Uploading/Downloading stability

[Richard Miller]

My Rev program needs to upload and download a file of roughly 2 MB in 
size 3-8 times every 30 minutes via a wireless connection. This 
wireless connection is through the built-in airport card in an IBook. 
Sometimes this connection is received via a wired DSL or cable modem 
(and wireless router), but sometimes it feeds off a Powerbook connected 
to the net via a Verizon 3G PCMCIA card (using Apple's Internet Sharing 
capabilities).

Using the 3G card is obviously less stable than a direct wired 
connection, especially in more rural areas. Sometimes the Internet 
connection just drops off during the middle of the upload or download. 
I'd like suggestions for the most stable way of transferring these 
files, and secondly, what I can do if the file transfer is interrupted 
part way through.

For example, does it matter if I use:

- get URL
- libURLDownloadToFile
- read from socket
- load

Are any more reliable for dealing with 2 MB files via a slower 
connection or just in general?

Secondly, if a file is partly transferred, is there any way to restart 
the transfer from where it left off?

Thanks.
Richard Miller
Imprinter Technologies