haas@utah-cs.UUCP (Walt Haas) (04/14/84)
Tymnet does indeed offer an X.25 interface. It is basically not correct to talk about any public data network "being" an X.25 network in any sense except that they do or do not provide an X.25 interface. Telenet is X.75 internally, whereas Tymnet uses a protocol of their own design which repackets data within the network. None of the large public data networks in the US uses X.25 internally, since it is not really well suited to that purpose. X.25 does however work fine as the internal protocol of a relatively small regional network, and indeed ComWest, which is a small public data network serving the State of Utah, is built with Dynapac switches interconnected by the X.25 protocol. The new AT&T offering, ACCUNET* Packet Services, is being planned at present around X.25 as the internal protocol, and it will be real interesting to see how it works out. Currently ACCUNET is not really a network, since they only have two nodes, New York and Chicago, which are not even connected to each other. Of course their reason for existing is to support Net/1000, and they are doing that on a trial basis at present. ACCUNET is supposed to turn into a real network about next January, so by the middle of 1985 we shall see how their idea of using X.25 internally works out in the real world. Regards -- Walt Haas
julian@deepthot.UUCP (Julian Davies) (04/16/84)
"... Telenet is X.75 internally. ..." I don't understand this remark. X.75 is a VC (connection-oriented) protocol for use between two half-gateways; it actually looks very similar to X.25 in the packet formats used, but has some little twists to fit the needs of gateway organization. Is this to say that Telenet treats every node as a separate subnetwork, with 'gateways' between them? Julian Davies
rpw3@fortune.UUCP (04/19/84)
#R:utah-cs:-270400:fortune:3100004:000:1537 fortune!rpw3 Apr 18 20:34:00 1984 +-------------------- | "... Telenet is X.75 internally. ..." | I don't understand this remark. X.75 is a VC (connection-oriented) | protocol for use between two half-gateways; it actually looks very | similar to X.25 in the packet formats used, but has some little | twists to fit the needs of gateway organization. Is this to say that | Telenet treats every node as a separate subnetwork, with 'gateways' | between them? | Julian Davies +-------------------- I don't know about Telenet, but when XTEN (R.I.P. *sigh*) was looking at packet switches a few years ago, we looked at the Siemens EDX-P, and that's EXACTLY what they do. Every node is a separate sub-net, and talks X.75 to it's neighbors (but ONLY X.25 to "subscribers", puh-lease! ;-} ). I was also very curious about that, since there are much more convenient and efficient "internal" protocols for inter-nodal intra-network transport. What I was told is, "Look, outside the U.S, our customers are the various PTTs, and most countries that buy our gear are only big enough for one, maybe two, nodes. They have to talk X.75 across the international borders, so we just made it easy for ourselves and use it everywhere." Now it would seem that Telenet is big enough to employ more efficient ways of internal transport, but maybe they just decided to "make it easy" and not bother, likewise. Rob Warnock UUCP: {ihnp4,ucbvax!amd70,hpda,harpo,sri-unix,allegra}!fortune!rpw3 DDD: (415)595-8444 USPS: Fortune Systems Corp, 101 Twin Dolphin Drive, Redwood City, CA 94065