow. 11a FHSS; 5-GHz band ; 54 Mbps ; OFDM ( 48 data+ 4 Sync) ch. 18-54 Mbps, = With Europ. HiperLAN/2 11b DSSS ; Uses the same frequency band as 802.11 , but uses different modulation technique achieve: 1, 2, 5.5, 11 Mbps. 11g Uses the OFDM modulation= 802.11a but the frequency band =of 802.11b . ( Theory-54 Mbps)?? 16 10-to-66 GHz frequency range
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53 802.11 Modifications 11 1 Mbps or 2 Mbps, so was too slow. 11a FHSS; 5-GHz band ; 54 Mbps ; OFDM ( 48 data+ 4 Sync) ch. 18-54 Mbps, =With Europ. HiperLAN/2 11b DSSS ; Uses the same frequency band as 802.11 , but uses different modulation technique achieve: 1, 2, 5.5, 11 Mbps. 11g Uses the OFDM modulation= of 802.11a but the frequency band =of 802.11b . ( Theory-54 Mbps)?? 16 10-to-66 GHz frequency range
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54 Medium Access with CSMA/CA When many users are located in the same area, and use the same wireless LAN at the same time, two different MAC methods are defined for signal multiplexing: 1. Distributed Coordination Function (DCF) ( no control ) 2. Point Coordination Function (PCF) ( BS controls cell ) The basic access mechanism, called the DCF , Each unit senses the medium before it starts to transmit. If the medium is free for several microseconds, the unit can transmit for a limited time . If the medium is busy , the unit will back-off for a random time before it senses again. It does not sense the channel while transmitting ,
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55 Medium Access with CSMA/CA (Cont) The basic access mechanism : DCF = CSMA/CA algorithm: 2 methods . 1). Physical channel sensing. 2). Virtual channel sensing 1. Physical channel sensing (PCS): Like Ethernet It does not sense the channel while transmitting , a) CSMA/CD needs full-duplex channel b) 802.11 all stations cannot hear each other 802.11 =802.3 + Positive Acknowledge Scheme 2. MACAW-Virtual Carrier Sense (VCS )
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56 The802.11 MAC Protocol (MACAW) 2. MACAW-Virtual Carrier Sense (VCS) using CSMA/CA .
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