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

LQA CMD) is determined by the order of addresses in the acknowledgment.  Non-responding stations may be omitted from both the leading call and message section of the acknowledgment.

5.4.3.3  Two station - multiple channel polling.

a.  A technique commonly called "poll before linking" evaluates several channels immediately before linking to select the current best channel.  This may be performed using an individual poll on each channel, but a significant amount of time is wasted in unnecessary scanning calls. For example, evaluating 10 channels takes about 150 seconds, with over half of this time consumed by calling cycles of scanning calls.  All but the first scanning call may be eliminated if the stations involved agree upon a list of channels to be evaluated, and then step through this list synchronously.

b.  When stations with identical scan sets want to evaluate all channels in their common scan set, the following protocol is used:

(1)  The caller embeds CMD <LQA request> CMD <channel scan request> in the call.  (A

channel scan request carries as a parameter the sender's tune time, as shown on figure 5).

(2)  The responder shall respond to the LQA request (requirement of MIL-STD-188-141). If the response contains CMD <channel scan request>, the requested channel scan has

been accepted, and both stations are obligated to complete it.  Otherwise, an individual poll is completed on the current channel, and the protocol terminates.

(3)  When the response contains a channel scan request (along with an LQA report with the request bit set), an individual poll is completed on the initial channel.  The acknowledgment from the caller will contain an LQA report with the request bit negated.

(4)  Both stations proceed to the next channel, listen for activity, and tune.  After the longer of the two tune times in the channel scan request has elapsed, the caller initiates a non-scanning individual poll: a leading call, an LQA request, and the caller's frame termination.  The response will contain an LQA report with the request bit set, and the acknowledgment from the caller will contain an LQA report with the request bit negated.

FIGURE 5.  Channel scan request CMD format.

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