Symbol Technologies Spectrum24 AP-4131 - Manual (Page 35)

Introduction
AP-4131 Access Point Product Reference Guide 25
A TIM is a compressed virtual bitmap identifying the AP associated MUs in
PSP mode that have buffered directed messages. MUs issue a poll request
when APs issue a TIM. A beacon with the broadcast-indicator bit set causes
the MU to note DTIM Count field value. The value informs the MU of the
beacons remaining before next DTIM. This ensures the MU turns on the
receiver for the DTIM and the following BC/MC packet transmissions.
1.3.9 Data Encryption
Any wireless LAN device (including Spectrum24 devices operating on a
wireless network) faces possible information theft. Theft occurs when an
unauthorized user eavesdrops to obtain information illegally. The absence of
a physical connection makes wireless links particularly vulnerable to this form
of theft.
Encryption becomes the most efficient method in preventing information
theft and improving data security. Encryption entails scrambling and coding
information, typically with mathematical formulas called algorithms, before
the information is transmitted. An algorithm is a set of instructions or formula
for scrambling the data. A key is the specific code used by the algorithm to
encrypt or decrypt the data. Decryption is the decoding and unscrambling of
received encrypted data.
The same device, host computer or front-end processor, usually performs
both encryption and decryption. The data transmit or receive direction
determines whether the encryption or decryption function is performed.
The device takes plain text, encrypts or scrambles the text typically by
mathematically combining the key with the plain text as instructed by the
algorithm, then transmits the data over the network. At the receiving end
another device takes the encrypted text and decrypts, or unscrambles, the
text revealing the original message. An unauthorized user can know the
algorithm, but cannot interpret the encrypted data without the appropriate
key. Only the sender and receiver of the transmitted data know the key.
Symbol uses the Wired Equivalent Privacy (WEP) algorithm, specified in
IEEE 802.11 section 8, for encryption and decryption. WEP uses the same
key for both encrypting and decrypting text. Typically an external key service
distributes the key. Users should change the key often for added security.