IEEE 802 11 Overview Onno W Purbo Onnoindo

IEEE 802. 11 Overview Onno W. Purbo Onno@indo. net. id

Context Application n Wireless Differences n Presentation n Session n Transport n Network Link LLC MAC Physical PHY OSI Power management Bandwidth Security addressing 802. 2 802. 3 802. 4 802. 5 802. 11 IEEE

Logical Link Control Services Upper Layer 802. 2 802. 11 Unack Connectionless Oriented Ack Connectionless 802. 11

Topology BSS AP DS AP BSS Basic Service Set (BSS) Extended Service Set (ESS)

Independent BSS

Extended Service Set

Topology Characteristics n Mobility n n No transitions BSS transition ESS transition (not guaranteed) Within ESS n n n BSSs that are partially overlap BSSs that are physically disjoint BSSs that are physically collocated

Logical Architecture n n LLC CSMA/CA MAC DSSS FHSS Service primitives IR 2. 4 GHz 1 W 300 meter n n n Request Confirm Indication responds

802. 11 services n Station Services n n Authentication, deauthentication, privacy (WEP), MSDU delivery. Disrtibuted System Services n Association, deassociation, distribution, integration, reassociation.

How does a station join a BSS? n Scanning n n Passive Active Authentication Association

MAC Details n CSMA/CA (time slot = 20 us) n n Priority Based n n Distributed Coordination Function (DCF). Virtual carrier sense (RTS/CTS) Exponential random backoff algorithm. Point Coordination Function (PCF). Segmentation & Reassembly.

Physical – DSSS details n n n 2 Mbps w/DQPSK or 1 Mbps w/DBPSK 14 channels (11 channels for US). 5 plans – 3 max. non-overlapping channels.

Physical – FHSS details n n n 1 Mbps w/ 2 level GFSK 79 1 Mbps channels (2. 402 – 2. 480 GHz) 78 sequences (3 sets of 26) Minimum hop rate = 2. 5 hop/s Minimum hop distance = 6 MHz

802. 11 Future n 802. 11 a n n 802. 11 b n n High data rates 2. 4 GHz band: 5 GHz band: 20 Mbps High data rates 2. 4 GHz band: FH 4. 5 Mbps: DS 25. 5 Mbps WPAN n Wearable Devices (30 feet, 1 Mbps, 0. 5 in 3, lower power, low cost).