zweig@cs.uiuc.edu (Johnny Zweig) (11/06/90)
I was talking to Van Jacobson last week and he described a service his local telco is going to offer real soon now in which the customer sets up virtual calls using the D-channel and then dumps HDLC frames onto the B-channel and they get routed by the CO switch. Zounds! This sounds really neat -- the functionality of IP coming right out of the funny-looking ISDN jack on the wall. Does anyone know more about this service? I am mostly interested in how reliable the frame delivery would be, whether frames would be delivered in order, whether one could set up calls to the same destination over both B-channels in a PRI (to crank out 128kbps to a single other machine) and that sort of thing. Johnny ISDN
goldstein@delni.enet.dec.com (Fred R. Goldstein) (11/07/90)
In article <14396@accuvax.nwu.edu>, zweig@cs.uiuc.edu (Johnny Zweig) writes... >I was talking to Van Jacobson last week and he described a service his >local telco is going to offer real soon now in which the customer sets >up virtual calls using the D-channel and then dumps HDLC frames onto >the B-channel and they get routed by the CO switch. Zounds! This >sounds really neat -- the functionality of IP coming right out of the >funny-looking ISDN jack on the wall. >Does anyone know more about this service? I am mostly interested in >how reliable the frame delivery would be, whether frames would be >delivered in order, whether one could set up calls to the same >destination over both B-channels in a PRI (to crank out 128kbps to a >single other machine) and that sort of thing. Frame Relay Service is, as you say, based upon using the D channel to set up calls and the B channel (OR the D channel, on a low priority basis) to send the bearer frames. The bearer frame uses the "Core Aspects of LAPD" protocol (ANSI T1.6ca, partially through balloting, and also a subset of CCITT draft Q.922), which has an HDLC flag, CRC, and LAPD address, but NO HDLC control info. (That's payload, in a higher layer.) It does not guarantee frame delivery, but what frames it delivers should be in order (under normal circumstances). Two separate B channels would normally be two separate packet streams, though a 128 kbps access to the packet handler (bit-synchronized) isn't inconceivable for the future. Private FR switches, of course, can have faster accesses; you can also theoretically use ISDN H channels (384 kbps, 1.472 and 1.536 Mbps). We spent _years_ working on this at ANSI T1S1... Fred R. Goldstein Digital Equipment Corp., Littleton MA goldstein@delni.enet.dec.com voice: +1 508 486 7388 Do you think anyone else on the planet would share my opinions, let alone a multi-billion dollar corporation?
fleming@uunet.uu.net (11/08/90)
> Does anyone know more about this service? I am mostly > interested in how reliable the frame delivery would be, > whether frames would be delivered in order, whether one could > set up calls to the same destination over both B-channels in > a PRI (to crank out 128kbps to a single other machine) and > that sort of thing. Frame delivery would be unreliable by design. Error-checking and retransmission becomes the responsibility of the terminal (Application Layer), not the network. This mindset change lets you rip out most of the overhead associated with X.25 and start packetizing at 1.5 Mb/s (today ... faster soon). Frames would maintain sequence since you are setting up virtual circuits (connection-oriented). "Both B channels in a PRI" -- a PRI has 23 B channels. And yes, you can dedicate all 23 of them to a single virtual circuit. I haven't seen frame relay promised yet for BRI (2B+D), but it is certainly feasible. There's a decent non-technical tutorial on frame relay in the October issue of Telecommunications magazine (Disclaimer: I wrote it). Let me know by E-mail if I can help. Stephen Fleming | Internet: fleming@cup.portal.com Director, Technology Mktg. | CI$: 76354,3176 AOL: SFleming Northern Telecom | BIX: srfleming X.500: ??? 7900 Westpark Drive, A220 +---------------------------------- McLean, Virginia 22102 | Opinions expressed do not (703) 847-8186 | represent Northern Telecom.
benyukhi@uunet.uu.net (Ed Benyukhis) (11/09/90)
In article <14396@accuvax.nwu.edu>, zweig@cs.uiuc.edu (Johnny Zweig) writes: > I was talking to Van Jacobson last week and he described a service his > local telco is going to offer real soon now in which the customer sets > up virtual calls using the D-channel and then dumps HDLC frames onto > the B-channel and they get routed by the CO switch. Zounds! This > sounds really neat -- the functionality of IP coming right out of the > funny-looking ISDN jack on the wall. > Does anyone know more about this service? I am mostly interested in > how reliable the frame delivery would be, whether frames would be > delivered in order, whether one could set up calls to the same > destination over both B-channels in a PRI (to crank out 128kbps to a > single other machine) and that sort of thing. The way you describe the connection and looking at the data transfer rate, you are referring to a BRI and not a PRI. The subject, of your post semms to suggest that you want to know more about Broadband ISDN services and recomendation. Frame Relay Service is really an OC-1 CCITT standard that is being implemented with laboratory equipment and in laboratory conditions at this point. If it is a BRI that you want know about, as it is currently implemented on some CO switches, here it is: B-channel connection can be provisioned with either packet or circuit services or both on-demand (ODB). All connections over the B-channel are set-up via D-channel Q.931 control messages. However, in the case of a circuit switched connection, layers 2-7 are not defined nor used. Users can/should provide their own synchronization and error control mechanisms. In the case of the Packet Switching over the B-channel, layer 2 is LAPB and layer 3 is X.25. You get your basic synch, error correction and the flow control with these two layers. Yes, PVC guarantees that frames will be delivered in order, and yes, both B-channesl can be routed to the same destination address. I am not really sure if this is what you are looking for of if it is different ISDN services you are interested in. Drop me a line if you want to find out more about ISDN or BISDN. Regards, Edward Benyukhis, Motorola, CIG (708) 632-4658