zweig@cs.uiuc.edu (Johnny Zweig) (02/16/91)
I heard awhile back (and posted a question or two) about ISDN Frame Relay service in which I treat my local central office as a packet-switch and dump HDLC frames (recall they have eught-bit addresses in them) onto the B-channel of my ISDN BRI and let the switch figure out how to get them where they need to go. I assume there must be some kind of virtual-circuit negotiation on the D-channel to set up the mapping from 8-bit HDCL frame identifiers to ISDN phone numbers (according to Hardwick's book there are both an 8-bit Terminal Endpoint Identifier (address) and an eight-bit Service Access Point Identifier (kind of like a port/protocol-ID) in each HDLC frame). Anyway, rumor has it (actually it was Van Jacobson who said it so it is something more than a mere rumor) that the tariff for this service in the Bay Area will be a flat monthly rate. I would imagine this is more that they haven't actually passed tariffs for it yet than that they think this is a sensible way to bill for a service likely to get used for things like NFS which would send loads-o-frames. Anyway, I could imagine a charge-structure based on a monthly rate, a per-connection charge, a call-duration charge, a per-frame charge, a per-kilobyte charge, or any combination thereof. I don't know how long HDLC frames can be in any actual systems (there is usually a limit, but Hardwick implies it caries from system to system), but I would assume that there is a big difference in per-packet vs. per-kilobyte charging. I am still a little hazy on which kind of stuff (HDLC frames, circuit switched data, etc.) is travelling on which channels at which times (I imagine that 64-kbps circuit switched vs. frame relay is a call setup option...) but if anyone knows of any proposed or actual schemes for charging ISDN users -- especially for frame-relay, since I imagine that will be a big thing for those of us who envision using ISDN to run workstations at home over -- I would love to hear about them. Johnny ISDN