L7a_wlan2 - EEC173B/ECS152C, Spring 2010 802.11 Frame...

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Page 1 EEC173B/ECS152C, Spring 2010 IEEE 802.11 (Cont’d) 802.11 Frame format 802.11 MAC management Synchronization, Handoffs, Power Advanced Topics Security QoS Throughput 2 802.11 Frame format Frame Types Data: unicast (ACKed); broadcast/multicast (not ACKed) Control: RTS/CTS, ACKs Management (beacon, probe request/response, authentication, association, etc) Sequence numbers Important against duplicated frames due to lost ACKs Addresses Receiver, transmitter (physical), BSS identifier, sender (logical) Miscellaneous Sending time, checksum, frame control, data 3 802.11 Frame format Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Data CRC 2 2666 6 24 0-2312 bytes Protocol version Type Subtype To DS More Frag Retry Power Mgmt More Data WEP 224 1 From DS 1 Order b i t s 11111 1 4 MAC Address Format scenario to DS from DS address 1 address 2 address 3 address 4 ad-hoc network 0 0 DA SA BSSID - infrastructure network, from AP 0 1 DA BSSID SA - infrastructure network, to AP 1 0 BSSID SA DA - infrastructure network, within DS 1 1 RA TA DA SA DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address 5 Special Frames: ACK, RTS, CTS Acknowledgement Request To Send Clear To Send Frame Control Duration Receiver Address Transmitter Address CRC 2 266 4 bytes Frame Control Duration Receiver Address CRC 2 264 bytes Frame Control Duration Receiver Address CRC 2 bytes ACK RTS CTS EEC173B/ECS152C, Spring 2009 Wireless LANs Evolution of Technology & Standards IEEE 802.11 Design Choices Architecture & Protocols PHY layer MAC layer design 802.11 Frame format 802.11 MAC management Synchronization, Handoffs, Power Acknowledgment: Selected slides from Prof. Schiller & Prof. A. Joseph
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Page 2 7 802.11 MAC Management Sublayer Registration/Synchronization Try to find a LAN, try to stay within a LAN Timer, etc. Handoff: Association/Reassociation Integration into a LAN Roaming, i.e. change networks by changing access points Scanning, i.e. active search for a network Power management Sleep mode without missing a message Periodic sleep, frame buffering, traffic measurements Security MIB Management Information Base Managing, read, write 8 Registration A management frame called beacon is transmitted periodically by the AP to establish the timing synchronization function (TSF) TSF contains: BSS id, timestamp, traffic indication map (TIM), power management, and roaming information RSS measurements are done on the beacon message Association: process by which an MS registers with an AP 9 Synchronization using a Beacon (infrastructure) beacon interval t medium access point busy B busy busy busy B B B valueofthetimestamp B beacon frame 10 Synchronization using a Beacon (ad hoc) t medium station 1 busy B 1 beacon interval busy busy busy B 1 B beacon frame station 2 B 2 B 2 random delay 11 Handoff Mobility Types:
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This note was uploaded on 04/29/2010 for the course ECS 152 taught by Professor Mr. during the Spring '10 term at University of Great Falls.

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L7a_wlan2 - EEC173B/ECS152C, Spring 2010 802.11 Frame...

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