26 February 2016

A real example of e-mail over HF (via FTP) using STANAG-5066 and MS188-110A

in this recording two stations run STANAG-5066 with BFTP protocol client (a File Transfer Protocol) in order to exchange e-mails using the MS188-110A serial waveform. Note that the E-mail delivery does not happen here using STANAG-5066 HMTP client but rather by FTP_ing the email file (containing all the SMTP headers and fields) ready to be processed by common e-mail clients such as Microsoft Outlook. 
It is worth mentioning that BFTP (Basic File Transfer Protocol) client is defined by  STANAG-5066 Annex F.10.2.2, that same Annex also defines the Compressed File Transfer Protocol client (CFTP) that provides the most bandwidth-efficient exchange of data just using BFTP to send compressed file (see the comment about "MIL-STD-188-141B Notice 1" below at the end of the post).
Talk about e-mail and file-transport protocols go beyond the purpose of the blog so I prefer to have an  HF approach, keeping in mind that STANAG-5066 is designed for running IP applications over HF (STANAG-5066 IP based networks can be thought of as being an HF radio based version of the Internet) and that the stuff, in this sample, is arranged as in pic. 1.

As said above, the heard waveform is a standard MS-188-110A serial, as can be verified by SA (pic. 2) although a little shift of the sub-carrier from the nominal 1800 Hz. Since at this stage the signal is coming directly from the USB demodulator, we face Over The Air (OTA) symbols. The structure of the MS188-110 frame is recognizable from the bitstream returned by the SA phase-plane demodulator after its conversion (pic. 3).

pic.3 - OTA bitstream after demodulation performed by SA
In order to dig the signal we need de-scramble and de-interleave it and then  remove the extra bits added by the FEC encoder: a basic decoder will do the job returning the bitstream after the MS188-110 removal (pic. 4). 

pic.4 - the bitstream after the MS188-110 removal
Once detected the presence of STANAG-5066 as "secondary" protocol, we need to remove also its encapsulation so to get  the email message that have been transferred by BFTP protocol at sender side. Note that the name of FTP protocol is HBFTP, as it appears in the output window of the analyzer (pic.5). 

pic.5 - the bits trasferred by HBFTP after removed STANAG-5066 and MS188-110A
The acronym HBFTP could stand for HF-BFTP and is suggested to be the Harris implementation of this protocol, available in mail-gateway as the HARRIS RF-6760W Wireless Message Terminal or RF-6750W Wireless Gateway.
The contents of 000_HBFTP--3  can be saved to a file and Windows assigns the .eml extesion since the file exhibits all the features as it was received from a conventional SMTP server via an Internet connection (pic.6).  The file can be  opened and processed by Microsoft Outlook w/out problems: Outlook simply does not care where and how this file has arrived (pic. 7). For reasons of confidentiality the email addresses have been deliberately blackened.


MIL-STD-188-141B (change notice 1, Appendix E) defines a version of email specially adapted to HF communications. Commands to and from the server are aggregated into blocks to overcome the high latency introduced by HF transmission methods. This greatly improves the efficiency of email when carried over HF.
E.5.2.1 Compressed file transfer protocol.
The Compressed File Transfer Protocol (CFTP) sends compressed e-mail over an HF link using a file transfer protocol, rather than a mail transfer protocol. Messages produced by an email application are processed by a MTA, compressed in CFTP, segmented in the STANAG 5066 Basic File Transfer Protocol (BFTP), and passed to the subnet interface by the STANAG 5066 Reliable Connection Oriented Protocol (RCOP). At the receiving node, this process is reversed, and the uncompressed e-mail message is delivered to the receiving MTA for delivery or forwarding.
At this purpose, it is worth noting that the name of the compressed file (.gz extension) produced by CFTP is visible in the non-sense output of the MS188-110A decoder  shown in pic. 8

The document "MIL-STD-188-141B Notice 1" can be downloaded from everyspec.com

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