Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!CHEETAH.NYSER.NET!mrose From: mrose@CHEETAH.NYSER.NET (Marshall Rose) Newsgroups: comp.protocols.tcp-ip Subject: Re: X.400 on TCP Message-ID: <3995.622140615@cheetah.nyser.net> Date: 18 Sep 89 16:50:15 GMT References: <890915.163451.+0200.af@sei.ucl.ac.be> Sender: daemon@ucbvax.BERKELEY.EDU Reply-To: TCP-IP Discussion Organization: The Internet Lines: 34 RFC 1006 (ISO Transport Service on top of the TCP) published in May, 1987, describes a technique that can be used to host any OSI which ultimately uses OSI transport on top of TCP/IP-based internets. The advantage of this particular approach is two-fold: first, rfc1006 provides an emulation of the OSI transport service, as such the OSI application is completely unaware that it is running in an TCP/IP-based environment. From the practical perspective, this means no change in your code. Considering that application code is easily two orders of magnitude more complex, harder to debug, etc., than the lower layers, this is a win. Second, because the underlying paradigm is that of the OSI transport service, you can build a "transport service bridge" between networks with different transport services (e.g., TCP/IP, TP0/X.25, and TP4/CLNP). This bridge effectively shuffles packets between the different networks allowing me, e.g., to have my TCP/IP-only host exchange an X.400 message with an X.25-only host, providing that somewhere there is a dual-homed host running both TCP and X.25 that both hosts can reach. Of course such a bridge theoretically introduces some performance and reliability considerations, but in practice, this hasn't been noticable. A couple of implementations of rfc1006 have been running for a few years now. The original one (mine) has been running in the Internet since March of 1987. Right now, there are several sites running FTAM, VT, MHS, and OSI Directory, in the Internet right now. Of these four, the Directory is the most notable (MHS is still in beta and not widely distributed), as NYSERNet has been sponsoring a white pages pilot for the last couple of months which uses OSI Directory on top of TCP/IP. Summary: problem solved. /mtr