| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 71.1 | answered in TWISTED_PAIR 261.1 | CGOS01::DMARLOWE | PDP 11: MOV -(PC),-(PC) | Tue Nov 03 1992 15:50 | 1 |
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| 71.2 | When is a hub a coax segment ? | SAC::LANG_H | Button up your overcoat | Wed Feb 03 1993 13:55 | 43 |
| Hi,
Yes, even after all these notes, I am still a little unsure as to
the 5-4-3 rule (5 segments, 4 repeaters, 3 coax).
Consider the following example...
+-------+ HUB
|9| |9|
|0| |0|---------- Thin wire (coax)
|c| |c|
+-------+
|
| Thin Wire (Coax)
|
|
Is this the maximum configuration that can be obtained with 2
DECrepeater 90Cs, since:
there are 2 thin wire segments leading into the 2 DECrepeater 90s and
also the backplane of the Hub is counted as a segment since we are
coming in on one repeater and leaving on another.
If the 2 segments of thin wire both went into the same DECrepeater 90,
then would I be correct in assuming that would only count as 2 coax
segments ?
I've been trying to figure out when a HUB is classed as a segment, and
from discussions that I've had with a colleague, we believe its when we
have to travel along the bus to get out onto another repeater.
Thanks for any input.
Harvey Lang
TCC/S
UK
|
| 71.3 | Well... | CGOS01::DMARLOWE | dsk dsk dsk (tsk tsk tsk) | Wed Feb 03 1993 17:19 | 31 |
| This is how I have looked at it for some time.
The workgroup backbone is considered a 65M piece of coax which you can
extend out of the hub. It can be extended 125M from the hub or
up to 55M to a second hub. It still lives by the rules of coax.
So if you have 1 90C in the hub, you have 1 repeater attached to
a piece of thinwire backbone. Don't forget though that the repeater
has 6 segments. Like a DEMPR each segment is repeated to each other
segment. Traffic on port 1 also goes out on port 2 (thru 6). This
is 2 pieces of coax. Same for traffic on port 1 to the backplane.
Traffic goes in one port and comes out all other ports. If you put a
second 90C in the hub you have 2 repeaters (3 pieces of coax maximum)
between any 2 nodes.
seg. 1 seg. 2 seg. 3
---------90C---------------------90C--------
hub backbone
If you have not extended the thinwire from the hub one could argue
that it is so short that you could ignore the fact that it is a
piece of coax. At least in terms of timing. And assuming no segments
over 185M you may find that everything works just great. But if
someone adds coax to the hub or extends some of the segments over
185M then the network may quit working very quickly.
Maybe an engineer could answer better in terms of timing whether
to include the hub as a piece of coax or not. Maybe its too convervative
counting it that way but I know I won't get into trouble in the future
if somebody extends things.
dave
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| 71.4 | The Official Word | EMDS::BUZZELL | | Thu Feb 04 1993 10:12 | 69 |
|
DTAC Technical
Application Center
(DTAC)
Date: November 5, 1992
From: Chris Di Minico
Dept: DTAC
Loc: MLO3-3/E67
Ext: 223-0529
Net: KALI::DIMINICO
Subject: DEChub 90 Ethernet Backplane Configuration Rules
---------------------------------------------------------
The DEChub 90 backplane has a number of configuration
rules and guidelines that must be followed.
o The DEChub 90 backplane is the equivalent of 65
meters of ThinWire cable out of the maximum of
185 meters for a ThinWire segment WHEN the
backplane is connected to a ThinWire Ethernet
segment via the backplane BNC connector.
o The DEChub 90 backplane is the equivalent of 15 stations
out of the maximum allowance of 30 stations WHEN the
backplane is connected to a ThinWire Ethernet
segment via the backplane BNC connector.
------------------
| DEChub 90 |
| Backplane = | T-connector
| - 65 meters |=|-----===-------------=| <- 50 ohm terminator
| ThinWire | ^ |
| - 15 Stations | | +-----------------------+
|----------------| | | Up to 15 Stations |
| | 120 meters of ThinWire|
| +-----------------------+
Backplane BNC
The 65 meters and the 15 connector adjustment is required to
compensate for the losses associated with matching
the impedances between the backplane, with or without
modules inserted, and the ThinWire segment connected to
the Backplane BNC.
This loss does NOT represent the losses associated with the
Backplane itself and therefore the 65 meters should NOT be
counted in ThinWire repeater topologies that are NOT connected
via the Backplane BNC.
|
| 71.5 | Confirmation. | CGOS01::DMARLOWE | dsk dsk dsk (tsk tsk tsk) | Thu Feb 04 1993 10:37 | 35 |
| Chris,
Can I restate your last reply and confirm that what you said was
in fact what I heard?
The 65 meters and the 15 connector adjustment is required to
compensate for the losses associated with matching
the impedances between the backplane, with or without
modules inserted, and the ThinWire segment connected to
the Backplane BNC.
> This loss does NOT represent the losses associated with the
> Backplane itself and therefore the 65 meters should NOT be
> counted in ThinWire repeater topologies that are NOT connected
> via the Backplane BNC.
Does this mean that with the backplane terminated it is not counted
as a piece of coax in terms of the repeater rules?
thinwire backplane thinwire
========90C------------------90C===========
slot 1 slot 2
This is 2 repeaters. Is this 2 or 3 coax segments??
thinwire backplane interhub thinwire backplane thinwire
========90C--------------+=================+-------------90C===========
slot 1 slot 9
This is still 2 repeaters. This should be 3 coax segments and this
configuration should not/cannot be connected to a thick/thin wire
backbone without the use of a bridge.
dave
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| 71.6 | Clear as mud now? | CGOS01::DMARLOWE | dsk dsk dsk (tsk tsk tsk) | Tue Feb 16 1993 13:36 | 14 |
| I'll answer my last entry having talked to Ed at Network Symposium
(aka. NET-U).
If the backplane is terminated then the backplane is not counted
as a coax segment, essentially a zero length segment. Going in a 90C
in slot 1 and out a 90C in slot 5 gives you 2 coax segments and 2
repeaters.
However if the hub is not terminated but has a piece of coax connected
to it then the backplane is counted as a piece of coax. Going in
a 90C in slot 1 and out a 90C in slot 5 or out a 90C in the second
hub now gives you 3 coax segments and 2 repeaters.
dave
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| 71.7 | 10BASEFL Config Rules | VAXRIO::CARIJO | Fernando Carijo' - SME, Rio | Thu Mar 04 1993 14:12 | 15 |
| Hello,
I would like to know what are the configuration rules with the new 10BASEF.
That's to say, is the configuration below permitted? It spans more than 2.5 km,
but it doesn't violate the total delay rule, and I would like to use a
configuration like that.
+----------+ +-------+ +-------+
|Bridge 90 +==========+ DEFMR +===========+ Bridge+
+----------+ 1.5km +-------+ 2km +-------+
Delay permitted (aprox) : (5 x 2165) + (4 x 2670) = 21505 ns
Delay in the cfg above : (7 x 2500) + (1 x 2670) = 20170 ns
Carijo'
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