jdreyer@bbnccv.UUCP (Jon Dreyer) (08/27/85)
>>> I have no idea how you are >>> supposed to get through a virtual circuit oriented X.25 bottleneck to >>> send IP packets out over the ARPANET, this must make an interesting story. >> >>We are one of the relative handful of sites running the CSNET IP/X.25 >>interface, so I can describe it and our experiences in some detail. RFC-877 >>specifies a standard for the transmission of IP datagrams over X.25 virtual >>circuits. >That's not what I meant, Phil. You aren't on the ARPANET, you're on CSNET, >which is one of the networks in the ARPA Internet. As you point out, being >on CSNET is not as good as being directly on the ARPANET, because you have >to use X.25 virtual circuits underneath your IP datagrams. Obviously this >is silly, but it does have and clear advantage that it works. > >As I understand the situation, people plugging directly into the REAL LIVE >ARPANET (the one you have to know somebody in the pentagon to get onto) >are now being told that the preferred interface is no longer 1822, it's >X.25. This is what I don't understand. > There are a couple of misunderstandings going on here. I'll try to cloud the situation with some of my own: 1. Arpanet IMPs can be configured to provide X.25 service instead of 1822. At the moment, there is no communication between the X.25 subnet and the 1822 subnet. Vanilla X.25 hosts can be plugged into the X.25 subnet and communicate. I believe this is called "basic" X.25 service. 2. There is something called "interoperability" that is being implemented. With interoperability, IP hosts may communicate with each other even if one is connected to the X.25 subnet and the other to the 1822 subnet. The IP hosts on the X.25 subnet must encapsulate IP datagrams in X.25 complete packet sequences more-or-less according to RFC-877 mentioned above. I believe that this is called X.25 "standard" service. Interoperability may be simply implemented by having an IP gateway between the X.25 and the 1822 subnets, but the IMPs are currently being modified to do this themselves. 3. CSNET really isn't a network at all, but rather an administrative collection of subscribers. They use at least the ARPA Internet (including the Arpanet), Telenet and Bitnet for their communication. CSNET subscribers connected to Telenet must use RFC-877 encapsulation. Disclaimer: While I have been involved with the work that led to RFC-877 and with X.25 interoperable gateways in the course of my work at BBNCC, I am expressing only my own view of the situation and am not an official spokesperson for anyone. Jonathan Dreyer jdreyer@bbnccv.arpa {decvax,ihnp4,ima}!bbncca!jdreyer