Re: File transfer protocol for Radio Links

From: James Meyer (jmeyer_at_nowhere.net)
Date: 02/17/05 

Date: Thu, 17 Feb 2005 12:56:48 GMT

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

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