STEWART_SYS@uta.EDU.UUCP (05/27/87)
We have just installed an ethernet backbone in our area and are in the process of installing a DELUA controller on our VAX 11/780. We've been considering DEC's DECserver 200's, Bridge Communications CS100's or CS200's and Ungermann-Bass' Net/One LAN systems. We will be wanting to have access to the VAX and a Harris HCX-7 (Unix) machine initially with AT&T 3B2's, Sun Workstations and possible a TI Explorer added later. Does anyone have any experience with the Bridge or Ungermann-Bass products? The DECservers require DECnet, which we don't know that we really want at this time. The other vendors can use TCP/IP, which seems favorable with the mix of machines that will be on the LAN. If anyone has any war stories associated with these products, or other 'gotchas' that we should be aware of, any info would be appreciated. Thanks in advance... -Dan Stewart The University of Texas @ Arlington STEWART_SYS@UTA.EDU
JMS%uamis@RVAX.CCIT.ARIZONA.EDU.UUCP (11/11/87)
Larry Herzlich writes about DECservers and LAVc nodes. He also includes a quote from Steve Ward. I believe that both of you are making incorrect assumptions. There is NO reason to "de-rate" a CPU because you're using LAT terminals instead of direct terminals. In fact, if you're comparing LATs to Programmed I/O devices, you may "up-rate" your CPU. If you're comparing LATs to DMA devices, you may consider them one-for-one swaps. There is NOT an additional overhead to dealing with LATs that there isn't in direct devices. If you had a DECserver 500 and ALL of it's ports were connected to a VAX CPU instead of having the same number of serial ports, you would see a great efficiency even above normal DMA devices. For 8-port and 32-port LAT servers, we have found the response to be as good as, if not better than, DMZ-32s, Emulex CS21/CS32 combox, DMF-32s and a LOT better than DZ-11s. Also, your comment about saturating the traffic on the LAN with LAT traffic is way off base. We run ALL terminals in this building on LATs (currently there are about 12 LATs worth of terminals) and see short term peaks of up to 3% of maximum bandwidth, but long term traffic is below the 1% level. Do a little arithmetic -- 40 users, right. Input, most users can do a good average (over short time spans) of as many as 3 characters a second. Let's see, that's 40 * 8 * 3 = 960 bits per second. Assume a 300% overhead for this on LAT terminals, that's about 4000 bits per second, out of a possible 10,000,000. For output, let's assume that your users do lots of types and edits and whatever, and are getting as much as 50 characters per second AVERAGE output. 40 users times 50 times 8 is 16000 bits per second, but the overhead is a lot less; say about an additional 50% to make 24000. Now, let's assume that I'm a full order of magnitude wrong on all my numbers (ie, everyone is ten times as active as I said. I'm not actually wrong, but if it'll make it more believable...). You're still using only 25% of your Ethernet. Those out there who know will point out that the fastest we've ever seen a VAX do terminal input is about 2000 characters a second (about 1.6 MHz, again out of the 10 you get on an Ethernet). Synopsis: Don't worry. Put bridges between buildings. It works great. Digital is NOT going to support direct terminal lines except as a black-sheep product. jms +-------------------------------+ | Joel M Snyder | BITNET: jms@arizmis.BITNET | Univ of Arizona Dep't of MIS | Internet: jms@mrsvax.mis.arizona.edu | Tucson, Arizona 85721 | Pseudo-PhoneNET: (602) 621-2748 +-------------------------------+ ICBM: 32 13 N / 110 58 W (I have gotten into trouble too many times to put any faith in disclaimers) "There's nothing here that an overdose of Seconal won't cure."