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NP6800 - Wireless LAN Access Point Page 35
Advanced Topics
Network Topology
The IEEE 802.11 standard supports three basic topologies for WLANs - the Independent Basic
Service Set (IBSS), the Basic Service Set (BSS), and the Extended Service Set (ESS). WLAN
components can be used to extend, enhance or entirely replace existing Ethernet infrastructure.
The NetComm NP6800 - Wireless LAN Access Point can accommodate any of these WLAN
topologies.
IBSS
An Independent Basic Service Set or Ad Hoc network consists of two or more wireless stations
that communicate directly, peer-to-peer, without the services of a wireless access point. An
example of an Ad Hoc or IBSS network would be a group of wireless-equipped laptop
computers at a trade show set up to share information. In this arrangement, one of the WLAN
units is elected to act as a controller or base station, similar to the function of a wireless access
point except there is no connection to a wired Ethernet LAN.
BSS
In a Basic Service Set network, a wireless access point performs multiple tasks - it is a base
station and a network access controller for the wireless stations in the WLAN. The access point
can also provide a connection to a wired Ethernet LAN for the BSS member stations. An
example of a BSS might be a business meeting conducted in a room with only a single Ethernet
port available. Each participant has a wireless laptop computer and requires simultaneous access
to a data server on the Ethernet LAN. A wireless access point provides the connection to the
Ethernet LAN and acts as the network control station for the BSS network members.
In a BSS network, the wireless access point performs functions similar to an Ethernet switch.
The access point controls network access and maintains a dynamically updated list of all the
members of the BSS. Wireless stations in the BSS are identified by their MAC Addresses.
ESS
An Extended Service Set is a series of two or more basic service sets (BSSs) networked on an
Ethernet LAN. Each access point provides connections to the Ethernet LAN for their respective
BSS members. Each BSS member is identified by a unique number, the BSSID (actually the
MAC address of the access point). Wireless stations (such as a laptop computer with a
NetComm NP7032 - Wireless LAN PC Card installed) on an ESS network automatically select
the access point or BSS that can serve them best (has the best signal). If no access point can be
found, the device will scan for a usable access point.
An ESS network can be set up so that wireless stations can roam anywhere within the range of
the access points and still maintain links to both the WLAN and the Ethernet LAN. In this case,
each station shares a common ESS. The ESS network is identified by an ESSID that is known
and used by all of the stations in the ESS network.
Wireless access points can also be used to segment a wireless network. Under such
circumstances, more than one ESS might be used. Two or more separate ESS's can occupy the
same physical space. Each station on a WLAN can use only one ESS - and thus only one ESSID.