RFC 451 (rfc451) - Page 2 of 3
Tentative proposal for a Unified User Level Protocol
Alternative Format: Original Text Document
RFC 451 Unified User Level Protocol Proposal February 1973 why not simply put hooks in Telnet to indicate that a Network Generic Function is wanted instead of a Host-specific one at a given point in time? Then everybody can come in through Telnet in ways that are already known (and usually debugged and optimized) and fan out to other services through a single mechanism, where that single mechanism can be whatever is most appropriate to a particular Host. This view has the additional virtue of keeping the Host "Answering Service"-equivalent processes out of the act when new protocols come along -- where by Answering Service, I mean that process which manages logins in general for a given Host. This process is, of course, a particularly sensitive one on those systems which worry about accounting and security. That's all probably a bit vague. Perhaps some idea of how I think the UULP would work will cast some light on what I think it is. What's needed is a way of letting the Server know that it's being given a generic command (I decline to call it a Network Virtual command, but I'm afraid that might be what I mean) like "STOR" or "RETR" rather than a local command like "who" or "sys". What could be simpler than defining a Telnet Control Code (TCC) for "Network Generic Function Follows"? So if the Server Telnet receives a command line beginning with the NGF TCC (say, 277 octal), it just feeds the line to the appropriate process or procedure (depending on the structure of its operating system). This approach also offers a handy way of communicating back the fact that a particular protocol or piece thereof isn't available: define a TCC for "Unimplemented Generic Function". This feels a lot cleaner than having a close on socket 3 mean anything from "no FTP Server exists here" to "the FTP Server happens to be busy." Notice that the UULP automatically provides the answer to such objections as the one Braden raises in RFC 430, that "there is no mechanism within the FTP for _changing_ a password. A user shouldn't have to use a different protocol ... to merely change his password". With the UULP, any system which has a password changing ability would have it available for all user level protocols because all of its abilities are made available by the generic login. This seems clearly superior to having to retrofit afterthought after afterthought to the various user level protocols as we come to realize that life is more convenient when we get away from the view that each protocol lives in its own island universe. I understand that one of the main motivations for going the multiple contact socket route was to avoid syntactic (and semantic) conflicts between the protocol and the particular Host's "normal" command processor; however, locking ourselves in to special command processors exclusively is awfully procrustean. So instead of cutting off the limbs to fit the bed, why not use the UULP to expand the bed. Padlipsky
