Afar AR-24010E, Operator'S Manual

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pulsAR radio Operator's Manual
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Codepoint Unused
When the codepoint field has the value xxx000 , the three most significant bits are interpreted as
precedence bits. The radio gives high priority to packets with a precedence field of 6 or 7. In
hexadecimal notation this translates into TOS values of E0 and C0.
 Low-priority: All other packets
When the time to transmit over RF arrives, the software always takes packets from the higher priority
queues first.
2.6 Encryption
The radios have the capability of encrypting the payload data transmitted over the air. You can select
the encryption algorithm between DES, Triple-DES, AES-128, and AES-256, and enter a unique key
to encrypt and decrypt the data. Refer to the encryption command in section 4.4 for complete details.
Turning encryption on has the following impact on the link performance:
1. Increase in the packet size. Block encryption algorithms require the packet length to be a
multiple of 8 bytes for DES or Triple-DES, 16 bytes for AES-128, and 32 bytes for AES-256.
The radio uses one of those additional bytes to control the truncation of the padded field on the
receive side, so there is always at least one added byte. For very long packets this padding may
be negligible, but for short packets it can add significant overhead. A worst case scenario would
be an ethernet packet of 64 bytes which, with AES-128 encryption will be padded to 80 bytes,
and with AES-256 to 96 bytes.
2. Increase in latency. There is a small delay introduced by the additional processing to encrypt and
decrypt data packets. The e decrypt time for a 100 byte packet is 0.28 ms, for a 1,000
byte packet is 0.62 ms irrespective of the algorithm. In addition to this added processing time,
the increased packet size referred above also impact latency, depending on how many bytes were
added to the packet and the RF transmit speed.
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