IEEE 802.11 WLAN

Association Response

Modulations

IEEE Standards

802.11b

11 Mbps

2.4 GHz

DSSS

11/13

1999

802.11g

54 Mbps

2.4 GHz

DSSS/OFDM

11/13

2003

802.11n

300 Mbps

2.4/5 GHz

OFDM

32/32

2009

WLAN Components

IBSS

ESS

BSS

BSS

DS

Basic Service Area (BSA)

The physical area covered by the wireless signal of a BSS

Basic Service Set (BSS)

A set of stations and/or access points which can directly

communicate via a wireless medium

Distribution System (DS)

The wired infrastructure connecting multiple BSSs to form an ESS

Extended Service Set (ESS)

A set of multiple BSSs connected by a DS which appear to wireless

stations as a single BSS

Independent BSS (IBSS)

An isolated BSS with no connection to a DS; an ad hoc WLAN

Measuring RF Signal Strength

Decibel (dB)

An expression of signal strength as compared to a reference signal;

calculated as 10log10(signal/reference)

dBm · Signal strength compared to a 1 milliwatt signal

dBw · Signal strength compared to a 1 watt signal

dBi · Compares forward antenna gain to that of an isotropic antenna

Scheme

Modulation

Throughput

Terminology

DSSS

OFDM

DBPSK

DQPSK

CCK

BPSK

QPSK

1 Mbps

2 Mbps

5.5/11 Mbps

6/9 Mbps

12/18 Mbps

16-QAM

24/36 Mbps

64-QAM

48/54 Mbps

by Jeremy Stretch

Basic Service Set Identifier (BSSID)

A MAC address which serves to uniquely identify a BSS

Service Set Identifier (SSID)

A human-friendly text string which identifies a BSS; 1-32 characters

Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)

The mechanism which facilitates efficient communication across a

shared wireless medium (provided by DCF or PCF)

Effective Isotropic Radiated Power (EIRP)

Net signal strength (transmitter power + antenna gain - cable loss)

v2.2

IEEE 802.11 WLAN · PART 2

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Distributed Coordination Function (DCF)

DIFS

DIFS

DIFS

DIFS

A

B

C

D

Frame

Deferral Period

Random Backoff

Contention Window

Interframe Spacing

Client Authentication

Short IFS (SIFS)

Used to provide minimal spacing delay between

control frames or data fragments

DCF IFS (DIFS)

Normal spacing enforced under DCF for management

and non-fragment data frames

Arbitrated IFS (AIFS)

Variable spacing calculated to accommodate differing

qualities of service (QoS)

Extended IFS (EIFS)

Extended delay imposed after errors are detected in a

received frame

Encryption Schemes

Wired Equivalent Privacy (WEP)

Flawed RC4 implementation using a 40- or 104-bit

pre-shared encryption key (deprecated)

Wi-Fi Protected Access (WPA)

Implements the improved RC4-based encryption

Temporal Key Integrity Protocol (TKIP) which can

operate on WEP-capable hardware

IEEE 802.11i (WPA2)

IEEE standard developed to replace WPA; requires a

new generation of hardware to implement significantly

stronger AES-based CCMP encryption

Open · No authentication is used

Pre-shared Encryption Keys

Keys are manually distributed among clients and APs

Lightweight EAP (LEAP)

Cisco-proprietary EAP method introduced to provide

dynamic keying for WEP (deprecated)

EAP-TLS

Employs Transport Layer Security (TLS); PKI

certificates are required on the AP and clients

EAP-TTLS

Clients authenticate the AP via PKI, then form a secure

tunnel inside which the client authentication takes

place (clients do not need PKI certificates)

Protected EAP (PEAP)

A proposal by Cisco, Microsoft, and RSA which employs

a secure tunnel for client authentication like EAP-TTLS

EAP-FAST

Developed by Cisco to replace LEAP; establishes a

secure tunnel using a Protected Access Credential

(PAC) in the absence of PKI certificates

RF Signal Interference

Reflection

Scattering

Absorption

WMM

Platinum

Gold

Silver

Bronze

Quality of Service Markings

802.11e

802.1p

7/6

5/4

3/0

2/1

6/5

4/3

0

2/1

Refraction

Diffraction

Wi-Fi Multimedia (WMM)

A Wi-Fi Alliance certification for QoS; a subset of

802.11e QoS

IEEE 802.11e

Official IEEE WLAN QoS standard ratified in 2005;

replaces WMM

IEEE 802.1p

QoS markings in the 802.1Q header on wired Ethernet

Antenna Types

Directional · Radiates power in one focused direction

Omnidirectional

Radiates power uniformly across a plane

Isotropic

A theoretical antenna referenced when measuring

effective radiated power

by Jeremy Stretch

v2.2