"hitting" the server should be a matter of sub-1k-byte of transfer.

Of course, none of us have gotten to sniff it yet - but my imagination suggest a request-file-doesn't-exist-ack. That's only a few hundred bytes.


SimpleRequest
Content-Type: plain/text;
GET <file://filename or http://filename> CrLf
HTTP/1.1

Or along those lines... Real bits don't come into play until a file is actually there for download.