Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!mcsun!ukc!edcastle!spider!raft.spider.co.uk!keith From: keith@spider.co.uk (Keith Mitchell) Newsgroups: comp.protocols.tcp-ip Subject: Re: LAT vs telnet Message-ID: <1991May3.132712.26300@spider.co.uk> Date: 3 May 91 13:27:12 GMT References: <154113@pyramid.pyramid.com>,<1991May2.012159.23962@megadata.mega.oz.au> Sender: news@spider.co.uk (USENET News System) Organization: Spider Systems Limited, Edinburgh, UK. Lines: 92 Nntp-Posting-Host: orbweb.spider.co.uk In <1991May2.012159.23962@megadata.mega.oz.au>, Andrew McRae (andrew@megadata.mega.oz.au) writes: > My real question is: If the concept of LAT is good enough, and the > advantages great enough, why doesn't someone define a protocol that > does the same job, but is part of TCP/IP; in other words a local telnet > protocol. I guess the biggest problem (as with some many other protocols) This has always struck me as a good idea. Some time ago there was dicussion of why rlogin was a "better" protocol than telnet. It turned out that it is no such thing, it is not the telnet *protocol* that was lacking, just most *implementations*. I believe the IETF Telnet WG has addressed most of these issues now, if not all vendors. Unfortunately, for LAT vs, Telnet, it is rather different. There are some fundamental differences in the nature of the protocols that mean LAT functionality cannot just be glued onto Telnet, as implied by lstowell@pyrnova.pyramid.com (Lon Stowell) in <154113@pyramid.pyramid.com>: > How about just adding a block or full screen mode option to > Telnet? tn3270 is somewhat what I mean, but not quite. > > User input would be edited, parsed, etc. at the entry point, > then forwarded into the network only when an Enter key is > pressed...or a Function key. I don't know much about tn3270, but I think I know enough about LAT to say you have missed the point here. It sounds to me that you are proposing something like Telnet Line Mode, i.e. buffer the input from a user up until some trigger character before forwarding it in a packet, instead of forwarding a single-charater per TCP packet. This is not really why LAT is more efficient. What makes LAT more efficient than telnet (over single LANs at least) are: - It multiplexes all the user sessions between one terminal server and host into a single virtual circuit, instead of one circuit per user. This amortises per-packet processing over many users. - There are fixed time-slots for when packets are forwarded from server to host. With Telnet these are generally variable. The other thing about LAT that is nice is the concept of "services" rather than hosts. You can have multiple services per host, or multiple hosts per service. In theory you can do this stuff using TCP/IP, in practice many implementations are not up to. To emulate this properly over TCP/IP, you would probably need to do what LAT does and multicast service advertisements. How many vendors ship IP with Multicast capability ? Other LAT pluses include service access control, and well-defined remote printing. Despite these diffculties, I still think something like this is do-able, and desirable if "we" (the Internet *open* systems people) are to fight back "them" (the properiatary DECNet, Novell, Appletalk *closed* systems people). The most common argument I hear against open systems is - "Yes, but if I buy all my kit from vendor X, it can do feature Y..." These are valid complaints, and we need to look at why our current systems can't do Y. LAT is a major case in point here. Back to : > protocol. I guess the biggest problem (as with some many other protocols) > is that LAT got there first, and no one is going to support any MORE > terminal protocols; but if an RFC was written, and an implementation > done, and the bugs ironed out.... > > Has anyone attempted to define or build a public domain LAT-style > local terminal protocol? If DEC would loosen up on LAT, that would > solve the problem, but is that likely? I would have thought this was something our ISO friends should be looking at. I doubt that DEC are likely to put LAT into the public domain, when there are so many patents etc attached to it. I don't think VTP can do this, and I have not heard of any LAT-like open standard. The only the other procotol I know remotely like LAT is Prime's LTS, which although still proprietary, at least runs over LLC2. Keith Mitchell (postmaster) Spider Systems Ltd. Spider Systems Inc. Stanwell Street 12 New England Executive Park Edinburgh, Scotland Burlington Phone: +44 31-554 9424 MA 01803 Fax: +44 31-554 0649 +1 (617) 270-3510 keith@spider.co.uk keith%spider.co.uk@uunet.uu.net ...!uunet!ukc!spider!keith zspz01%uk.ac.ed.castle@nsfnet-relay.ac.uk