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Re: HF Radio Email

Thanks for the information.  This looks like something we will keep 
an eye on.

At present we are using e-smith linux, qmail, and a Codan 
radio/modem and some patches for dip written by MAF.  This allows 
remote users to dial in from a simular setup on the field, except 
using regular win9x dial up networking and a stock email client to 
send and recieve emails.  Where there is good reception this is a 
pretty good system, but in poorer reception areas TCP/IP does not 
seem to be the answer because of the overhead involved.  

We are looking at UUCP, and other alternatives, but it needs to be 
pretty transparent on the users end, be simple, and work.  Most of 
the people on the client side are not by and large, power users.   The 
machines in the field are various flavors of windows with no real 
desire on anyone's part to switch to linux on the remote ends at this 
time.  This may come in the future.

Thanks again

RRP

On 23 Mar 2002, at 22:55, Arnau Sanchez wrote:

> Hello,
> 
> Perhaps this is not the appropriate place to speak deeply about it.
> However some comments here may be useful for all and us:
> 
> ----
> 
> We are precisely working in this subject, an email system for HF links.
> We use sound cards as modems for conventional voice HF radios, so the
> system will be cheap.  The system is designed for subnets with a server
> and several clients. We have not yet performed tests on real channels
> but we think we could achieve between 1000 and 2000 bps, of real
> user-data.
> 
> We are now using the following protocol/application structure:
> 
> Postfix: As MTA for ruting messages trough a BSMTP transport.
>        Probably any other MTA can be used.
> 
> Bsmtpd: Batched SMTP transport. It packs messages in compressed batches.
> 
> Uucp: Unix-to-Unix Copy. This level sends the mails compressed by bsmtp.
>       The batching is performed in the moment of a successfull uucp
>       connection. We are using the 'y' protocol because it is suitable
>       for half-duplex and error-free links (the channel is NOT
>       error-free, but that's ax25's duty).
> 
> AX25: This protocol is used to reliably transfer uucp y packets and
> provaides 
>       medium access control. The standard Linux AX-25 implementation was
>       modified the have better throughput.  The most important is the
>       implementation of an efficient selective reject system (SREJ).
>       Just lost packets are resent (some changes in timeout's
>       implementation has been mandatory). A DAMA-Master (for the server)
>       has been also programmed (with new specifications, does not
>       follows traditional DAMA). This improves efficiency when two or
>       more clients want, at the same time, to communicate with the
>       server.
> 
> Soundmodem: This package from Thomas Sailer allows to use as modem any
> sound card
>       supported by linux's kernel. Then, input/output jacks from the
>       sound card go directly to the radio. A PTT circuit is needed:
>       (http://www.baycom.org/~tom/pcf/ptt_circ/ptt.html). Soundmodem has
>       several different modulations (AFSK, FSK, PSK, ...). The best for
>       HF is "newqpsk".
> 
> Newqpsk: This module was developed by Pawel Jolocha (SP9VRC) for the
> DSP560002.
>       Fortunately, Tomi Manninen did a great job translating it from
>       DSP's assembler to C, so now it can be used in Linux. We think
>       newqpsk still needs some improvement (anyone interested?), but
>       with the exception of bad links, it is a good option.
> 
> Moreover, inside Newqpsk, strongest Forward Error Correction was added
>       (FEC), based on convolutional Turbo Codes (a good tutorial:
>       http://www.ece.arizona.edu/~ryan/turbo2c.pdf). The TC
>       implementation that I am using was made in 1998 by Mathys Walma
>       and I have made some little improvements: puncturing system to
>       allow variable rate, and a crc tail to allow faster decoding.
>       (There is one problem here, We have tried to contact M. Walma but
>       his mail is not active, so we cannot guarantee he allows his code
>       to be released under GNU license).
> 
>       Although it may be more than one client, with DAMA, we can assure
>       that only one is active at a time. This allows to make
>       Point-to-Point communications and adaptative FEC (redundancy, 
>       thus speed, is changed depending on the current link quality).
> 
> We think that in less than two months we well have all of this stuff
> working and better documented, but we are sure that the "newqpsk" could
> be improved, so anyone with knowledge in signal processing is welcome.
> 
> ps: For people who know spanish we have a working document with a more
> detailed
>     description here:
> 
>     http://www.ehas.org/trabajo/hf/HFModem.doc
> 
>     This document is by no means complete, so people who wants to use
>     the entire system might need some help (in fact the interface
>     between UUCP and AX25 levels needs some simple but specific
>     programs: uucall, ...).
> 
> On 09 de march 2002, Randy and Wanda Potratz & Family wrote:
> 
> > Has any one on this list ever tried to set up and run a HF radio email
> > system?  I have some questions on configuration for such a project
> > here in Niger, West Africa.
> 
> -- 
> 
> Arnau Sanchez Sala 
> arnau@gbt.tfo.upm.es
> 
> Joaquin Seoane Pascual
> joaquin@dit.upm.es
> 
> Visit http://www.ehas.org for a background of our work
> (unfortunately only in spanish).
> 
> 
> 
> 
> -- 
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> 


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