Sorry, xmodem is the only one I've got. Coding a transfer protocol is getting right inside the operating system because you have to grab that packet and save it quickly. It is a long story, but suffice to say that it took many people working over several months last year to get it working. Before July last year getting a program onto a N8VEM meant putting it into an eprom. I can't take credit for fixing xmodem for the n8VEM but more recently I have subsequently coded both the Tx and Rx halves of xmodem in vb.net so I have an understanding how it works. It would be one of the simplest protocols around so if it doesn't work then more complex ones probably won't either. It sends a packet then waits for a NAK or ACK byte. If either of those two bytes didn't go through then it would wait 5 secs or so and then resend. So you would see it slowing down. I don't think that is what we are seeing. Rather, I think the 128 byte packet plus the checksum is not going through. I got two errors - one said "short packet" and the other said "checksum error". The short packet one is interesting because it suggests that the first bit of the packet went through, and the last bit with the checksum, but there were not the full number of bytes. So some bytes went missing somewhere in the middle.
Where would they go? Maybe they didn't get all round the world via the internet. But then again, I get the same errors logging in locally. So maybe they are getting lost in Leif's program somewhere. Perhaps the program polls the serial port, and in that brief moment it misses the next byte coming in via winsock.
At least I can replicate this error locally so I can work on it.
Re wireless, I do have xmodem sending files wirelessly between boards at 1200 baud. That works really well all through the house and outside as well. Uses these modules
http://www.yishi.net.cn/index.asp?id=47 (eg the YS-1020U#) Lots of modules have been tried but only these ones in this series can do file transfers because they have a 256 byte buffer. Most modules are 32 or 64 byte, which is too small for xmodem. All the ones on that page are interchangeable - all that is different is the power rating. The 10mW ones are fine round the house. The 500mW ones are overkill and indeed won't work less than 2 metres apart and tend to make CRT displays wobble when they transmit. But they work great outside when you put them up on a high pole. And all the modules in that series have the same plug so you can drop in the right power one for the job. I made a little adaptor board to convert to a D9 RS232 plug. If you are going down that road let me know because I've got 100 of those little boards and I'll never use them all and would be happy to give some away.
I have pondered coding a bittorrent protocol. Ie one that can be terminated in the middle of a file and resume whenever a connection is there, and can handle noisy lines and won't crash on long files on the very last packet. It could be a fun project.