At 10:14 AM 4/10/96 -0400, you wrote:

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Various correspondents have pointed out that X.25 is an "open system" in that it is not proprietary. I knew that. I was thinking more of hierarchical vs peer-to-peer. I have been under the impression that TCP/IP connections are more peer-to-peer between different sorts of networks (or nodes) than X.25. Isn't X.25 more of a standard for a single network? Don't X.25 networks need someone more "in charge" than TCP/IP networks, or am I mixing up different layers on the OSI reference model?

X.25 is an interface between a Data Terminal Equipment and a Data Communications Equipment, rather than a whole-network format like IP and TCP. X.25 networks often have random proprietary internals, and they're designed for a world where there IS only one network, because after all, there's only one Phone Company; the X.75 protocol lets X.25 networks talk to each other. But if you look at the higher levels of the protocols, they're not really that different than TCP applications - you've typically got a listener application waiting around for connections from client programs. It feels a bit less peer-to-peer because usually the service you want is the X.3/X.28/X.29 stuff that's X.25's equivalent to telnet, so the server end is a MainFrame, and the client end is a terminal pad that you've connected your 3270 or dumb terminal to. But you can do other things as well, if your computer environment will support it. Simon Spero wrote: } you can call X.25 a lot of things, but proprietary is not one of them. } X.25 did not fail because it wasn't open; X.25 failed because it was crap It's not dead yet, and you can't even say it's failed, given that it's still in wide use in much of the world. X.25 was design to work on networks with really bad bit loss - we're talking modems on barbed wire here, or whatever the French use instead of barbed wire, and in days when computers were _slow_. Yes, it's bureaucratically designed, and parts of it genuinely are ugly, and it does lots of work at Layer 2 that these days you'd do at a higher layer. And, yes, it's a lousy environment to do full-duplex character echo over. But it works ok for a large fraction of the world's data communications, which are designed for less interactive environments. It's fine for email. It's fine for 3270 fill-in-the-blanks applications. It's fine for pre-Web online service applications like CompuServe. It reeks badly for client-server applications which do a dozen little handshakes per transaction, which are designed assuming they're on a LAN and fail badly when stretched across an ocean, but you'll find they often do badly on frame relay as well. Are the Internet and Frame Relay both better ways to do anything than X.25? Yeah. Would I want to do interactive work on it? Of course not. Would I like to do another project getting vendors to modify their X.25 and CLNP to support a set of seldom-used options that some security consultant once convinced one of my customers they needed? No way. Was I susprised that not only does AT&T still use X.25 in some of its older dialup networks, but that it's still very big overseas? Well, yeah :-) # Thanks; Bill # Bill Stewart, stewarts@ix.netcom.com, +1-415-442-2215