IBSS (Independent Basic Service Set)

An infrastructure mode wireless network basic service set (BSS) consists of one redistribution point — typically an access point (WAP or AP) — together with one or more “client” stations that are associated with (i.e. connected to) that redistribution point. The operating parameters of the infrastructure-BSS are defined by the redistribution point. Stations communicate only with the redistribution point that they are associated with, and all traffic within the infrastructure-BSS is routed through/bridged by that redistribution point.

Each basic service set has its own unique identifier, a BSSID, which is a unique 48-bit identifier that follows MAC address conventions. An infrastructure-BSSID is usually non-configurable, in which case it is either preset during manufacture, or mathematically derived from a preset value such as a serial number, the MAC address of the LAN connection, etc. As with the MAC addresses used for Ethernet devices, infrastructure-BSSIDs are a combination of a 24-bit Organization Unique Identifier (OUI, the manufacturer’s identity) and a 24-bit serial number. A BSSID with a value of all 1s is used to indicate the wildcard BSSID, usable only during probe requests or for communications that take place outside the context of a BSS.

From the point of view of a wireless clients, IEEE 802.11s wireless mesh networks appear as a conventional infrastructure mode topology, and are centrally configured as such. The formation of the mesh’s BSS, as well as wireless traffic management (including path selection and forwarding) is negotiated between the nodes (redistribution points) of the mesh infrastructure. The mesh’s BSS is distinct from the networks (which may also be wireless) used by a mesh’s redistribution points to communicate with one another.

In contrast to the stations in an infrastructure-mode network, the stations in a wireless ad hoc network communicate directly with one another, i.e. without a dependence on a distribution point to relay traffic between them. In this form of peer-to-peer wireless networking, the peers form an independent basic service set (IBSS). Some of the responsibilities of a distribution point — such as defining network parameters and other “beaconing” functions — are established by the first station in an ad-hoc network. But that station does not relay traffic between the other stations; instead, the peers communicate directly with one another. Like infrastructure-BSSs, independent-BSSs also have a 48-bit MAC address-like identifier. But unlike infrastructure-BSS identifiers, independent-BSSs identifiers are not necessarily unique: the individual/group bit of the address is always set to 0 (individual), the universal/local bit of the address is always set to 1 (local), and the remaining 46 bits are randomly generated.

A basic service set should not to be confused with the coverage of an access point, known as the ‘basic service area’ (BSA).

Related Articles