5.1 General description of the architecture
This clause presents the concepts and terminology used within this standard. Specific terms are defined in Clause 3. Illustrations convey key IEEE 802.11 concepts and the interrelationships of hearchitectural components. IEEE Std 802.11 uses an architecture to describe functional componentsof an IEEE 802.11 LAN. The architectural descriptions are not intended to represent anyspecific physical implementation of IEEE Std 802.11.
5.1.1 How WLAN systems are different
Wireless networks have fundamental characteristics that make them significantly different fromtraditional wired LANs. Some countries impose specific requirements for radio equipment inaddition to those specified in this standard. This standard does not provide information to meet these country-specific radio regulations.
5.1.1.1 Destination address does not equal destination location
In wired LANs, an address is equivalent to a physical location. This is implicitly assumed in the designof wired LANs. In IEEE Std 802.11, the addressable unit is a station (STA). The STA is a message destination, but not (in general) a fixed location.
5.1.1.2 Media impact on design and performance
- The PHYs used in IEEE Std 802.11 are fundamentally different from wired media. Thus IEEE 802.11 PHYs
a) Use a medium that has neither absolute nor readily observable boundaries outside of which STAs with conformant PHY transceivers are known to be unable to receive network frames
b) Are unprotected from other signals that may be sharing the medium
c) Communicate over a medium significantly less reliable than wired PHYs
d) Have dynamic topologies
e) Lack full connectivity, and therefore the assumption normally made that every STAcanheareveryother STA is invalid (i.e., STAs may be “hidden” from each other)
f) Have time-varying and asymmetric propagation properties
g) May experience interference from logically disjoint IEEE 802.11 networks operating in overlapping areas
- Because of limitations on wireless PHY ranges, WLANs intended to cover reasonable geographic distances may be built from basic coverage building blocks. When providing QoS services it should beunderstood that the MAC endeavors to provide QoS “service guarantees” within the limitations of the medium properties identified above. In other words, particularlinunlicensedspectrutrueguarantees are often not possible. However, gradations of service are always possible; and in sufficiently controlled environments, QoS guarantees can truly be made.
5.1.1.3 The impact of handling mobile STAs
- One of the requirements of IEEE Std 802.11 is to handle mobile as well as portable STAs. A portableSTA is one that is moved from location to location, but that is only used while at a fixed location. Mobile STAs actually access the LAN while in motion.
- For technical reasons, it is not sufficient to handle only portable STAs. Propagation effects blur the distinction between portable and mobile STAs; stationary STAs often appear to be mobile due to propagation effects. Another aspect of mobile STAs is that they may often be battery powered. Hencepower management isan important consideration. For example, it cannot be presumed that aSTA’s receiver will always bepowered on.
5.1.1.4 Interaction with other IEEE 802® layers
- IEEE Std 802.11 is required to appear to higher layers [logical link control (LLC)] as a wired IEEE 802LAN. This requires that the IEEE 802.11 network handle STA mobility within the MAC sublayer. Tomeetreliability assumptions (that LLC makes about lower layers), it is necessary for IEEE Std 802.11 to incorporate functionality that is untraditional for MAC sublayers.
- In a robust security network association (RSNA), IEEE Std 802.11 provides functions to protect dataframes, IEEE Std 802.1X-2004 provides authentication and a Controlled Port, and IEEE Std 802.11and IEEE Std 802.1X-2004 collaborate to provide key management. All STAs in an RSNA have acorresponding IEEE 802.1X entity that handles these services. This standard defines how an RSNA utilizes IEEE Std 802.1X-2004 to access these services.
- When used to support applications with QoS requirements, each IEEE 802.11 LAN provides a linkwithin an end-to-end QoS environment that may be established between, and managed by, higherlayer entities. To handle QoS traffic in a manner comparable to other IEEE 802 LANs, the IEEE802.11 QoS facility requires the IEEE 802.11 MAC sublayers to incorporate functionality that is nottraditional for MAC sublayers.Inaddition,itmaybenecessaryorcertainhigherlayermanagemententities to be “WLAN aware” at least to the extent of understanding that the available bandwidth and other QoS characteristics of a WLAN are subject to frequent,andsometimessubstantial, dynamic changes due to causes other than traffic load and are outside thedirect control of network management entities.
5.1.1.5 Interaction with non-IEEE-802 protocols
An RSNA utilizes non-IEEE-802 protocols for its authentication and key management (AKM) services.
Some of these protocols are defined by other standards organizations, such as the Internet Engineering Task Force (IETF).
