MIL-STD-187-721 Interoperability And Performance Standard For Advanced Adaptive Hf RadioThe purpose of this document is to describe the technical parameters for adaptive high frequency HF radio that are more advanced than those described in MIL-STD-188-141. The advanced technology contained in this standard will guide the planning of military adaptive HF radio network technology into the 21st century. To fully understand and utilize this document, it is necessary to refer to portions of MIL-STD-188-141.

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MIL-STD-187-721D

5.11.2  Data frame CMDs for link maintenance.

ALM CMDs shall be embedded in a data frame of an HFDLP data series by setting the Reserved bit to 1 in the Reverse Channel Control Frame Recommendation of a Data Frame header.  The ALM CMD shall be left-justified in the first seven bytes of the data frame as shown on figure 29. The remaining bits of the data frame shall be set to 0.

2               6                                                                                      42                                                                                           6

byte 0                      byte 1                     byte 2                       byte 3                        byte 4                     byte 5                byte 6

FIGURE 29.  HFDLP ALM CMD embedding in data frame.

The CMDs sent in HFDLP data frames shall be identical to those sent in control frames.

5.11.3  Initiation of ALM operation.

Before HFDLP terminals begin ALM operation, they shall ascertain that both are ALM capable. If an ALM CMD has not been received from the other terminal, no ALM CMD other than a No Op shall be sent.  The response to an ALM No Op may be any ALM CMD, including a No Op.

5.11.4  Alternate frequency negotiation.

After ALM operation has been established (see 5.11.3), the best alternate frequency (or frequencies) for transmissions to a station shall be reported in every HFDLP data series and in every data ACK that is not used for another ALM CMD.  These alternate frequencies should be provided to the ALE controller for guidance in reestablishing the link should it fail, and for future use for link establishment.

If either terminal detects imminent link failure, it shall initiate a frequency change by sending a Change Frequency CMD at the first opportunity.  The other terminal shall respond with a Change Frequency CMD indicating its preferred new frequency.  If the first terminal receives this

response, it shall acknowledge the frequency change by repeating its Change Frequency CMD and shall depart to the new frequency.  Upon receipt of the acknowledgment (or the expiration of a timeout awaiting the acknowledgment), the second terminal shall also depart to the new

frequency.  The second terminal shall initiate HFDLP link establishment.

5.11.5  Automatic power control.

HFDLP ALM Adjust Power CMDs may be sent after the HFDLP terminals have negotiated ALM

operation as described above.  When an Adjust Power CMD is received, the terminal shall pass the request to the station device that can implement the power change.

5.12  Advanced third-generation automatic link establishment. See MIL-STD-188-141.

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