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6.0 Register/Command Reference
S158 FEC (Forward Error Correction) Mode
A number of FEC schemes are available with different coding rates.
FEC consumes significant bandwidth: depending on which coding rate is
chosen, a number of coding bits are transmitted along with the ‘data’ bits. In
‘noisy’ or long-range communications environments, FEC may effectively
increase throughput by decreasing the amount of packet retransmissions which
would otherwise be required.
Communications range may also be extended with the use of FEC: at a certain
distance where data would otherwise be unacceptably corrupted, employing
FEC may be all that is required to maintain the integrity of that data at that
distance.
If throughput is not of
primary concern and there
is an emphasis on
providing the most robust
data communications,
FEC should be
considered.
Values
0 No FEC
1 Hamming (7,4)
2 Hamming (15,11)
3 Hamming (31,24)
5 Binary BCH (47,36)
6 Golay (23,12,7)
7 Reed-Solomon (15,11)
Types of FEC available within the P900:
Hamming (7,4) : Information rate 0.5,
corrects 1 out of 7 bits
Hamming (15,11) : Information rate 0.66,
corrects 1 out of 15 bits
Hamming (31,24) : Information rate 0.75,
corrects 1 out of 31 bits
Binary BCH (47,36) : Information rate 0.75,
corrects 2 bits
Golay (23, 12, 7) : Information rate 0.5,
corrects 3 bits
Reed-Solomon (15,11) : Information rate 0.687,
corrects 2 nibbles
Values
S159 Encryption Mode (AES)
0 No encryption
1 AES 128 bit
2 AES 192 bit
3 AES 256 bit
AES encryption is only available in models delivered as –AES. This is a
factory configured option that can only be loaded and enabled at the
factory at time of assembly. The use of AES encryption, and export laws
governing AES, vary from country to country, contact Microhard Systems
Inc. for more information.
AES (Advanced Encryption Standard) provides an extremely strong level of
encryption for data for security of wireless data communication.
Up to three levels of AES are available, 128 bit, 192 bit and 256 bit. Only the specific options enabled by the factory
will be available Once a level of AES is chosen using register S159, the encryption key must be entered. The same
AES setting and encryption key must be entered on every modem in the network.
The size of the key is dependant of the level of AES:
128bit AES: 16 Byte Encryption Key
192bit AES: 24 Byte Encryption Key
256bit AES: 32 Byte Encryption Key
The encryption key can be entered in registers S107 or S177 as they share the same key array for encryption. S107
(Static Mask) is used to enter in up to 32 printable characters (ASCII). If using 128 or 192 bit AES, any character
entered after 16 or 24 bytes respectively will be ignored. If less than the required number of characters is entered, 0’s
will be appended to fill the encryption key array.
To improve the strength of the key, S177 can be used to enter 16-32 bytes (dependant of the AES type) of binary
non-printable characters. This register requires the appropriate number bytes to be entered. In other words, if you are
using AES256, S177 requires 32 bytes of data to be entered. A binary file can be transferred to the modem using a
terminal program after a ATS177= command has been invoked.
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