Érdekes, a szabvány szerint nem ugyanaz... :/
3.53 extended service area (ESA): The area within which members of an extended service set (ESS) may
communicate. An ESA is larger than or equal to a basic service area (BSA) and may involve several basic
service sets (BSSs) in overlapping, disjointed, or both configurations.
3.54 extended service set (ESS): A set of one or more interconnected basic service sets (BSSs) that appears
as a single BSS to the logical link control (LLC) layer at any station (STA) associated with one of those
BSSs.
3.137 station service (SS): The set of services that support transport of medium access control (MAC)
service data units (MSDUs) between stations (STAs) within a basic service set (BSS).
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5.2.3.1 Extended service set (ESS): The large coverage network
The DS and 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 BSSs
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.
Nothing is assumed by IEEE Std 802.11 about the relative physical locations of the BSSs in Figure 5-3.
All of the following are possible:
a) The BSSs may 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 may be physically collocated. This may be done to provide redundancy.
d) One (or more) IBSS or ESS networks may be physically present in the same space as one (or more)
ESS networks. This may arise for a number of reasons. Some examples are when an ad hoc 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.