Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!husc6!harvard!spdcc!dyer From: dyer@spdcc.COM (Steve Dyer) Newsgroups: comp.unix.wizards Subject: Re: Is anyone using DMR-11's under 4.3 or Ultrix? Message-ID: <204@spdcc.COM> Date: Thu, 23-Jul-87 22:04:59 EDT Article-I.D.: spdcc.204 Posted: Thu Jul 23 22:04:59 1987 Date-Received: Sat, 25-Jul-87 11:01:09 EDT References: <2183@emory.uucp> Reply-To: dyer@spdcc.COM (Steve Dyer) Organization: S.P. Dyer Computer Consulting, Cambridge MA Lines: 30 Summary: maintenance mode... I've installed and used DMR-11s at 1mb speeds (T1 lines to JVNC between Harvard and MIT) and at 9600 baud (leased analog lines between Mass Micro, UMass Amherst and the CSNET CIC.) I've never ever managed to get two DMR-11s running in DDCMP mode talking to each other. Somehow, neither end would sync up, and sooner or later one end or the other's output queue would fill up so that further attempts would give "no buffer space available." I never bothered to chase this further, because the solution is so easy: just select "maintenance mode" in your config file (from memory, I believe it's "flags 1") and relink your kernel. In "maintenance mode", packets are sent without any link-level protocol other than a simple checksum encapsulation (a packet with a bad checksum received is discarded and doesn't generate an input interrupt.) This is arguably what you want anyway for a TCP link, since a reliable link-level protocol makes the point-to-point link appear as if the "network" is suffering from variable delays, rather than feeding back the retransmission info to the TCP which can presumably do something interesting with the information. I might mention that the error rates on T1 lines are incredibly low (at least in my experience) and that relying on maintenance mode has worked successfully in both high- and low-speed environments. In both cases, the usage was primarily TCP-based; I could imagine that you might run into trouble with UDP or IP-based applications without some sort of transport layer. -- Steve Dyer dyer@harvard.harvard.edu dyer@spdcc.COM aka {ihnp4,harvard,linus,ima,bbn,m2c}!spdcc!dyer