Siemens CP 1515 - Manual (Page 183)

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Industrial Ethernet Wireless LAN RLM Manager, CP 1515 Manager
C79000-G8976-C171-01
183
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It is best to create a single access control table and store it on the harddisk
of the LAN administrator station and/or share it with other LAN administrator
stations. You are advised to use only one table for all Radio Link Modules.
For more information refer to Creating/Editing an Access Control Table (page
161) .
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The WEP Encryption functionality allows the wireless system to support up
to four different keys simultaneously. This is in accordance with the 802.11
standard, which defines four so-called “default keys”
.
These keys can be used to smooth the transition from the usage of one key
to usage of a next key. The general requirement for two cards to transmit
encrypted between each other is that they share a common key value at the
same key-index number in the 4-key area at the moment of transmission.
The key-index of the key that was used for encryption is transmitted in clear-
text in the header of the message, and will be used at the receiving side to
determine which of the 4 keys to use for decryption.
It is not mandatory that both sides (typically RLM and SIMATIC NET
Industrial Wireless LAN station) have the same active set of 4 keys. As long
as there is one key in common, they can communicate, provided they both
use that common key.