ggm@brolga.cc.uq.oz (George Michaelson) (12/18/89)
ftp doesn't seem to have any concept of unreliable underlying transport or link. I would dearly love to see something like UK-NIFTP's partial file transfer recovery in ftp. (in fact, I believe most uk-niftp don't implement file xfer recovery and rewind the retransmission back to the front) Once you start looking at that sort of functionality, you might wind up agreeing with the OSI reference model which (i think) puts it in session level but given a null session layer you dont have that choice. I guess I'd rather see suitable code in an underlying layer, so that the same functionality was available to ALL TCP-based services, nntp-over-slow-lines and other bulk transfer being obvious candidates. I'm not (quite) silly enough to see everyone hacking their kernel, and nobody is offering invisble glue between TCP and the services, so I guess its a per-service addition or nothing. Why bother? (1) bandwidth is scarce in several crucial places cross-channel links atlantic links pacific links. (2) Point-to-point links are NOT decreasing, SLIP to small boxes and dial-in IP are increasing and thus "noisy" links are just as common dispite backbone upgrades and other net-level advances. (3) IP based services aren't going away for years to come. (4) OSI services can provide this functionality and it might be nice to be able to bridge into Internet services and get the same thing. [err.. can they? I *think* they can...] ACSnet has partial transfer recovery built into the transport(ish) level as well as a multiplexed link level. This is *extremely* useful and far outweighs in my opinion the other (mis?)features of this package/protocol. With its probable demise as the "backbone" protocol across Australia I suspect we are going to see much WORSE service until people learn how to use the IP based services "properly", ("manual" CSMA-CD when slow IP detected a.k.a try again at 3am) Question(s): [history] Was partial transfer recovery considered? If so, why was it rejected? I heard arguments against its implementation on JANET such as "too hard" and "doesn't make sense between divergent h/w or opsys" neither of which I think make sense, especially given machine-independant upper-level encodings like compressed-batch/lempel-ziv/NNTP and hop-based services where you are placed in the role of an intermediate carrier. [whinge] Is it sensible/possible to extend existing product(s) to provide this function? We see Telnet and other extensions, PEP is out, clearly The RFCs aren't rolling over and dying yet. Too late to add into ftp? can it make 4.5bsd? [cringe] Will people be using this feature in OSI applications? does it get turned on automatically or is it missing from most existing setups and thus impossible to use in MHS/FTAM over slow/noisy lines? Enquiring mind wants to know! -George Internet: G.Michaelson@cc.uq.oz.au Phone: +61 7 377 4079 Postal: George Michaelson, Prentice Computer Centre Queensland University, St Lucia, QLD Australia 4067.