Extended service set (ESS): The large coverage network

 Extended service set (ESS): The large coverage network

The DS and infrastructure BSSs allow IEEE Std 802.11 to create a wireless network of arbitrary size and
complexity. IEEE Std 802.11 refers to this type of network as the ESS network. An ESS is the union of the
infrastructure BSSs with the same SSID connected by a DS. The ESS does not include the DS.
The key concept is that the ESS network appears the same to an LLC layer as an IBSS network. STAs within
an ESS may communicate and mobile STAs may move from one BSS to another (within the same ESS)
transparently to LLC.
Owing to its distributed nature, a mesh BSS (MBSS) has no central entity like the AP of an infrastructure
BSS. Instead, an MBSS forms a single set of independent mesh STAs. This set is indivisible and cannot be

further unified. The ESS concept does not apply to the MBSS. However, it is possible to use a Mesh BSS as all or part of the DS that connects an ESS.


All of the following are possible
a) The BSSs partially overlap. This is commonly used to arrange contiguous coverage within a
physical volume.
b) The BSSs could be physically disjoint. Logically there is no limit to the distance between BSSs.
c) The BSSs are physically collocated. This could be done to provide redundancy.
d) One (or more) IBSS or ESS networks are physically present in the same location as one (or more)
ESS networks. This could arise for a number of reasons. Some examples are when an IBSS network
is operating in a location that also has an ESS network, when physically overlapping IEEE 802.11
networks have been set up by different organizations, and when two or more different access and
security policies are needed in the same location.