mobile communication

3. Software and HW Access Point HW Access Point

8. Extension Point

9. Roaming

11. LAN to LAN Wireless Communication Each Access Point acts as a Router or Bridge to connect its own LAN to the wireless network

12. Mobile Communication Technology according to IEEE Local wireless networks WLAN 802.11 802.11a 802.11b 802.11i/e/…/w 802.11g WiFi 802.11h 802.15.4 802.15.1 802.15.2 Bluetooth 802.15.4a/b ZigBee 802.15.3 802.20 (Mobile Broadband Wireless Access) + Mobility WiMAX 802.15.3a/b 802.15.5

18. Comparison: infrastructure vs. ad-hoc networks Infrastructure network ad-hoc network AP AP AP wired network AP: Access Point

24. IEEE standard 802.11 mobile terminal access point fixed terminal application TCP 802.11 PHY 802.11 MAC IP 802.3 MAC 802.3 PHY application TCP 802.3 PHY 802.3 MAC IP 802.11 MAC 802.11 PHY LLC infrastructure network LLC LLC

31. PHY : DSSS Sync SFD signal service length HEC Payload 128 16 8 8 16 16 Variable Uses 11-chip Barker Code : +1 -1 +1 +1 -1 +1 +1 +1 -1 -1 -1 Start Frame Delimiter(SFD) : 1111001110100000 Signal : Data Rate of Payload 0x0A : 1Mbps; 0x14 : 2Mbps Service : Future use; 0x00 : indicates IEEE 802.11 compliant Length(16 bits) : Length of payload HEC; Header error check : CRC 16 polynomial for signal, service and length fields Payload

33. Medium Access Medium Busy Contention next frame Time DIFS Direct Access if “Medium is Free” >= DIFS DIFS PIFS SIFS Short Interframe Spacing (SIFS) : Highest priority, acks, polling responses PCF Inter-frame spacing (PIFS): medium priority, time bounded service DCF Inter-frame Spacing (DIFS) : Asynchronous data service within a contention period – lowest priority

38. 802.11 - competing stations - simple version(for broadcast) t busy bo e station 1 station 2 station 3 station 4 station 5 packet arrival at MAC DIFS bo e bo e bo e busy elapsed backoff time bo r residual backoff time busy medium not idle (frame, ack etc.) bo r bo r DIFS bo e bo e bo e bo r DIFS busy busy DIFS bo e busy bo e bo e bo r bo r

45. Fragmentation t SIFS DIFS data ACK 1 other stations receiver sender frag 1 DIFS contention RTS CTS SIFS SIFS NAV (RTS) NAV (CTS) NAV (frag 1 ) NAV (ACK 1 ) SIFS ACK 2 frag 2 SIFS

47. DFWMAC-PCF I PIFS stations‘ NAV wireless stations point coordinator D 1 U 1 SIFS NAV SIFS D 2 U 2 SIFS SIFS SuperFrame t 0 medium busy t 1

50. DFWMAC-PCF II t stations‘ NAV wireless stations point coordinator D 3 NAV PIFS D 4 U 4 SIFS SIFS CF end contention period contention free period t 2 t 3 t 4

56. MAC address format DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address

59. Synchronization using a Beacon (infrastructure) beacon interval t medium access point busy B busy busy busy B B B value of the timestamp B beacon frame

61. Synchronization using a Beacon (ad-hoc) t medium station 1 busy B 1 beacon interval busy busy busy B 1 value of the timestamp B beacon frame station 2 B 2 B 2 random delay

64. Power saving with wake-up patterns (infrastructure) .........Only One Station Shown........... TIM interval t medium access point busy D busy busy busy T T D DTIM interval B B station p d d T TIM D DTIM B broadcast/multicast awake p PS poll d data transmission to/from the station

66. Power saving with wake-up patterns (ad-hoc) awake D transmit data t station 1 B 1 B 1 B beacon frame station 2 B 2 B 2 random delay A a D d ATIM window beacon interval a acknowledge ATIM d acknowledge data A transmit ATIM