mark.umcp-cs@UDel-Relay@sri-unix (09/08/82)
From: Mark Weiser <mark.umcp-cs@UDel-Relay> Date: 4 Sep 82 12:03:29-EDT (Sat) Our 50 kbit line to the Arpanet arrives next month, I thought I was all prepared by obtaining the IP/TCP kernel from BBN (although I haven't looked at installing it yet), but now I hear a rumor... We want to run Very Distant Host protocol directly on our Vax-11/780 running Berkeley 4.1 Unix. Is this possible? Friends at the University of Rochester tell me they have tried and it doesn't work, only local host support is any good. Help! Do I really need a C30?
dpk@BRL@sri-unix (09/10/82)
From: Doug Kingston <dpk@BRL> Date: 8 Sep 82 4:44:12-EDT (Wed) I can't speak to the condition of the VDH (or HDH) code in 4.1, but even if it worked, you would not want to use it, the system load of doing all the VDH (HDH) protocol on top of TCP/IP is prohibitively expensive. A better solution to your problem of being distant from the IMP, is to buy a pair of ECU's (error correction units) which are manufactured by the same people who bring you the LHDH-11 ArpaNet Interface (ACC, Associated Computer Consultants). These wonderful boxes are designed to be placed between the IMP host port and your CPU interface. The ECU at the IMP end looks like a host, and the ECU at the HOST end looks like an IMP. In the you hook up the best phone line you can get (the one you would be running VDH on) and the ECU do the error correction in hardware to provide an error free link from HOST to IMP. The ECU can look like a DISTANT or LOCAL host on either end, and the ECU is good for all the bandwidth you can give it. Its also a lot cheaper than getting another IMP. Don't let VDH get you down, -Doug-
mo@LBL-UNIX@sri-unix (09/10/82)
From: mo at LBL-UNIX (Mike O'Dell [system]) Date: 8 Sep 1982 09:43:47-PDT With all due respect for the people that did the VDH back in the Dark Ages, the VDH is famous for not working very well. They have been the cause of premature retirement for more than one good ARPAnet software support person. There are persistant rumors that Greg Noel down at NOSC may be working on a VDH driver for 4.1a, but if he gives up, noone would blame him. The best thing to do, if your IMP must be remote from you, is to get a pair of ECU-II's from ACC. The Error Control Units connect to modems between the pair, and to the host, it looks like a local IMP interface, and to the IMP, it looks like a local host interface. ECU's are not perfect, and if you have a really rotten phone line between them, you will have grief, but not nearly as much as with a VDH. The other alternative would be to do an HDH driver, which would actually be doing the world a large service. But I am somewhat curious about your comment about "do I really need a C30?" If you don't have one, who does?? I have been assuming from your questions that you will be remote from some other IMP. Somewhere the must be an IMP HOST PORT to which your machine is attached. -Mike
obrien@RAND-UNIX@sri-unix (09/10/82)
Date: Wednesday, 8 Sep 1982 10:29-PDT I have never actually attempted to run VDH, but everyone I've ever talked to has been very negative about the experience. It is apparently extremely difficult to get the software exactly right for checksumming, etc. the packets from the IMP, and the link is very, very slow. If your phone Co. is good you might try running a local host interface using ACC ECU boxes, which shove 1822 over a phone line using SDLC. These let you run a local/distant host interface over miles and miles of phone line, if your IMP actually has room in it for a local/distant interface. Our own experience in this department has not been sterling, because we have General Telephone here. The link to Rand-Relay is an ECU link over a leased line to an IMP four or five miles away. This link worked just fine until the Rixon-Sangamo T209 modem on the other end blew up, and it hasn't been right since. Our new C-30 eliminates our need for this link. It seems to be a little-known fact that on a Honeywell TIP, the TIP hardware takes up so much rack space that the fourth hookup to the IMP MUST be a VDH. On C-30's this restriction has been removed. That was our situation and is the reason we chose to run with ECU's to an IMP miles away, rather than attempting to run VDH for 50 feet. After Gen. Tel. I'm not sure which alternative was worse.
CCVAX.ron@NOSC@sri-unix (09/13/82)
Date: 10 Sep 1982 01:34:37-PDT The "persistent rumors that Greg Noel down at NOSC may be working on a VDH driver for 4.1a" are no longer valid. Greg quit NPRDC a few weeks ago and the VDH project is now dead. The day after he quit his management scrambled for the $$$ to buy an LHDH and a pair of ECUs. --Ron
greg (09/14/82)
I'm sorry to report that I will NOT be doing a VDH driver for 4.1aBSD. The reason is not the technical difficulty, but politics -- the facility where I worked was transfered (over my protests) to the control of technically incompetent people whose ethics I find questionable. I had no choice but to resign my post. I still hope someone will do it, but I'm afraid it will not be me. MO is wrong on one point, though -- we found the VDH very reliable, once the hardware pecularities were understood. Both the C and the E versions are bitches to drive, but we never had hardware problems with the E and only twice with the C (over a period of about eight years). I wish the CPU had been that reliable.....
greg (09/14/82)
(Line noise seems to have caused a ^D; I'll continue.....) The best bet for people who currently have a VDH is to get some of the magic boxes from ACC as indicated by MO and Doug (and others). I'm told that the measured bandwidth is about ten to fifteen percent less than the most recent version of the VDH driver (I've improved it a lot), but, of course, the host overhead is somewhat less. You pays your money and you takes your choice. -- Greg Noel, now working for NCR ...!ucbvax!sdcsvax!greg
DEDWARDS@USC-ISI@sri-unix (09/14/82)
Date: 10 Sep 1982 1207-PDT In response to the message sent 4 Sep 82 12:03:29-EDT (Sat) from mark.umcp-cs@UDel-Relay Don't know about the VDH support, but you do NOT need a c/30. You can use a pair of ECU's to go the long haul and they allow you to look like a local host (ECU's are built by ACC). Howard Weiss -------