MRC@SIMTEL20.ARPA (Mark Crispin) (01/17/86)
I too am interested in this. I have a 2020 with a KMC11/DUP11 (a.k.a. KDP or DN20-BA) low-speed synchronous interface. I think the KMC11 microcode does some DDCMP handling; I don't have sources for it. So I guess the real question is if there is a de facto standard for IP over a KDP that is nominally microcoded for DECnet? Has anybody successfully used TCP/IP over a 1200 baud link? Is it at all effective at such a low speed? I already have TELNET and reliable file transfer and mail connectivity with "Dialnet" and various tools (e.g. Kermit). I'm somewhat worried that TCP/IP at such a slow speed would introduce enough overhead to reduce my connectivity over "Dialnet", in which case I might want to hold off until I get a faster modem. -------
MILLS@USC-ISID.ARPA (01/20/86)
In response to the message sent Fri 17 Jan 86 07:05:22-MST from MRC@SIMTEL20.ARPA Mark, I know of several ad-hoc synchronous gizmos used to pipe IP grams from one host/gateway to another, including one suggested in RFC-892 which has been used for several years around here. However, we have found DDCMP most popular, primarily because DMA hardware is readily available for the PDP11 (DMV11 for the Q bus). The U Michigan folk also have a nifty interface board for the Q bus that runs LAPB. I suspect several other folk have done similar things. TCP/IP is completely reasonable with most (but not all) implementations known to me at 1200 bps. In fact, I have used these protocols over amateur AX.25 packet-radio links at 1200 bps when one packet in four died. However, some famous TCP implementations croak dismally via such paths, especially when the implementor has not read RFC-889. Dave -------