E-DOC-CTC-20060609-0001 v2.0
Chapter 1
Introducing Wireless Networking
7
Basic Service Set Identifier (BSSID)
The Basic Service Set Identifier (BSSID) uniquely identifies each BSS. The BSSID is a 48-bit address with the
same format as an IEEE 802 MAC address. The value of all 1s is used to indicate the broadcast BSSID.
The station that starts the BSS determines the BSSID of that BSS, depending on the topology:
> In case of an ad-hoc network, the BSSID is determined by the use of a 46-bit random number generator.
The used mechanism provides a high probability of selecting a unique BSSID.
> In case of an infrastructure network, the BSSID is the same as the MAC address of the AP. All wireless
stations communicating to the AP send to the BSSID.
Service Set Identifier (SSID) or Network Name
Wireless stations communicate with each other through the air, which is a shared medium. As no physical
connection exists between the APs and the wireless stations, a name must be given to allow unique
identification of your WLAN. This is called the Service Set Identifier (SSID) or Network Name. Wireless
stations must be part of a specific SSID environment in order to communicate with the other stations
belonging to the same WLAN.
The SSID has a length between 0 and 32 octets. A length equal to 0 octets indicates the broadcast SSID. This
SSID is included in the SSID Information Element (IE), which is part of management frames such as beacon
frames, probe request/response frames and association/reassociation request frames. The following
illustration depicts the format of the SSID IE:
Two types of SSIDs are defined, depending on the topology:
> In case of an ad-hoc network, the SSID is also called the Independent Basic Service Set Identifier (IBSS
ID).
> In case of an infrastructure network, the term Basic Service Set Identifier (BSS ID) or Extended Service
Set Identifier (ESS ID) can be used instead of SSID.
The following example illustrates the use of the BSSID and SSID:
i
In many cases both types of SSID are referred to as SSID or Network Name.
!
The use of the term Basic Service Set Identifier can cause confusion with the BSSID defined as the
MAC address of the AP.
Element
ID
1 byte 1 byte 0-32 bytes
Length SSID
Distribution System
BSS2
ESS
BSS1
BSSID1
BSSID2
SSID
SSID
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