Elements of the WLAN architecture

The list of core elements includes basic service kits, portals, and a distribution system. The structure and content of the functions performed by the listed elements is as follows.

1. Basic Service Sets (BSS) are wireless LAN components that allow their nodes to communicate with each other and with other LAN nodes by transmitting signals using electromagnetic waves. The structural constituent parts of the BSS are stations (Station - STA) and access points (Access Point - AP).

BSSs are a collection of network nodes and wireless network adapters. A host is any device that is a source of packet messages (computer, digital telephone, etc.). WNIC provides reception and transmission of radio signals (PHY-layer), as well as the functions of a MAC-layer controller. In general, the term “station” in relation to a collection of a node and a WNIC corresponds to the analogous concept stipulated by the Radio Regulations - it is a collection of receivers and transmitters, including additional devices necessary to perform the functions of a radiocommunication service.

An access point (AP) is an entity with STA properties that performs two functions: coordinating the access of BSSs to the common wireless environment and access of BSSs to the distribution system.

The need to coordinate the work of BSS stations is due to their use of a common frequency-territorial resource. The area within which communication between BSSs is provided is called the Basic Service Area (BSA). The weight of BSSs shares one common frequency band for radio signal exchange, and collisions between radio signals of different stations result in harmful mutual interference, which precludes the possibility of simultaneous communication of several stations. Communication between BSS stations is carried out in half-duplex mode with signal relay (similar to radio relay communication) of different STA access points. The set of functions performed by the STA and AP to ensure the transmission of messages within the BSS is called the Station Service (SS).

Access points are the infrastructure elements of the BSS; they are used in all premises (basic service areas) that are designed for continuous WLAN operation (in particular hot spots). As infrastructure elements, APs provide an interface between the BSS and the LAN distribution system. In case the BSS is autonomous, the access point can provide direct access to the backbone network (Internet). For this purpose, industrial designs of AP are equipped with a router.

2. A Distribution System (DS) is a network element that transfers messages between different BSSs, as well as between the BSS and the wired LANs in the network. The medium that allows messaging between network segments (wired and wireless) is called Distribution System Medium (DSM). The set of functions performed by DS is referred to as the distribution system service. (Distribution System Service - DSS). Station Services (SS) and DSS together provide the ability to transfer messages between STAs belonging to different LAN segments. An essential feature of message transmission via DS is that the transmission protocols are MAC-layer protocols, so that stations of different BSSs and wire segments communicate with each other without going beyond this layer.

The digital network distribution system environment that is located inside buildings is generally wired. The distribution environment for LANs that span segments that are dispersed across an open facility (such as a campus or office) can be wireless. The IEEE 802.11 standard does not impose restrictions on how DSM is implemented, nor on the list of functions of the ISO / OSI protocol stack that an environment can perform. In particular, these functions can go beyond the 2nd (link) layer and cover the 3rd (network) layer. The latter corresponds to the interconnection of LAN with wide area networks (WAN), in particular, the Internet (in this case, a router). The creation of an interface between DS and WAN corresponds to one of the most common uses of Wi-Fi - WLAN - the creation of hotspots. Under the IEEE 802.11 protocol, the relationship between WLAN and WAN is not regulated.

3. Portals are network elements through which wired network segments are connected to the Distribution System (DS), operating in accordance with the requirements of wired LAN standards (for example, 802.3 - Ethernet). Through portals, messages are transmitted between wireless and wired network segments according to MAC-level protocols. Connecting wired segment nodes to DS using portals is called network integration . Due to the transfer of messages according to the protocols of the same layer (MAC-layer), the nodes of all network segments, wired and wireless, are logically equal.

The collection of all BSS networks and integrated wired segments (local area networks) is referred to as the Extended Service Set (ESS). The area occupied by ESS elements is referred to as the Extended Service Area (ESA). The maximum number of ESS nodes is not regulated by the IEEE 802.11 standard. ESS infrastructure: its distribution system, access points, portals, interface with the WAN - is created by the operator (provider) of the ESS. The network provides, firstly, the interconnection between all nodes included in the wired and wireless segments, and, secondly, the connection with the nodes of the global network (if such communication is provided).

The unambiguity of identification of network nodes during the transmission of messages between them is ensured by the adopted system of code designation of network elements. There are 3 types of element identifiers: wlan definition

- ESS identifier (Service Set Identifier - SSID), which is an ESS name, consisting of 32 alphanumeric characters;

- BSS identifier (Basic Service Set Identifier - BSSID), which matches the MAC address of the access point of the corresponding BSS;

- STA identifier , which coincides with the MAC address of the station under consideration.

The MAC addresses are assigned to the AP and STA in accordance with generally accepted rules: the first three bytes of the address are used to designate the NIC manufacturer, and the remaining three are used to designate the NIC number. Network identifiers (SSIDs) are defined by their operators and are usually a textual "network name". All ESS stations must have the right to use its telecommunication resources. SSIDs are used for the initial (initial) verification of the subscribers' eligibility to work in the ESS.