mshiels@tmsoft.uucp (Michael A. Shiels) (01/23/91)
I know the cabling limitations with Thick/Thin ethernet. 500M and 185M respectively. BUT I AM IN NEED OF REPEATER LIMITATIONS! I have gotten 2 or 3 different references. DEC says no more than 2 repeaters between nodes. Black Box says no more than 2 inter repeater links which I would take to mean 3 repeaters with 2 links between the three? Any others out there?
koning@koning.enet.dec.com (Paul Koning) (01/26/91)
|> |>I know the cabling limitations with Thick/Thin ethernet. 500M and 185M |>respectively. BUT I AM IN NEED OF REPEATER LIMITATIONS! |> |>I have gotten 2 or 3 different references. DEC says no more than 2 repeaters |>between nodes. Black Box says no more than 2 inter repeater links which I |>would take to mean 3 repeaters with 2 links between the three? Any others |>out there? |> Unfortunately, the SAME rules are described by different terminology in different places. That doesn't change the rules themselves, though. I'd suggest you get the IEEE 802.3 standard and the DEC/Intel/Xerox "Blue Book" (Ethernet spec). Those are the actual authority. If you read them side by side you will see that in fact they describe the same rules, but by different words... When DEC mentions the "two repeater" rule, that means two local repeaters. There are also fiber repeaters, with an inter-repeater link between them; the traditional term for those is "half-repeaters". A pair of those with its inter-repeater link counts for one repeater. The IEEE 802.3 spec calls each half-repeater a "repeater set". It then gives a maximum of 5 segments, of which at most 3 can be coax segments, and 4 repeater sets. So therefore: a. If you have fiber repeaters ("half-repeaters") you're allowed four of those; 3 coax segments, and 2 inter-repeater links. You're at the limit for all 3 limits simultaneously. b. If you have only local repeaters, you're allowed two. What limits you here is the rule that you can have at most 3 coax segments. Again, the problem is differences in wording, NOT differences in the actual rules. If you care to go through the effort, it's instructive to draw several configurations, both legal and illegal ones, and see why each one of them does (or does not) meet each of the possible restatements of the rules... paul
ted@blia.sharebase.com (Ted Marshall) (01/26/91)
In article <1991Jan23.050705.5029@tmsoft.uucp>, mshiels@tmsoft.uucp (Michael A. Shiels) writes: > I have gotten 2 or 3 different references. DEC says no more than 2 repeaters > between nodes. Black Box says no more than 2 inter repeater links which I > would take to mean 3 repeaters with 2 links between the three? Any others > out there? Both DEC and Black-Box are saying the same thing. By "inter-repeater link", they mean a point-to-point link (generally fiber) between half-repeater (otherwise called remote-repeater) pairs. The general rule is that no pair of stations can be separated by more than two repeaters. You may substitute 2 half-repeaters connected by fiber for one or each of those. Hope this clears it up. -- Ted Marshall ted@airplane.sharebase.com ShareBase Corp., 14600 Winchester Blvd, Los Gatos, Ca 95030 (408)378-7000 The opinions expressed above are those of the poster and not his employer.
network@zeus.unomaha.edu (01/27/91)
In article <19450@shlump.nac.dec.com>, koning@koning.enet.dec.com (Paul Koning) writes: > > The IEEE 802.3 spec calls each half-repeater a "repeater set". It then > gives a maximum of 5 segments, of which at most 3 can be coax segments, > and 4 repeater sets. So therefore: > > b. If you have only local repeaters, you're allowed two. What limits you > here is the rule that you can have at most 3 coax segments. This of course assumes you don't have a multi-port repeater. Also you can place a bridge in between repeater link your sets of two repeaters to get around this problem. Paul is quite correct about most fiber repeaters being half repeaters. Steven Lendt Network Manager University of Nebraska at Omaha Internet: Network@Zeus.UNOmaha.EDU Bitnet: Network@UNOMA1
phil@dgbt.doc.ca (Phil Blanchfield DGBT/DIP) (01/30/91)
In article <7160.27a20db7@zeus.unomaha.edu> network@zeus.unomaha.edu writes: >In article <19450@shlump.nac.dec.com>, koning@koning.enet.dec.com (Paul Koning) writes: >> >> The IEEE 802.3 spec calls each half-repeater a "repeater set". It then >> gives a maximum of 5 segments, of which at most 3 can be coax segments, >> and 4 repeater sets. So therefore: >> >> b. If you have only local repeaters, you're allowed two. What limits you >> here is the rule that you can have at most 3 coax segments. >This of course assumes you don't have a multi-port repeater. Also you >can place a bridge in between repeater link your sets of two repeaters >to get around this problem. >Paul is quite correct about most fiber repeaters being half repeaters. Does anyone know how a 10baseT concentrator fits in here? Our site is just bringing up an Optical Data Systems 10BaseT network and I have recently attached our old Thicknet segment to a concentrator box. This box is then connected via fiber to another box in another building. Several stations on this second concentrator access systems on the Thicknet. Would these newfangled 10BaseT boxes count as a half-repeater or a full repeater? -- Phil Blanchfield The Communications Research Centre 3701 Carling Avenue, Ottawa Ontario CANADA Internet: phil@dgbt.doc.ca OR phil@dgbt.crc.dnd.ca
pat@hprnd.rose.hp.com (Pat Thaler) (02/06/91)
The term half-repeater is really a misnomer. A coax-to-coax repeater
has the same functionality and delay as a coax-to-fiber repeater.
There is nothing "half" about the coax-to-fiber repeater. What is
different is the delays of the different MAU types and effect of
the media on delays, particularly delays in detecting start and
end of collision. Collision detect occurs significantly faster
on link segments (Fiber Optic Inter-repeater Link (FOIRL) and
10BASE-T) than on coax segments (10BASE2 and 10BASE5).
So, there is sufficient delay budget for a maximum path between any
two stations on the network of (condensed from IEEE 802.3 Section 13):
4 Repeaters
5 Segments
At most 3 of those segments may be coax
The remainder may be link segments of up to 500 m each.
10BASE-T and FOIRL repeaters are often called "hubs" or "concentrators"
because of their position at the hub of star configured wiring.
You could have a backbone of 3 coax segments connected
by two repeaters and attach repeaters connecting 10BASE-T segments
to the backbone. This configuration obeys the rules above.
Counting coax-to-link-segment repeaters to be half-repeaters breaks
down in this example. You would count 2 repeaters plus 2 half-repeaters
equals 3 repeaters; one too many by the "half-repeater rules." Yet
you would have a legal configuration.
Pat Thaler