Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!bu.edu!xylogics!loverso.leom.ma.us!john From: john@loverso.leom.ma.us (John Robert LoVerso) Newsgroups: comp.protocols.tcp-ip Subject: Re: LAT vs telnet Message-ID: <02May91.231623@loverso.leom.ma.us> Date: 3 May 91 03:51:28 GMT References: <1991May2.012159.23962@megadata.mega.oz.au> Sender: loverso@Xylogics.COM Reply-To: John Robert LoVerso Organization: John & Sue's House, Leominster MA Lines: 34 Return-Path: John Robert LoVerso Don't be give in so easily to those harping LAT as the savior for terminal connectivity. The "expensive" TCP and TELNET protocols only exist in old or poor implementations. In particular, the usually sited "excessive overhead" of TELNET is nothing more than the result of user-level character swtiching in the 4BSD UNIX implemention of telnetd. Changing this design flaw drops almost all the overhead of a TELNET connection such that a typical UNIX host could have 3-4 times as many incoming TELNET connections and still end up with additional free CPU cycles. How do I know? I've tested it!!! (see below) A kludge to the telnetd socket/pty character switching problem was put together back in 1985 or so. The context diffs (from 4.2BSD) are readily available and apply to almost any 4BSD-based OS. Several UNIX vendors actually use the scheme in their product. The correct way to solve the telnetd problem is to re-architecture the means in which ptys and network connections mesh to avoid having a user-space character switch. One such approach involves having both STREAMS-based tty and network code. In this case, a psuedo-terminal STREAMS module just gets pushed on top of the STREAMS stack of the network connection. I know of at least one UNIX vendor doing so already. Mike Karels has said that such a scheme (using bstreams) is in the future for 4BSD. To see the test results yourself, ftp to xylogics.com and grab the files "news.article" and "results.ps.Z" from the directory "annex/unsupported/in-kernel". John -- John Robert LoVerso John & Sue's House, Leominster MA [to reach the corporate puppet: loverso@syn.westford.ccur.com]