802.11 Network Structures

zuallererst sollten wir mal die struktur festlegen (is jetz die ausm skript), sprich sachen rausstreichen, dann den ganzen kram befüllen ...--Cb 20:52, 11 July 2006 (CEST)

Traditional 802.11

• 802.11 =
  • „wireless ethernet“
  • Wi-fi (from Wi-Fi Alliance, wireless fidelity)

IEEE 802.11 as part of IEEE 802

• IEEE 802.11x =
  • IEEE = Institute of Electronics and Electrical Engineers
  • 802 = project group (Entwicklung von LAN-Standards)
  • 11 = working group (Entwicklung eines wireless-LAN Standards)
  • x = task groups
• erstmalige Spezifikation 1997, Änderungen 802.11-1999, 802.11-2003
• the 802.11 Task Groups:

802.11	First standard (1997). Specified the MAC and the original slower frequency-hopping and direct-sequence modulation techniques.
802.11a	Second physical layer standard (1999), but products not released until late 2000.
802.11b	Third physical layer standard (1999), but second wave of products. The most common 802.11 equipment as the first book was written.
TGc	Task group that produced a correction to the example encoding in 802.11a. Since the only product was a correction, there is no 802.11c.
802.11d	Extends frequency-hopping PHY for use across multiple regulatory domains.
TGe (future 802.11e)	Task group producing quality-of-service (QoS) extensions for the MAC. An interim snapshot called Wi-Fi Multi-Media (WMM) is likely to be implemented before the standard is complete.
802.11F	Inter-access point protocol to improve roaming between directly attached access points.
802.11g	Most recently standardized (2003) PHY for networks in the ISM band.
802.11h	Standard to make 802.11a compatible with European radio emissions regulations. Other regulators have adopted its mechanisms for different purposes.
802.11i	Improvements to security at the link layer.
802.11j	Enhancements to 802.11a to conform to Japanese radio emission regulations.
TGk (future 802.11k)	Task group to enhance communication between clients and network to better manage scarce radio use.
TGm	Task group to incorporate changes made by 802.11a, 802.11b, and 802.11d, as well as changes made by TGc into the main 802.11 specification. (Think "m" for maintenance.)
TGn (future 802.11n)	Task group founded to create a high-throughput standard. The design goal is throughput in excess of 100 Mbps, and the resulting standard will be called 802.11n.
TGp (future 802.11p)	Task group adopting 802.11 for use in automobiles. The initial use is likely to be a standard protocol used to collect tolls.
TGr (future 802.11r)	Enhancements to roaming performance.
TGs (future 802.11s)	Task group enhancing 802.11 for use as mesh networking technology.
TGT (future 802.11T)	Task group designing test and measurement specification for 802.11. Its results will be standalone, hence the uppercase letter.
TGu (future 802.11u)	Task group modifying 802.11 to assist in interworking with other network technologies.

• Beziehung von 802.11 zum ISO/OSI-Modell:

• • IEEE 802 Spezifikationen beziehen sich nur auf 2 untersten OSI-Layer -> Physical + Data Link Layer
  • = MAC + PHY (physical) Komponente
  • physical Layers:
    • FHSS – frequency-hopping spread-spectrum
    • DSSS – direct-sequence spread-spectrum
    • mit 802.11b -> HR/DSSS – high-rate DSSS
    • mit 802.11a -> OFDM – orthogonal frequency division multiplexing
    • 802.11g abwärts-kompatibel zu b, nutzt ausserdem auch OFDM

Structure of a wireless network

• Stationen
  • Computer im WLAN
• Access Points
  • Bridges: Station <-> Station bzw Station <-> Externe Hosts
  • ursprünglich ein Gerät, neuerdings auch „thin“ APs und AP-Controller
• Drahtloses Medium
• DS – Verteilungssystem

Types of Networks

Es gibt mehrere Arten, die Unterschiede aufweisen und teilweise voneinander abhängen.

Grundlage eines wireless LAN ist das BSS:

• Gruppe von Stationen, die miteinander kommunizieren
• Kommunikation innerhalb der BSA (Basic Service Area), durch Ausbreitungseigenschaften der Funkstrahlen definierter Raum.

Independent BSS (IBSS, Ad-Hoc networks)

• direkte Kommunikation der Stationen
• typischerweise für wenige Stationen bzw. geringen Zeitraum etabliert

Network operations and services

Management

Scanning a Network: Probes and Beacons

Passive Scanning Active Scanning Beacon Frame Probe Request Frame Probe Response Frame Scan Report

Joining a network

1.4.3.2.1 802.11 Authentication 21 1.4.3.2.2 Preauthentication 22 1.4.3.2.3 Association Procedure 22 1.4.3.2.4 Association Request Frame 22 1.4.3.2.5 Association Response Frame 23 1.4.3.2.6 Mobility support: Transitions 23 1.4.3.2.7 Reassociation procedure 24 1.4.3.2.8 Reassociation Request Frame 25 1.4.3.2.9 Association and authentication states 25

Moving data

Prinzipien

1.4.6.1.1 Broadcast Data, Multicast Data und Management Frames 29 1.4.6.1.2 Unicast Data (Management und Daten) 30 1.4.6.1.3 PowerSave Sequenzen 31

Integration/Encapsulation of ethernet frames

1.4.6.4.1 Prinzip 33 1.4.6.4.2 Ablauf des Bridging zwischen 802.11 und Ethernet 34 wireless2wired 35 wired2wireless 35