kwe@bu-it.bu.edu (Kent England) (01/09/91)
(Please note that this enquiry is posted to three largish groups. I suggest we follow-up on only one group, comp.dcom.lans, and I apologize if you think my posting is too broad.) -------------------------------------------------------------------- I understand a couple of major multiprotocol router vendors will be announcing an ability to operate SNA networks on connectionless internets in the near future. I have a morbid curiousity about how something like this would work, but I understand little regarding SNA networks. I understand that it should be straightforward, after installing a standard sync line in a multiprotocol router, to create a tunnel using your favorite internet protocol, and overlay an SNA or other synchronous network on top of your multiprotocol network. Lots of economies of scale there to make router vendors' accountants and stock analysts everywhere engage in instant Pavlovian responses. However, many moons ago I had a distasteful brush with BSC when I tried out a similar product from a then major (and then independent) vendor of LAN systems that was supposed to run BSC over a broadband datagram network. The product was a spectacular failure, because they did not spoof enough of the BSC protocol features to allow BSC to work reliably over an unreliable network. It seems to me that it could be quite difficult in practice to sufficiently spoof, for the purposes of an unreliable datagram net, BSC or SNA or any other point-to-point protocol that assumes nothing more than a live wire underneath. Does anyone know enough about SNA to know what the pitfalls would be in making it run over a virtual circuit on a connectionless network? [One could imagine all kinds of strange and wonderful things a protocol designer could do if (s)he could safely assume nothing but a wire to run it on. Since we are talking about putting such protocols on top of *virtual* circuits, my questions revolve around what has been done in SNA of this nature that would not work well on a datagram net, and what could an implementor do to satisfy (spoof) SNA requirements for operating acceptably under these conditions.] For example, do SNA lines engage in incessant ENQ/ACK behaviour? Is that easy to spoof? Does SNA assume very tight response time when it sends data? Is that easy to spoof? Are SNA networks designed and tuned so variously that one cannot assume much about what one may successfully spoof? I would appreciate it if all the inevitable harumphing about how awful SNA is could be saved for another day. Thanks. --Kent
PMW1@psuvm.psu.edu (Peter M. Weiss) (01/10/91)
In article <71876@bu.edu.bu.edu>, kwe@bu-it.bu.edu (Kent England) says: > For example, do SNA lines engage in incessant ENQ/ACK >behaviour? Is that easy to spoof? Does SNA assume very tight >response time when it sends data? Is that easy to spoof? Are SNA >networks designed and tuned so variously that one cannot assume much >about what one may successfully spoof? ACF/NCP SDLC circuits contain a multitude (that's being kind) of timing parameters, from how often it (the FEP) polls the slave control unit, to how long it will wait for the poll to be answered. But why bother: how about a channel-attached SNA control unit-to- TCP/IP protocol converter? i.e., I don't believe ACF/VTAM polls local SNA CUs. /Pete -- Peter M. Weiss | pmw1 @ PSUADMIN | vm.psu.edu | psuvm 31 Shields Bldg - PennState Univ.| not affiliated with VM.PSU.EDU | PSUVM University Park, PA USA 16802 | Secrecy is the guardian of bureaucracy