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

4.11 Automatic link maintenance.

Automated HF systems that implement automatic link maintenance (ALM) shall monitor link quality after link establishment and negotiate changes in operating frequency and power as described in 5.11. Changes in data rate and interleaver shall be negotiated by the HFDLP as described in FED-STD-1052.

4.11.1 Link quality monitoring.

Quality of an established link shall be monitored by the subsystem using the link and reported to the link maintenance controller. Alternate channels shall be evaluated using transmissions on unused traffic channels in the unused direction while a link is in progress.

4.11.2 Frequency negotiation.

When a link is in use for voice traffic, a single third-generation ALE (see 4.12) Response PDU containing a Preferred Channel command shall be sent at the end of each transmission and after every 10 seconds of uninterrupted voice transmission. The HFDLP Automatic Link Maintenance protocol shall be used to negotiate alternate frequencies when HFDLP is in use (see 5.11).

If either station detects imminent link failure, it shall initiate a frequency change using either the HFDLP, when it is in use, or by sending a repeated third-generation ALE Commence Traffic PDU that names the new channel. When the stations have completed a three-way handshake containing Commence Traffic or the equivalent HFDLP commands, they shall change to the new frequencies.

If the link fails without negotiation of a frequency change, the system that detects the failure shall automatically initiate link establishment on the most recently named alternate channel from the other station.

4.11.3 Automatic power control.

Third-generation ALE systems shall automatically adjust transmitter power in response to power control commands sent in the unused link direction on the associated calling channel.

4.12 Advanced automatic link establishment.

Advanced automatic link establishment, also known as third-generation automatic link establishment (ALE), provides functionality similar to second-generation ALE as described in MIL-STD-188-141 Appendix A, but with improved ability to link in stressed channels, to link more quickly, and to operate efficiently in large, data-oriented networks. Third- generation ALE is optional, but if implemented shall comply with MIL-STD-188-141, Appendix C, Third Generation HF Automation..

4.13 System parameters by address.

Not yet standardized. (This optional feature will extend the station table to include recommended antennas, antenna azimuths, frequencies, modems, and coding for use in communicating with each listed station.)