802.11 Protocol Architecture
Because of the connection to a wired network, an ESS architecture
enables users to access a much wider range of services, such as web
browsing, email, and corporate servers. In addition, roaming between
access points is usually implemented by connecting each access point
to Ethernet.
The deployment of wireless LANs using access points is much more
common than Ad Hoc networks. As a result, this book focuses on
describing 802.11 functions as they relate to ESSs. When necessary,
however, this book describes variations corresponding to an IBSS.
Here we reiterate that the 802.11 standard refers to stations as either
access point (AP) stations or Non-AP stations and uses the word
“station” to refer to both. In this text we will refer to Non-AP stations
as client stations, mobile stations, or simply stations, such as laptops
using wireless PC cards for connectivity both to each other and to
access points.
System Services
The IEEE 802.11 architecture allows for the possibility that the DS
medium may not be identical to an existing wired LAN. A DS medium
may be created from many different technologies including current
IEEE 802 wired LANs. The 802.11 series of standards does not
constrain the DS medium to be either data link or network layer based,
nor do the 802.11 standards constrain a DS to be either centralized or
distributed in nature. IEEE 802.11 explicitly does not specify the
details of DS implementations. Instead, 802.11 specifies services. The
services are associated with different components of the architecture.
There are two categories of an IEEE 802.11 service - the station service
(SS) and the Distribution System Service (DSS). Both categories of
service are used by the 802.11 MAC sublayer.
The service provided by stations is known as the station service. The
SS is present in every 802.11 station (including access points, because
access points include station functionality). The SS is specified for use
by MAC sublayer entities. All conformant stations provide SS. The
station services are as follows:
Authentication
