ProLinx 6202-WA-DFNT-DFCM3, Руководство пользователя

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Reference 6202-WA-DFNT-DFCM3 ♦ ProLinx Gateway
Wireless EtherNet/IP to DF1 Master/Slave-3 ports
ProSoft Technology, Inc. Page 107 of 190
February 2, 2009
Prior to communicating data, wireless clients and access points must establish a
relationship, or an association. Only after an association is established can the
two wireless stations exchange data. In infrastructure mode, the clients associate
with an access point. The association process is a two step process involving
three states:
1 Unauthenticated and unassociated,
2 Authenticated and unassociated, and
3 Authenticated and associated.
To transition between the states, the communicating parties exchange messages
called management frames.
We will walk through the process of a wireless client finding and associating with
an access point.
1 All access points transmit a beacon management frame at fixed interval. To
associate with an access point and join a BSS, a client listens for beacon
messages to identify the access points within range. The client then selects
the BSS to join in a vendor independent manner.
2 All of the network names (or service set identifiers (SSID)) which are usually
contained in the beacon frame are presented to the user so that they may
select the network to join.
3 A client may also send a probe request management frame to find an access
point affiliated with a desired SSID.
4 After identifying an access point, the client and the access point perform a
mutual authentication by exchanging several management frames as part of
the process. The two standardized authentication mechanisms are described
below.
5 After successful authentication, the client moves into the second state,
authenticated and unassociated.
6 Moving from the second state to the third and final state, authenticated and
associated, involves the client sending an association request frame, and the
access point responding with an association response frame. After following
these steps the client becomes a peer on the wireless network, and can
transmit data frames on the network.
Open System Authentication
Open system authentication is the default authentication protocol for 802.11. As
the name implies, open system authentication authenticates anyone who
requests authentication. Essentially, it provides a NULL authentication process.
Experimentation has shown that stations do perform a mutual authentication
using this method when joining a network, and our experiments show that the
authentication management frames are sent in the clear even when WEP is
enabled.