scj@pandora.bellcore.com (Steve Johnson) (05/04/90)
In article <29556@cup.portal.com> thad@cup.portal.com (Thad P Floryan) writes: ... (much reasonable information deleted) > >Transceivers for "standard" Ethernet (the thick cable) cost either the same >or slightly more than the ones for ThinNet; the standard Ethernet transceivers >have the "vampire" tap that pierces the cable down to the center conductor >(and note you'll probably need a braid pick to poke around the cable). > A quick caution about mechanical vampire taps---the most common. These are the rough equvalents to "snap on" power taps often sold to wire trailer lights to your car's electrical system. And just as prone to failure due to misalignment, corrosion, etc. Beg, borrow or steal coax strip and crimp tools if you must, but avoid mechanical vampire taps unless you like network trouble (think about it---You're going to pass a theoretical 10 mega-bits *per second* thru a *pin* that pierces the coax outer cover, the outer braid, possibly an intermediate cover and braid, and the inner sheath and then "gouging" a mechanical connection onto the approximately 18 guage carrier wire). The cable you're piercing is the backbone, which in commercial environments is often the most expensive part of the LAN. Thick ethernet cable is *tough* stuff. I've seen a vampire tap wrongly installed (by a non-trained individual) literally cut the backbone in two. (brings the LAN down RIGHT NOW).
thad@cup.portal.com (Thad P Floryan) (06/05/90)
Re: Bob Slaski's posting about 3B1 Ethernet equipment and other goodies he
has for sale: he's "for real", and the equipment is everything he purports
it to be. Jim Sanchez and I jointly ordered (and already received) the cards
and Ethernet software from Bob.
However, I'm posting this note so the "Ethernet naive" will realize what
is involved with these, and OTHER, cards for Ethernet. In other words,
this is a "caution" that you'll probably spend MORE on the needed Ethernet
accessories than the price of the "basic" card would suggest; this caveat is
true even if you're buying Ethernet cards for AT&T 6300, AT&T 6386, 3B2, and
other systems.
Consider this a mini Buyer's Guide but note that I am by NO stretch of any
imagination an Ethernet guru. I had the assistance of THE expert at H-P Labs
(Palo Alto) to help me determine and select the accessories I needed for my
installation to interconnect several 3B1, a Motorola 6300, and an Amiga to the
Ethernet; I'm still awaiting the arrival (expected within 48 hours) of the
additional accessories which I ordered Wednesday.
To connect a workstation or host to the 'net, the first accessory is what's
known as the "Ethernet card." Such cards exist for most computers (e.g. UNIX
boxes, IBM PCs and clones thereof, Macs, Amigas (the A2065 card), DEC VAXen,
DEC TOPS-20 systems, etc.). EVERY such card I've seen has (at least) a 15-pin
"D" AUI connector; many such cards also have a built-in transceiver with a
ThinNet BNC connector. The cards Bob is offering (AT&T WIN/3B LAN Interface
for the 3B1) have only the 15-pin AUI connector.
The 15-pin AUI connector permits YOU to select and choose the kind of Ethernet
backbone you want: standard (thick, stiff coax cable), ThinNet (RG-58 cable
with BNC connectors), Twisted Pair (e.g. StarLAN-like), Fiber Optic, Microwave,
etc. All of those ARE, in fact, IEEE 802.3 Ethernet compliant.
But to use the AUI connector, you need an AUI cable (with the "funny" D-15
connectors and slide latches and posts) to connect the Ethernet card to the
transceiver of your choice. And you need to select the Transceiver itself.
Transceivers are the actual attachment to the 'net. If you're using coax,
each transceiver will need a cable-TEE, and coax between transceivers, and
termination caps at each end of the coax per the following minimum config:
R--[T]-----(coax cable)--------[T]--R
[XVR] [XVR]
| |
| | <-- AUI cable
| |
[EC] [EC]
[WS] [WS]
where: "R" is a resistive 50-Ohm termination
"T" is a coax-TEE
"XVR" is a transceiver
"EC" is an Ethernet card
"WS" is your workstation or host
As stated, some "EC" have the "XVR & AUI cable" built-in; you'll still need
the cable-TEE, terminators and coax.
Depending on the manufacturer/vendor, ThinNet tranceivers range in cost from
$180 to $450. A 6-foot AUI cable costs $40-$50 each. RG-58 coax for ThinNet
is fairly inexpensive (e.g. 20' for $20, 100' for approx. $40, etc.)
For small Ethernet installations (2 to 4 workstations, max), some manufacturers
offer an integrated "box" having only AUI connectors. Some of these "boxes"
do have a built-in TEE, but many are closed-ended meaning you won't be able
to add more workstations in the future OR be able to connect to coax (or other)
backbone. Plan for your FUTURE needs before making any decisions unless you
have $$$ to burn. If you get such a "box" with a built-in TEE, you'll still
need to put the terminators on the TEE until you expand the network to either
other such boxes or to other transceivers.
Transceivers for "standard" Ethernet (the thick cable) cost either the same
or slightly more than the ones for ThinNet; the standard Ethernet transceivers
have the "vampire" tap that pierces the cable down to the center conductor
(and note you'll probably need a braid pick to poke around the cable).
Transceivers for fiber optic links are (presently) expensive and just were not
part of my consideration, but they may be for YOUR network.
So, per workstation, we're looking at these MINIMUM costs for ThinNet:
3B1 Ethernet card: $300 (Bob Slaski's offering price; you don't
AUI cable: 50 even want to know the original AT&T $$$)
Transceiver: 200
BNC TEE: 5
Terminators: 15
Coax: 20
------
$600 (rounded up)
NOW you can see why StarLAN and StarLAN-10 are so attractive, using the very
inexpensive twisted-pair wiring. StarLAN-10 is equivalent to the pending
10BaseT standard and IS an IEEE 802.3 Ethernet operating at 10Mbits/S. The
original StarLAN for the 3B1 is 802.3e-1988 1BASE5 (1Mbit/S). I'm not aware
of any StarLAN-10 accessories for the 3B1.
There are SO many accessories and other goodies one can put on the 'net that
you MUST get catalogs from the manufacturers to help make decisions.
One interesting transceiver unit seems to be from Fujikura in Atlanta, GA.
This unit was suggested by several people, but I haven't checked it out yet.
It apparently directly-connects to the D-15 on an Ethernet card thus obviating
the need of an AUI cable, and it has two BNC connectors built-in (thus having
the equivalent of a built-in TEE). Their number is (404) 956-7200 (and
(404)984-6965 for FAX)). No ideas as to price.
Black Box, of course, has a wide variety of goodies. They have a separate
LAN catalog with an incredible selection of Ethernet items; I simply cannot
type in the whole catalog. Suggest you contact them at:
ordering: 412/746-5530
tech info: 412/746-5565
Black Box has several "lines" of AUI cables, including a new one called their
"Office Ethernet Cable" which looks like a really good deal (esp. considering
the fragility of the D-15 connector on Ethernet cards).
Black Box ALSO has a (new product) 2- or 4-Port Direct Connect device(s) to
create an Ethernet LAN with NO external transceivers for up to 4 workstations;
this is a box that eliminates the need for coax for more-or-less closely
located systems and is, essentially, a "combination multiple transceiver and
backbone". They also have a wide variety of cables, separate transceivers,
bridges, repeaters, baluns and &tc. One MUST see the catalog to order any of
this stuff intelligently.
The prices from Black Box for thick, thin, fiber and twisted-pair Ethernet
devices appear quite competitive (after having checked other sources with
the help of my friend at H-P Labs), so I'd suggest contacting them as a
starting point. After evaluating the options available to ME, and considering
MY future needs, I ordered all my accessories from Black Box; I've dealt with
them many times in the past and have no complaints.
Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]