IEEE 8011 Architecture and Services

In the year 1990, IEEE 802.11 Committee formed a new working group, the IEEE 802.11 standard which defines protocols for Wireless Local Area Networks (WLANs). Just like how Ethernet provides services for wired media, IEEE 802.11 architecture is designed to provide features for wireless networks.

An AP supports both wired and wireless connections. The 802.11 standard calls the upstream wired network the distribution system (DS). The AP bridges the wireless and wired L2 Ethernet frames, allowing traffic to flow from the wired to the wireless network and vice versa. Each wireless network has a unique SSID.

The 802.11 architecture provides some basic services for WLANs whose implementation is supported by MAC layer:

Basic Service Set

The Basic Service Set configuration consists of a group of stations and relies on an Access Point (AP), which serves as a logical hub. Stations from different BSSs interact through the AP, which functions as a bridge, linking multiple WLAN cells or channels.

Operating Modes

Depending upon the mode of operation, BSS can be categorized into the following types:

• Infrastructure BSS: Communication between stations takes place through access points. The AP and its associated wireless clients define the coverage area and form the BSS.

• Independent BSS – Supports mutual communication between wireless clients. An ad-hoc network is spontaneously created and does not support access to wired networks.

Independent Basic Service Set

In the IBSS configuration, also referred to as independent configuration or ad-hoc network, no single node is required to act as a server. The stations communicate directly with one another in a peer-to-peer basis. Generally, IBSS covers a limited area instead of a large network. Typically covering a specific area, IBSS is used for specific, short-term purposes with a limited number of nodes.

Extended Service Set

ESS connects multiple BSSs and consists of several BSS cells, which can be interlinked through wired or wireless backbones known as a distributed system. Multiple cells use the same channel to boost aggregate throughput to network. The equipment outside of the ESS, the ESS and all of its mobile stations comprise a single MAC layer network where all stations are virtually stationary. Thus, all stations within the ESS appear stationary from an outsider’s perspective.

Other components include:

• Distribution System (DS): Links APs within the ESS.
• Portal: Serves as a gateway to other networks.

• Roaming: In an environment with multiple access points (like a large office building or campus), a device can move from the range of one AP to another and still maintain its connection. This is possible due to the underlying architecture of the IEEE 802.11 standard which allows for roaming between APs.
• Authentication and Association: Before a station can send or receive data frames on a WLAN, it needs to establish its identity with an AP. This process is called authentication. After authentication, the station then establishes a data link-layer connection with the AP through a process called association.

The IEEE 802.11 standard, commonly known as Wi-Fi, outlines the architecture and defines the MAC and physical layer specifications for wireless LANs (WLANs). Wi-Fi uses high-frequency radio waves instead of cables for connecting the devices in LAN. Given the mobility of WLAN nodes, they can move unrestricted within the network coverage zone. The 802.11 structure is designed to accommodate mobile stations that participate actively in network decisions. Furthermore, it can seamlessly integrate with 2G, 3G, and 4G networks.

The Wi-Fi standard represents a set of wireless LAN standards developed by the Working Group of IEEE LAN/MAN standards committee (IEEE 802). The term 802.11x is also used to denote the set of standards. Various specifications and amendments include 802.11a, 802.11b, 802.11e, 802.11g, 802.11n etc.