The IEEE (Institute of Electrical and Electronics Engineers) Standards Association, http://standards.ieee.org/, likes to designate standards using numbers rather than names. Within the IEEE schema, the number 802 is used to designate local area networks and metropolitan, or wide area, networks (LANs and WANs). 802.11 is the name for wireless LAN specifications in general. There are a number of different flavors of the 802.11 standards, such as 802.11b, 802.11g, and so on, that I'll discuss later in this Appendix in more detail. Each of these particular versions of the wireless LAN specification (802.11) runs on the 2.4GHz or the 5GHz spectrums at high speeds.
To understand 802.11, it's important to understand the purpose of the general wireless LAN standard. According to the original Project Authorization Request, "the scope of the proposed standard is to develop a specification for wireless connectivity for fixed, portable, and moving stations within a local area." In addition, "...the purpose of the standard is to provide wireless connectivity to automatic machinery and equipment or stations that require rapid deployment, which may be portable, handheld, or which may be mounted on moving vehicles within a local area."
The 802.11 standards specify a Medium Access Control (MAC) layer and a Physical (PHY) layer using Direct Sequence Spread Spectrum (DSSS) technology.
The MAC layer is a set of protocols that are responsible for maintaining order in the use of a shared medium. For example, data encryption is handled in the MAC.
The PHY layer handles transmission between nodes (or devices on the network). In other words, it is primarily concerned with hardware.
DSSS is a technique for splitting up and recombining information to prevent collisions between different data streams. Effectively, if my network is using DSSS and encounters other signals on the same spectrum it is using, my network can use DSSS to avoid interference from the other signals.
The MAC and PHY layers fit within the generalized OSI (Open System Interconnection) reference model. The OSI model is a way of describing how different applications and protocols interact on network-aware devices.
The primary purpose of 802.11 is to deliver MAC Service Data Units (MSDUs) between Logical Link Controls (LLCs). Essentially, an LLC is a base station with a wireless access point, which itself may be connected to a wire line network for hand-off to additional wireless LLCs.
802.11 networks operate in one of two modes: "infrastructure" and "ad hoc." The infrastructure architecture is used to provide network communications between wireless clients and wired network resources. An ad hoc network architecture is used to support mutual communication between wireless clients. It is typically created spontaneously, does not support access to wired networks, and does not require an access point to be part of the network.
The PHY layer of 802.11 defines three physical characteristics for wireless local area networks:
Direct Sequence Spread Spectrum (the primary technique for avoiding signal interference in today's 802.11 networks)
Frequency Hopping Spread Spectrum (which is another technique for avoiding interference)
Okay! Enough jargon, acronyms, and theoretical engineering. Let's get on to the flavors of 802.11.