roy@phri.UUCP (Roy Smith) (11/20/88)
I've recently been asked to help somebody get hooked up to our
ethernet. This guy is a couple of floors down from our ethernet trunk cable
and wants to put a number of things on the net so just running xciever drops
to each of his machines is no good. Also, as this guy doesn't seem to know
anything about computers, programming, or networks, I'd like to have some
kind of isolation between his gear and mine. I can see him unterminating a
cable and bringing down the whole net without realizing it.
Anyway, he's got a couple of boxes with regular DB-15 sockets (uVAX,
DecServer-200) and a number of PC-type boxes with thin connectors. He's also
got a DESPR and a DESTA. So far, the plan seems to be to run a xceiver drop
from my thick backbone cable to his DESPR and then thin ethernet from there,
with his uVAX and DecServer connected via DESTAs.
The question is, just what *is* a DESPR? The Dec-Direct catalog I
have says little of value about the various widgets they make other than to
say that the DESPR is a repeater. What exactly does that mean? If he shorts
out his thin cable, will that do anything bad to my net? Do I have to count
the effective length of his thin segments and the number of taps he has
against the maximum limits of my cable? What about the rule that says you
can't have more than two repeaters between any pair of taps on the network?
Does his DESPR count as a repeater in this sense? What about my DELNI and
TCL multiport xceiver boxes, do they count as repeaters?
--
Roy Smith, System Administrator
Public Health Research Institute
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net
"The connector is the network"vixie@decwrl.dec.com (Paul Vixie) (11/20/88)
Since I'm now surrounded by DEC Ethernet widgetry, I can answer most of this. # The question is, just what *is* a DESPR? The Dec-Direct catalog I # have says little of value about the various widgets they make other than to # say that the DESPR is a repeater. It is. Just look at how big it is compared to a DESTA and you can tell that something serious is going on in there. It's not a bridge, though -- it doesn't filter packets, it just sends them along. # If he shorts out his thin cable, will that do anything bad to my net? Nope. And you don't need to worry about him terminating his thin segment, either. Everyone else on that thin segment should worry -- I suggest you use DEMPRs if they will fit into the logic; DESPR's are useful only inside a single office where there are fewer people to yell at you when you screw something up. # Do I have to count the effective length of his thin segments and the number # of taps he has against the maximum limits of my cable? Sortof. It doesn't affect the number of taps but it does the number of stations. That is, a tap with nobody on it doesn't count (here, anyway). As for length, yes, you need to keep it in mind since the propagation delay from furthest station to furthest station is going up. I'm not sure if the DESPR does CS/MA, if that's what you're asking. It seems like it would have to, and if it does, one of the reasons for keeping the cable short goes away: collision detection domains won't extend past the DESPR. You still have to worry about propagation delay if your protocol cares. (IP/TCP doesn't care, but parts of DECNET do.) # What about the rule that says you can't have more than two repeaters # between any pair of taps on the network? # Does his DESPR count as a repeater in this sense? # What about DELNI and TCL multiport xceiver boxes, do they count as repeaters? Good questions, but you've exhausted my knowledge. Anybody else know? -- Paul Vixie Work: vixie@decwrl.dec.com decwrl!vixie +1 415 853 6600 Play: paul@vixie.sf.ca.us vixie!paul +1 415 864 7013
roy@phri.UUCP (Roy Smith) (11/21/88)
Now that Paul Vixie answered most of my questions about DEC
ethernet widgets, let me add one more that I forgot the first time around.
What's the difference bettween a DESPR and a local DEREP other than the
detail that one has 1-thick/1-thin and the other had 2-thick?
And, if you can stand one more question, who named all the friggin'
boxes? I mean, DE followed by 3 random letters? Can't get much more
confusing than that, especially why you are trying to ask questions over
the phone: "I'm sorry, did you say DEmumble or DEmumble?"
--
Roy Smith, System Administrator
Public Health Research Institute
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net
"The connector is the network"vixie@decwrl.dec.com (Paul Vixie) (11/21/88)
# What's the difference bettween a DESPR and a local DEREP other than the # detail that one has 1-thick/1-thin and the other had 2-thick? I hope someone who knows for sure will answer; I personally think of them as the same thing with different kinds of connectors on each. # And, if you can stand one more question, who named all the friggin' # boxes? I mean, DE followed by 3 random letters? Can't get much more # confusing than that, especially why you are trying to ask questions over # the phone: "I'm sorry, did you say DEmumble or DEmumble?" It's interesting that DELNI has become a generic term. I've heard people trying to order multiport tranceivers end up after giving a long description, just say: "you know, like a DELNI". It's interesting only because I'm not sure if DEC was the first company to make these things... The names all stand for something. Most DEC part names do, believeitornot. DELNI = Digital(?) Ethernet(?) Local Network Interconnect DESPR = Single Port Repeater DEMPR = Multi DEUNA = Unibus Network Adaptor DEQNA = Q-bus DELUA = Lowpower Unibus networkAdaptor (okay, it's poor) DELQA = Q-bus DESTA = (beats me) -- Paul Vixie Work: vixie@decwrl.dec.com decwrl!vixie +1 415 853 6600 Play: paul@vixie.sf.ca.us vixie!paul +1 415 864 7013
pavlov@hscfvax.harvard.edu (G.Pavlov) (11/21/88)
In article <3609@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes: > > What's the difference bettween a DESPR and a local DEREP other than the > detail that one has 1-thick/1-thin and the other had 2-thick? > > And, if you can stand one more question, who named all the friggin' > boxes? I mean, DE followed by 3 random letters? > DESPR = Digital Ethernet Single-Port Repeater DEREP = Digital Ethernet REPeater and then there is the DESTA - Digital (thin-wire) Ethernet Station Adapter. .... etc gets a bit stretched at times, eh ? greg pavlov, fstrf, amherst, ny
smb@ulysses.homer.nj.att.com (Steven M. Bellovin) (11/22/88)
In article <3607@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes: ..... > The question is, just what *is* a DESPR? The Dec-Direct catalog I > have says little of value about the various widgets they make other than to > say that the DESPR is a repeater. Yup, the DESPR is indeed a repeater, with all the benefits and drawbacks appertaining thereto. > What exactly does that mean? If he shorts > out his thin cable, will that do anything bad to my net? Most modern repeaters implement ``auto-segmenting''. That is, if they detect a fault on one segment they effectively disconnect it from the other half, thereby isolating the fault. > Do I have to count > the effective length of his thin segments and the number of taps he has > against the maximum limits of my cable? No, because each segment is separate. On the thickwire end, you're entitled to 500 meters of cable and 100 taps; on the thinwire end, you get 185 m. and 30 taps. More precisely, you're entitled to 60 discontinuities, where a T-connector counts as 2, and a barrel connector counts as 1, on a thinwire segment. Incidentally, when you connect the DESPR to your coax be sure you use a transceiver with *heartbeat disabled*. If you order DEC gear, you need to get the H-4000-BA instead of the H-4000; with other vendors' gear, such as Cabletron, you can field-configure the transciever with or without heartbeat. (DESTAs are also field-configurable, but that's only the thinwire end.) > What about the rule that says you > can't have more than two repeaters between any pair of taps on the network? > Does his DESPR count as a repeater in this sense? Yes, the DESPR is a repeater. > What about my DELNI and > TCL multiport xceiver boxes, do they count as repeaters? No, they're transceivers, and they count as part of the 50 meters of drop cable allowed. The DELNI has a propagation delay equivalent to 5 meters of drop cable; the TCL box is probably in the same ballpark. The best source I know for the configuration rules is a book published by DEC called the ``Network Buyer's Information Guide'', or some such thing; it's reissued a few times a year, and is obtainable from your local DEC salescritter. It goes into great detail about legal configurations, though on occasion it describes a DEC restriction as if it were a generic one. (For example, it says that repeaters -- DEMPRS, DEREPs, DESPRs, or other brands of repeater -- may not be hooked to a DELNI. This isn't even strictly true for a DELNI (as some of the sample configurations show), but it's even less true for some other brands of multi-port transceivers -- but you're not told that....) --Steve Bellovin
ron@ron.rutgers.edu (Ron Natalie) (11/23/88)
DESTA is a thinwire transceiver. I've never figured out why it's called a DESTA if it has a BNC jack and an H4000 if it has an AMP tap. -Ron
tp@granite.dec.com (t patterson) (11/24/88)
In article <922@bacchus.dec.com> vixie@decwrl.dec.com (Paul Vixie) writes: ... ># And, if you can stand one more question, who named all the friggin' ># boxes? I mean, DE followed by 3 random letters? Can't get much more ># confusing than that, especially why you are trying to ask questions over ># the phone: "I'm sorry, did you say DEmumble or DEmumble?" they're fairly pronounceable. most people seem to say the words rather than rattling off the letters one by one. ... >The names all stand for something. Most DEC part names do, believeitornot. > >DELNI = Digital(?) Ethernet(?) Local Network Interconnect >DESPR = Single Port Repeater >DEMPR = Multi >DEUNA = Unibus Network Adaptor >DEQNA = Q-bus >DELUA = Lowpower Unibus networkAdaptor (okay, it's poor) >DELQA = Q-bus >DESTA = (beats me) DESTA = " " Station ThinWire Adaptor (i think) DELUA = " " LAN Unibus Adaptor another popular one is DEREP " " REPeater I cheated -- I looked in the "DEC Direct" catalog -- it doesn't come right out and say what the acronyms stands for, but it hints at them. (The "Digital Dictionary" does tell you, but the 2nd edition I've got here only covers the old stuff like DEUNA.) DEC "Network and Communications Buyer's Guide" -- a great read for a frosty winter night -- no :-) -- goes into further depth so you can get into DECOM, DEFTR, DEPCA, DESVA and DEBET. Oh, yeah, and NIA20. then there's one you won't find in the catalog: DEBAUCH your friendly neighborhood DEC sales rep can either help you find some of this literature or stare blankly and say, "Duh, I dunno. Wanna buy a VAX?" -- t. patterson domain: tp@decwrl.dec.com path: decwrl!tp icbm: 122 9 41 W / 37 26 35 N % opinions herein are mine alone and certainly not those of DEC
ANKGC@CUNYVM.CUNY.EDU (Anil Khullar) (11/29/88)
In article <3609@phri.UUCP>, roy@phri.UUCP (Roy Smith) says: > And, if you can stand one more question, who named all the friggin' >boxes? I mean, DE followed by 3 random letters? Can't get much more >confusing than that, especially why you are trying to ask questions over >the phone: "I'm sorry, did you say DEmumble or DEmumble?" >-- My experience frm DELNIand DEMPR has been horrible: I have had the the unfortunate experience to hook a Symbolics machine to a DECNET via DELNI. I wanted some info on increasing the TMO's and increase the packets to the level that a CHAOSnet (neti:***) function count could handle some open files on the VAX. All I got from a standard colorado hotline was *gee* I do not know what the other (symblics) machine handles. look at NCP > SHOW NODE EXECUTOR Frankly, I think the support *su**s. Not being a hardware oriented guy I'd say that it is easier to run TCP/IP on top of DECNET and hook nonVMS amchines on the same net. (BTW TCP/IP from CMU-TEK is a cheap solution and reasonably worthwile looking into...) >Roy Smith, System Administrator >Public Health Research Institute >{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net >"The connector is the network"
abstine@sun.soe.clarkson.edu (Arthur Stine) (11/29/88)
From article <1749ANKGC@CUNYVM>, by ANKGC@CUNYVM.CUNY.EDU (Anil Khullar): > My experience frm DELNIand DEMPR has been horrible: I have had the > the unfortunate experience to hook a Symbolics machine to a DECNET via > DELNI. I wanted some info on increasing the TMO's and increase the packets > to the level that a CHAOSnet (neti:***) function count could handle > some open files on the VAX. All I got from a standard colorado hotline > was *gee* I do not know what the other (symblics) machine handles. > look at NCP > SHOW NODE EXECUTOR > > Frankly, I think the support *su**s. Not being a hardware oriented guy > I'd say that it is easier to run TCP/IP on top of DECNET and hook nonVMS > amchines on the same net. (BTW TCP/IP from CMU-TEK is a cheap solution > and reasonably worthwile looking into...) > The DELNI and DEMPR have nothing (read: nothing) to do specifically with DECnet or any other protocol for that matter. You could connect the machine via TCP/IP protocols and the hardware is the same. The DELNI is basically 8 transceivers in a box and the DEMPR is a thinwire multiport repeater. Period. They do NOTHING but pass bits... just because they're made by DEC doesn't mean they have ANY relation with DECnet. As far as support, how could DEC possibly know what the DECnet implementation on the Symbolics supports... they didn't do the port!!! Its DECnet, sure, but they didn't write it for the Symbolics... Try going back to Symbolics. They probably won't know anything about it... their DECnet was most likely obtained from Community... Jeez, I hate when people who don't know what they are talking about flame someone or something just because they don't understand how something works. Its people like you who give people the wrong impression of how things really are. Check your facts before you flame... art stine sr network engineer clarkson u