aaron@zippy.telcom.arizona.edu (Aaron Leonard) (01/23/91)
According to my trusty DEC _Telecommunications and Networks Buyer's Guide_ (Jul 90, p. A-14): * A repeater cannot be connected to a DELNI. No explanation, no details. (I recently attended a DEC seminar on Ethernet configurations & asked the instructor for details on this restriction, but only offered a little mumblage.) Is there any inherent limitation in a multiport transceiver that prevents repeaters from being plugged into them? Or is this just some bogosity in the DELNI as built by DEC? Can 3rd party repeaters be plugged into DELNIs? Can DEC DEREPs be plugged into 3rd party multiport transceivers? Can 3rd party repeaters plug into third party multiports? Aaron Aaron Leonard (AL104), <Leonard@Arizona.EDU> University of Arizona Telecommunications, Tucson AZ 85721
nraoaoc@nmt.edu (NRAO Array Operations Center) (01/23/91)
In article <1991Jan22.123047.397@arizona.edu> Leonard@Arizona.EDU writes: >According to my trusty DEC _Telecommunications and Networks >Buyer's Guide_ (Jul 90, p. A-14): > > * A repeater cannot be connected to a DELNI. > >Is there any inherent limitation in a multiport transceiver >that prevents repeaters from being plugged into them? Or is >this just some bogosity in the DELNI as built by DEC? > >Can 3rd party repeaters be plugged into DELNIs? Can DEC >DEREPs be plugged into 3rd party multiport transceivers? >Can 3rd party repeaters plug into third party multiports? A repeater cannot be plugged into a DELNI unless the DELNI is set up so that it does not transmit heartbeat. The repeater, even DEC's own, will interpret heartbeat as a collision. If your DELNI is connected to an external Ethernet (the 9th connector), it should not be transmitting heartbeat. If it is standalone, you will have to get a loopback connector, and flip the little switch to external mode, to prevent this. This is what I was told by a DEC engineer at an "Advanced Ethernet Concepts" tutorial. Since I have never tried it myself (in the one case where I actually had a DEMPR and a DELNI beside each other, I didn't want the DEMPR connected to the external network), I can only assume he knew what he was talking about :-). I know little about the DEREP, so I can't say for sure that it behaves like the DEMPR, but it ought to. The only differences should be the media and the number of connections. The "Buyer's Guide" is set up so that when anyone who reads it follows all the rules, their network is guaranteed to work. A lot of the "don't" rules actually only cover some situations; in other situations, the thing you are told not to do will work, but you have to know what you are doing, and you have to be prepared for it to not quite work right if you screw up :-) . -- Ruth Milner Systems Manager NRAO/VLA Socorro NM rmilner@zia.aoc.nrao.edu
leonard@arizona.edu (Aaron Leonard) (01/24/91)
A consensus has emerged on why you can't plug a repeater into a DELNI.
The story goes something like this (thanks to Kevin Oberman, Cliff
Frost, Steven Lendt, Wayne Sung, Chuck Kollars and Ruth Milner):
1. A repeater must not be connected to a transceiver that
generates SQE.
2. A DELNI will issue SQE on all of its transceiver ports if it
is in LOCAL mode, or if its AUI port is attached to a transceiver
with SQE enabled. (However, if the DELNI's AUI is attached to a
non-SQE transceiver, or if the DELNI is in GLOBAL mode and has a
loopback plug on the AUI, then it will not issue SQE.)
3. DEC tells its customers that you shouldn't plug repeaters into
DELNIs to avoid boggling their little minds (and their field
servants' little etc.)
I do not believe this story for the following reasons:
1. DEC insists that the DEREP *must* be connected to an H4000-A
(heartbeating) transceiver, and *cannot* be connected to an H4005
(non-SQE) transceiver.
2. DEC says that the DEREN (its new repeater) can sense whether it
is attached to a heartbeating transceiver or not, and configure
itself accordingly.
3. DEC has proven itself to be unafraid to publish baroque DELNI
configuration guidelines, in its rules for hooking up DEMPRs
to DELNIs (see _Telecom & Nets Buyer's Guide_ Jul 90 p. A-19.)
The published rules for DEMPRs in fact jibe with the description
above of how to get a DELNI not to issue heartbeat.
A more plausible hint (from Cliff Frost) is that DELNIs "strip
preamble". The mechanics of precisely how this might impact
repeaters is unclear and no doubt over my head.
Let me, then, propose some rules for hooking up repeaters to
multiport transceivers, so that the more knowledgeable among you
might shoot them down:
1. A DEREP can be plugged only into an H4000-A (or any other
transceiver that offers heartbeat), but not into a non-SQE
transceiver, or a DELNI, 'cause DEREPs are old and weird.
2. A DEREN can be plugged into any available transceiver but not
into DELNIs 'cause DELNIs are old and weird.
3. No third-party repeater can be plugged into a DELNI 'cause
DELNIs are etc.
4. Any third-party repeater can be plugged into any non-SQE (802.3)
transceiver or into any third-party multiport transceiver, as long
as the multiport transceiver does not transmit SQE.
[This rule in particular I offer in order to draw flames.]
- Aaronoberman@rogue.llnl.gov (01/25/91)
In article <1991Jan23.143949.400@arizona.edu>, leonard@arizona.edu (Aaron Leonard) writes: > Let me, then, propose some rules for hooking up repeaters to > multiport transceivers, so that the more knowledgeable among you > might shoot them down: > > 1. A DEREP can be plugged only into an H4000-A (or any other > transceiver that offers heartbeat), but not into a non-SQE > transceiver, or a DELNI, 'cause DEREPs are old and weird. N.B. While this is true, please be careful! The DEREP is an Ethernet V2 device, not 802.3 complient. It must be hooked to an Ethernet V2 transceiver. N0 802.3 transceiver (Regardless of SQE) will work properly. Many folks confuse heartbeat and SQE. They are similar but not quite the same. Heartbeat is present on all Ethernet V2 transceivers. SQE is selectable on 802.3 transceivers. Since the H4000-A is about the only Ethernet V2 transceiver available, the DEREP pretty much requires this device for it's connection. > > 2. A DEREN can be plugged into any available transceiver but not > into DELNIs 'cause DELNIs are old and weird. Well, at least weird. But not really old. I just bought one. > 3. No third-party repeater can be plugged into a DELNI 'cause > DELNIs are etc. Actually, you can if you adhere to heartbeat rules. I have done so with no problem. Check the DEMPR manual and you will find that even DEC supports this. > 4. Any third-party repeater can be plugged into any non-SQE (802.3) > transceiver or into any third-party multiport transceiver, as long > as the multiport transceiver does not transmit SQE. > [This rule in particular I offer in order to draw flames.] Hey, this is the only one I can't comment on. (Just because I don't know about very many third party products.) R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything.
phil@brahms.amd.com (Phil Ngai) (01/25/91)
In article <1991Jan23.143949.400@arizona.edu> leonard@arizona.edu (Aaron Leonard) writes: | 3. DEC has proven itself to be unafraid to publish baroque DELNI | configuration guidelines, in its rules for hooking up DEMPRs | to DELNIs (see _Telecom & Nets Buyer's Guide_ Jul 90 p. A-19.) However, the DEMPR came after the DEREP. DEC may have gotten more experience and/or more confidence and/or more dedicated writers. -- When someone drinks and drives and hurts someone, the abuser is blamed. When someone drinks and handles a gun and hurts someone, the media calls for a gun ban.