File transfer protocol for Radio Links

What is the most suitable file transfer protocol when using HF,VHF
radio link with a digital modem.

I tried the Zmodem with crash recovery in MS Hyper Terminal to transfer
relatively small files but the transmission fails at the first bad
packet

But I should restart the transfer every time

I think that Zmodem is a full duplex protocol and digital radio modems
operates on a half duplex manner

So Zmodem times out waiting ....

Any advice or suggestion is welcomed

Essam Salah

 

[James Meyer]

On 17 Feb 2005 02:01:59 -0800, esamsalah@gmail.com wroth:

What is the most suitable file transfer protocol when using HF,VHF
radio link with a digital modem.

I tried the Zmodem with crash recovery in MS Hyper Terminal to transfer
relatively small files but the transmission fails at the first bad
packet

But I should restart the transfer every time

You don't have to restart the whole transfer for a single failed packet.
Make up your own protocol. Divide the file up into packets that aren't too
long. Add a message number and a packet number to the front of the packet and
calculate a checksum for each packet and send that at the end. Wait for the
receiving end to acknowledge each packet. If the packet gets corrupted, then
the receiving end sends a nak or negative acknowledge. If you don't get
anything back or if you get a nak, then you re-send the packet until it gets
through.

Jim

 

[John Smith]

esamsalah@gmail.com wrote:

What is the most suitable file transfer protocol when using HF,VHF
radio link with a digital modem.

I tried the Zmodem with crash recovery in MS Hyper Terminal to transfer
relatively small files but the transmission fails at the first bad
packet

But I should restart the transfer every time

I think that Zmodem is a full duplex protocol and digital radio modems
operates on a half duplex manner

So Zmodem times out waiting ....

Any advice or suggestion is welcomed

Essam Salah

Try Kermit...

http://www.columbia.edu/kermit/

 

[BobG]

Over on avrfreaks, the opinion is that rs232 style NRZ encoding has a
DC bias/average DC level per character that messes up the receiver
threshhold detector. They claim that manchester encoding has a zero dc
level, so long runs of 000 or FFF dont confuse the receiver.

 

[Luhan Monat]

I think that Zmodem is a full duplex protocol and digital radio modems
operates on a half duplex manner

Hi,

Thats the crux of the matter. The best you can do with one-way
communication is to attach checksums to to blocks of data and at least
know when you receive a bad one. Anything more gets real complicated.


--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm

 

[Michael Black]

(esamsalah@gmail.com) writes:

What is the most suitable file transfer protocol when using HF,VHF
radio link with a digital modem.

Track down what they used on AlohaNet in the early seventies in Hawaii.

First packet radio.

A few years later, one of the people connected with it, or maybe it
was just influenced, I forget, had a position with the DOC here in Canada,
and decided packet radio was what amateur radio needed. Hence the
first display of amateur packet radio here in Montreal back in May of 1978.

So look up amateur packet radio. It's been around all these years.

Michael

I tried the Zmodem with crash recovery in MS Hyper Terminal to transfer
relatively small files but the transmission fails at the first bad
packet

But I should restart the transfer every time

I think that Zmodem is a full duplex protocol and digital radio modems
operates on a half duplex manner

So Zmodem times out waiting ....

Any advice or suggestion is welcomed

Essam Salah

 

[BobG]

Why not send every byte 3 times and take the one that gets received 2
or 3 times? Of course, that doesnt give much of a clue of what to do if
you send 3 bytes and get 3 different received bytes.... maybe send 3
bytes with parity? Yeah... that might work.... 200% overhead, but
reliable.....

 

[Guy Macon]

BobG wrote:

Why not send every byte 3 times and take the one that gets received 2
or 3 times? Of course, that doesnt give much of a clue of what to do if
you send 3 bytes and get 3 different received bytes.... maybe send 3
bytes with parity? Yeah... that might work.... 200% overhead, but
reliable.....

Better to send the entire message three times. Radio interference
tends to come in bursts which would wipe out several bytes in a row.

 

[keith]

On Wed, 23 Feb 2005 19:52:11 +0000, Guy Macon wrote:

BobG wrote:

Why not send every byte 3 times and take the one that gets received 2
or 3 times? Of course, that doesnt give much of a clue of what to do if
you send 3 bytes and get 3 different received bytes.... maybe send 3
bytes with parity? Yeah... that might work.... 200% overhead, but
reliable.....

Better to send the entire message three times. Radio interference
tends to come in bursts which would wipe out several bytes in a row.

Or stir the bits before sending. All ECC methods must be tailored for the
expected failure modes.

--
Keith