pag@hao.UUCP (Peter Gross) (12/31/83)
In reading the documentation for Interlan Ethernet gear, I noticed a section giving examples of typical Ethernet configurations. The simple case had just one cable segment with multiple transceivers. A more complex example showed two separate Ethernet coax segments, apparently connected by a repeater. It looked like the repeater was between the two segments, and connected to them by transceiver-like connections. My questions: does anyone know what type of cable is used to connect a section of Ethernet coax to a repeater? Is is transceiver cable? If so, the spec says these can only be 50m long. Or is it Ethernet coax? If so, then the only use of a repeater would be to go beyond the 500m limit of cable sections. Anyone know of who makes repeaters? The way I see using a repeater -- if it uses transceiver cable, not coax -- would be as a cheaper way to connect distant Ethernets within a large building (or perhaps even in separate buildings), saving on cost of coax. Am I barking up the wrong tree? --peter gross hao!pag
mark@umcp-cs.UUCP (01/01/84)
DEC just announced a line of repeaters, optical. I don't know much about
them though.
--
Mark Weiser
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!mark
CSNet: mark@umcp-cs ARPA: mark@marylandrpw3@fortune.UUCP (01/01/84)
#R:hao:-77800:fortune:5900004:000:3679
fortune!rpw3 Dec 31 22:18:00 1983
May I strongly recommend reading the original DEC/Intel/Xerox document,
"The Ethernet: A local Area Network; Data Link Layer and Physical Layer
Specifications", Version 1.0, Sept. 30, 1980. It's easily available
from any of the three companies, for free. It answers all of your
questions, especially in the area of repeater configurations. (Some
small changes are made in the 2.0 spec, to come closer to IEEE-802.)
However, to save some hassle:
My questions: does anyone know what type of cable is used to
connect a section of Ethernet coax to a repeater? Is is
transceiver cable?
Yes, since a repeater is just a "station" with a "controller", like any
other (as far as the transmission rules go). It therefore attaches to each
of its cables with a transceiver. From the spec, Section 7.1.4.1, "Repeaters
are implemented using standard transceivers, plus a simple, non-buffered
finite state machine." Contrast this with address filters or gateways, which
have packet buffers and routers (and therefore CPUs) in them.
If so, the spec says these can only be 50m long.
Yes, 50m on each side, for a total of 100m between the cable segments.
However, see the D/I/X spec, Section 7.1.5 "Channel Configuration
Model", Figures 7-1a, -b, and -c, and 7.6.4 "Repeaters" for a
discussion of point-to-point links which are (logically) within a
"single" repeater.
...then the only use of a repeater would
be to go beyond the 500m limit of cable sections.
The main uses of repeaters are to go beyond the 500m length of one
cable segment and to connect more than 100 stations to a single
network. (The maximum number of stations/cable = 100, limited by the
A.C. and D.C. limits of the transceivers, taps, and cable. The max
number of stations/net = 1024, limited by the collision/backoff
algorithm.)
Another use is "...to provide additional topological flexibility
[7.1.4.1]", for example, to allow ready reconfiguration of the
network(s) to facilitate trouble shooting or load balancing.
(The 48-bit absolute address assures having no addressing hassles if
you do this. Imagine shuffling all the sub-nets around with an 8-bit or
6-bit address per station you have to keep unique and correct!)
Anyone know of who makes repeaters?
I think DEC does, check their mail-order catalog. Also try Intel. Interlan
will sell you one (made by someone else?).
The way I see using a repeater -- if it uses transceiver cable, not
coax -- would be as a cheaper way to connect distant Ethernets within
a large building (or perhaps even in separate buildings), saving on
cost of coax. Am I barking up the wrong tree?
Not at all. This is EXACTLY what the "internal point-to-point link" inside
a repeater is for. That link can be fiber, microwave, coax, etc., as long as
it satisfies the propagation delay requirements of section 7.1.5, Item 5:
"A maximum of 1000 meters of point-to-point link anywhere in the system.
This will typically be used as a way of linking cable segments in different
buildings. Note that a repeater with this internal point-to-point link can
be used to repeat signals between segments many hundreds of meters apart.
The worst-case propagation velocity of the link cable is assumed to be .65c
[ed: c = speed-of light]; the round-trip propagation delay for 1000 meters
is 10.26 us [microseconds]."
Again, the Ethernet spec is especially notable for being implementable.
You can use it directly and be assured that your implementation will be
(at the data-link level) compatible with others.
Rob Warnock
UUCP: {sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3
DDD: (415)595-8444
USPS: Fortune Systems Corp, 101 Twin Dolphins Drive, Redwood City, CA 94065salkind@cmcl2.UUCP (01/02/84)
#R:hao:-77800:cmcl2:400001:000:89 cmcl2!salkind Jan 1 23:39:00 1984 Ungermann-Bass makes a remote repeater that uses a fiber link. The price is around $7K.