WLAN Terminology and Technology

1. WLAN Terminology and Technology • Active and passive scanning • Power saving operation • Data rates and throughput • Dynamic rate and switching • Authentication and association • The distribution system and roaming • Infrastructure and ad hoc modes • BSSID, SSID, BSS, ESS • Protection mechanisms

2. Exam Essentials • Understand the different operation modes for IEE 802.11 wireless networks • Be familiar with the different service sets used with WLANs • Indentify the terminology used with IEEE 802.11. WLANs • Know the process devices use to join a WLAN • Understand the differences between distribution systems as well as data transfer • Indentify the power save capabilities of IEEE 802.11 WLANs • Know the various protection mechanisms available for both IEEE 802.11g and 802.11n WLANs

3. WLAN Modes of Operation • Independent basic service set (IBSS) • Basic service set (BSS) • Extended service set (ESS)

4. Independent basic service set (IBSS) • No access point • Independent or autonomous devices (clients) • Three parameters for IBSS participation • SSID • RF Channel • Security configuration

5. Service Set Identifier (SSID) • Name of the service set used to identify the WLAN and for device segmentation

6. Radio Frequency (RF) Channel • Channel specified on the client and/or AP configuration over which devices will communicate • ISM • channels 1-11 • UNNII • channels 1-4

7. IBSS Security • Configurable and is not mandated by devices, AP or other WLAN hardware. • IBSS has no inherent security

8. Advantages and Disadvantages of IBSS • Easy to configure • Inexpensive to deploy • Limited range • No centralized admin • Not scalable • Difficult to secure

9. Basic Service Set (BSS) • Foundation of distributive WLANs • Access point (AP) • Client devices • Similar parameters to IBSS • SSID • RF Channel • Security configuration

10. Advantages and Disadvantages of BSS • Flexible in various situations, homes, SOHO, small enterprises • Scalable • Centralized admin • Security parameters • Additional hardware costs (APs etc.) • Require site survey • Must connect to a larger infrastructure • Technical expertise

11. Extended Service Set (ESS) • One or more connected BSS • Requires a layer two or layer three devices for connectivity

12. Connecting to a WLAN • Frame types • Management frames • Beacon, probe request, authentication, association request, association response • Control frames • RTS (request to send), CTS (clear to send), ACK • Data frames • Carries the payload

13. Connecting to a WLAN • Passive scanning • 1st part of the discovery phase of WLAN • Listening for AP SSIDs • Active scanning • 2nd part of the discovery phase • Device finds a network and sends out a probe request “May I join your WLAN?”

14. Connecting to a WLAN • Authentication • Open system authentication • May I join your WLAN – Sure come on in • Shared key authentication • May I join your WLAN – Sure, what’s the secret password • Association • If authentication is correct then free association with the network is allowed.

15. Connecting to a WLAN • Deauthentication • Authentication no longer valid • Logging off • Roaming to a different BSS • Disassociation • When an association is terminated

16. Distribution System • Connection of one or more BSS • APs • Wired • Wireless

17. Data Rates • Established rate of data exchanged between devices • Subjective

18. Data Rates

19. Throughput • Actual rate of data exchanged • Dependent on • Spread spectrum or technology (standard/amendment) • RF interference • Number of simultaneous users connected to the AP

20. Dynamic Rate Switching • A.K.A dynamic rate selection • Allows a device to adapt to a certain BSS configuration

21. WLAN Roaming • Moving from one BSS to another • Device needs to decide which BSS to access if two or more are available • Criteria • Signal strength • Signal to noise ratio • Error rate • Number of currently associated devices

22. Power Saving Options • Many WLAN devices are portable and utilize DC batteries • Device configurable • E.g. Windows XP Advanced Power Management (APM)

23. Power Saving Options • Active Mode (AM) • Not using batteries • Power Save (PS) Mode • Doze or enter a low power state • Activated manually or through a listening state • Automatic Power Save Delivery (ASPD) • Awakened by a trigger frame to receive data

24. Protection Mechanisms • Compatibility standards between newer/faster devices and slower/legacy systems • Extended rate physical (ERP) protection • High throughput (HT) protection

25. Extended Rate Physical (ERP) Protection • 802.11b only mode • DSSS and HR/DSSS • 1, 2, 5.5 and 11 Mbps • 802.11g only mode • ERP-OFDM • 6, 9, 12, 18, 24, 36, 48, and 54 Mbps • 802.11b/g mixed mode • DSSS, HR/DSSS and ERP-OFDM • 1, 2, 5.5 and 11 Mbps • 6, 9, 12, 18, 24, 36, 48, and 54 Mbps

26. High Throughput (HT) Protection • 802.11n devices operate in ISM and UNII • Mode 0 • Greenfield - 802.11n devices only • Mode 1 • HT Non-member Protection Mode – switches when 802.11a/b/g device is detected • Mode 2 • HT 20 MHz Protection Mode – 802.11n device only, that can use 20 MHz or 40 MHz wide channels • Mode 3 • HT Mixed Mode – used if one of more non-HT devices are associated to the BSS.

27. Protection Mechanisms • Two new protection standards • Dual CTS – layer 2 protection between HT and non-HT devices • PCO – alternates between 20 MHz and 40 MHz versus one or the other

28. Exam Essentials • Understand the different operation modes for IEE 802.11 wireless networks • Be familiar with the different service sets used with WLANs • Indentify the terminology used with IEEE 802.11. WLANs • Know the process devices use to join a WLAN • Understand the differences between distribution systems as well as data transfer • Indentify the power save capabilities of IEEE 802.11 WLANs • Know the various protection mechanisms available for both IEEE 802.11g and 802.11n WLANs