Re: File transfer protocol for Radio Links

From: Allan Herriman (allan.herriman.hates.spam_at_ctam.com.au.invalid)
Date: 02/17/05 

Date: Fri, 18 Feb 2005 04:48:45 +1100

On Thu, 17 Feb 2005 17:22:10 +0000, Iwo Mergler
<Iwo_dot_Mergler@soton.sc.philips.com> wrote:

>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
>>
>You could try PPP and run any flavour of Internet
>protocol over it. They all do checksums and sequence
>numbers and TCP based ones (FTP,HTTP,etc) handle lost
>packets.
>
>I'm not using MS Windows myself, but I believe somewhere
>among the internet stuff you have everything you need
>to set up a computer-to-computer PPP link. If not, you
>can most definitely download some PPP software for free.

For a (noisy) radio link, it might help to reduce the MTU to perhaps a
few hundred bytes. Normally, this would hurt throughput, as more
packets are needed to send the same information. But when the BER
gets bad (say, 1e-3), the shorter packets will have a much better
chance of getting through than the regular 1500 byte packets.

Regards,
Allan

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