To move between access points
within an ESS, the roaming station sends a reassociation request to the new access point in
order to seamlessly join the new BSS and leave the old one. Any station can terminate an
association by sending a disassociation notice.
2.2.4.4 Confidentiality
Confidentiality is achieved by protecting transmitted information with encryption. The
standards offer several options for encryption, each of which is a part of a larger security
policy. APs (and their equivalent in an ad hoc network) advertise these security policies in
beacon and probe response packets. An AP can enforce security policies for all the nodes in
its BSS. Each node in an ad hoc network must enforce its own security policy. This topic is
covered in detail in the next section, Security.
2.2.5 Security
Secure communication is problematic in all radio networks. A wired network can be
secured at its edges - by restricting physical access and installing firewalls, for example. A
wireless network with the same measures in place is still vulnerable to eavesdropping.
Wireless networks require a more focused effort to maintain security.
This section presents a few basic concepts of communications security, then describes
the main generations of security enhancements to 802.
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