Interaction of architectural elements

An essential functional feature of ESS is the dynamism of changing its subscriber structure: network subscribers can connect to it at any time, interrupt communication with the network (leave it), mix between different BSS networks. The dynamic functioning of the ESS is provided by the interaction between the elements (components) of its architecture.

The set of functions performed by the elements is called the corresponding services . The standard defines 9 types of services: what is wlan network

- subscriber authentication;

- subscriber associations;

- deauthentication of subscribers;

- disassociation of subscribers;

- reassociation of subscribers;

- wired LAN integration;

- message delivery;

- confidentiality of messages;

- distribution of messages.

Services are classified according to two main criteria:

1) based on the role of services in ensuring the functioning of the network (according to this feature, services are distinguished that ensure the formation of a network, and services that ensure the transfer of messages between subscribers);

2) by the type of network elements that perform the corresponding service function. On this basis, services are divided into station (Station Service - SS) and distribution system services (Distribution System Service - DSS).

The formation of a network, provided that all its infrastructural elements (distribution systems, access points, portals) are available, consists in connecting / disconnecting its mobile subscribers. The connection of the latter involves checking their authenticity (Authentication) and association (Association) of subscribers in the network. When mobile subscribers leave the network, their disassociation and deauthentication are carried out. The movement of mobile subscribers from one BSS to another without leaving the ESS is provided by the Reassociation service . Authentication / de-authentication are station services and association / disassociation are distribution system services. The logical connection to the DS of the wired LAN is provided by the integration service included in the DSS.

The transmission of messages between subscribers within the network is carried out by delivery services (MSDU delivery), privacy (Privacy) and distribution (Distribution) messages. The first two are station-based, the last one is a DSS service. Information exchange between network elements in the process of its formation and operation involves the transfer of messages of two types: service messages, which provide management (Management) and control (Control) access to the wireless medium, and data transmission messages (Data). Messages are transmitted in the form of frames (Frame), the list of varieties of which is regulated by the standard.

In the process of connecting / disconnecting and functioning in the network, mobile stations can be in one of the following three states:

- state 1 - initial state when STA is not authenticated and not associated;

- state 2 - intermediate state (during connection / disconnection), when STA is authenticated, but not associated;

- state 3 - operational functional state when STA is authenticated and associated.

The state number defines the list of frame subtypes that can be used in this state; the narrowest list corresponds to state 1, the full list corresponds to state 3. Depending on the state number, starting from which it is allowed to use frames of various types and subtypes, there are 3 classes of frames:

- class 1, which includes frames used from state 1;

- class 2, which includes frames used from state 2; - class 3, which includes frames used only in state 3.

Let's note the qualitative differences between frames:

1) Class 1 frames provide the execution of procedures related to STA connection to the network, STA access to the wireless environment (Wireless Medium, WM) and data transfer, but the possibility of using DS is excluded for all procedures;

2) Class 2 frames ensure the execution of management procedures associated with STA association, disassociation and reassociation; reassociation of STA is possible only if it was previously associated;

3) class 3 frames provide data transmission using DS (this is their essential difference from class 1 data frames).