The IEEE 802.11 standard defines the foundational elements for wireless local area networking at the Physical (PHY) and Medium Access Control (MAC) layers. It primarily governs the operation in unlicensed frequency bands.

● Station (STA): The fundamental device in any 802.11 network. A STA is any device that contains an 802.11 compliant wireless network interface controller (NIC) and can connect to a Wi-Fi network. This includes client devices (laptops, smartphones, tablets, IoT devices) and Access Points themselves. Each STA is identified by its unique 48-bit MAC address.

● Access Point (AP): The central coordinating device in an infrastructure-based 802.11 WLAN. An AP acts as a bridge between the wireless medium and a wired backbone network (typically Ethernet). Key functions of an AP include:
○ Beacon Transmission: Periodically broadcasting its presence and network parameters.
○ Medium Access Coordination: Facilitating and managing access to the shared wireless medium for associated STAs.
○ Buffering and Forwarding: Buffering frames for power-saving STAs and forwarding frames between associated STAs and the wired network.
○ Security Services: Implementing authentication (e.g., 802.1X, PSK) and encryption (e.g., WPA2, WPA3).
○ Association Management: Handling association and reassociation requests from STAs.

● Basic Service Set (BSS): The fundamental building block of an 802.11 WLAN. A BSS defines a group of wireless STAs that can communicate with each other.
○ Infrastructure BSS: The most common type. It consists of a single Access Point (AP) and all the wireless STAs that are associated with it. All communication between STAs within an Infrastructure BSS, or between an STA and any external network, must pass through the AP. The AP serves as the central coordinator.
○ Independent BSS (IBSS) / Ad-hoc Network: Consists of two or more STAs communicating directly with each other without the need for an AP. This is a peer-to-peer network. IBSSs are typically temporary and limited in range, as they lack the coordination and bridging capabilities of an AP.
○ Basic Service Set Identifier (BSSID): A unique 48-bit identifier for a BSS. For an Infrastructure BSS, the BSSID is typically the MAC address of the Access Point's wireless interface. For an IBSS, a randomly generated MAC address is used.

● Service Set Identifier (SSID): A human-readable, user-defined name (up to 32 characters) that logically identifies a particular WLAN. It is often referred to as the "network name" or "Wi-Fi name" (e.g., "Corporate_Network," "Guest_Wi-Fi").
○ STAs use the SSID to identify and select the network they wish to connect to.
○ While an SSID identifies a logical network, multiple APs within an Extended Service Set (ESS) can broadcast the same SSID to provide seamless roaming.
○ An AP can also be configured to broadcast multiple SSIDs simultaneously, each mapped to a different Virtual Local Area Network (VLAN) for segmenting traffic or applying different security policies.
○ SSID Hiding (Disabling SSID Broadcast): An AP can be configured not to broadcast its SSID in beacon frames. While this might seem like a security measure, it offers very little actual security and can complicate client discovery.

● Extended Service Set (ESS): A larger wireless network formed by interconnecting two or more Infrastructure BSSs (each with its own AP). All APs within an ESS share the same SSID.
○ Purpose: To extend the coverage area of a WLAN beyond the range of a single AP and to provide seamless roaming for wireless clients. As a client moves from the coverage area of one AP to another within the same ESS, it can seamlessly transition its association (reassociation) without losing network connectivity (e.g., an ongoing VoIP call or video stream).
○ Distribution System (DS): The underlying wired (most commonly Ethernet) or logical wireless network that connects all the APs within an ESS. The DS allows frames to be transferred between different BSSs and between APs and the wired network backbone, providing connectivity to external resources like the Internet.

● Channels and Channel Planning:
○ Frequency Bands: 802.11 networks operate in specific unlicensed radio frequency bands: 2.4 GHz, 5 GHz, and 6 GHz.
○ Channels: Each band is divided into discrete frequency ranges called channels.
■ 2.4 GHz (802.11b/g/n/ax): This band offers a limited number of channels (typically 11-14, depending on region), each 20 MHz wide. Due to spectral overlap, only channels 1, 6, and 11 are considered non-overlapping in North America. This severely limits channel reuse in dense deployments, making it susceptible to co-channel interference.
■ 5 GHz (802.11a/n/ac/ax): This band provides significantly more non-overlapping channels (e.g., around 25-30 depending on regulatory domain), each 20 MHz wide. This allows for much denser AP deployments with less interference. It also supports wider channels (40 MHz, 80 MHz, 160 MHz) by bonding multiple 20 MHz channels together to achieve higher data rates.
■ 6 GHz (802.11ax/Wi-Fi 6E, 802.11be/Wi-Fi 7): This band (also known as U-NII-5 to U-NII-8) offers an even greater number of wide, non-overlapping channels, providing substantial capacity for future Wi-Fi deployments and reducing congestion.