STANAG-4285 & HMTP-66 (HF Mail Transport Protocol) example

Other than (H)BFTP and CFTP, e-mails can be sent over HF using the protocol HMTP (HF Mail Transport Protocol) defined in STANAG-5066 Annex F and  MIL 188-141B Appendix E.  The HMTP protocol is used by a mail client to submit a mail-object to a mail server using the allowed HF transport waveforms, or alternatively, it may be used as the protocol to transfer a mail object over the HF subnetwork from one mail server to another. The HMTP protocol is NOT used to send and receive Formal or High Grade Military Messages but rather for informal interpersonal e-mail only.

The transmission has been heard on 5054.0 KHz/USB at 0804 UTC on 26 September, the used HF waveform is STANAG-4285: ACF and frame structure are shown in fig. 1. 

fig. 1 - ACF and frame structure of the head signal (STANAG-4285)

 

A 1776 bit period, often met in STANAG-5066, pops up after removal the STANAG-4285 overhead (fig. 2)

 

fig. 2 - 1776 bit period

 

The "payload" (email message) is visible in figure 3 once removed the STANAG-5066 headers:

fig. 3 - HMTP mail message

Since the data link protocol used in this transmission is STANAG-5066 we expect HMTP-66 sequences, and this is pecisely what you get (fig. 5):

fig. 5

 

Note that the sequences in-air are "splitted" in PDUs so we see sequences in seven files that will be re-assembled at S-5066 receive peer.