A couple of 5-4-3 refinements:
Try this picture:
MORE HOSTS
> \.../
> hosts HUB(s) hosts
> \|/ \|/ \|/
>host --- hub --- repeat --- SWITCH --- repeat-- hub --- hub---- etc...
> /|\ /|\ /|\
> hosts hosts hosts
>
The question of 'slot time' becomes confusing to me with the addition of
one, or more, switches into the (10,100,1000) circuit(s). The 'etc' above
asks, "What is the practical limit of cascaded switch/hub combinations in a
10 Mb/s ethernet? A combination 10 and 100 Mb/s ethernet? Yes, even with a
1Gb/s backbone?" Please, don't laugh, we here in K-12 education need to
lash up all kinds of stuff. Sometimes, if you can believe it, people will
even sneak an extra hub into the building!
No problem is insurmountable with the comparatively limitless private sector
resources. Network design is easy (easier) without the albatross of old
equipment never, ever, being surplused out, just moved out closer to the
edge. That's why we like the theory, as below. We frequently need to figure
out what flies ourselves.
Very best, G.
"Be strict in what you send, and forgiving in what you receive."
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
George Hartnell, Network Supervisor
Bellingham School District, 1306 DuPont St.
Bellingham, Wa. 98225-3198 (360)647-6860
[EMAIL PROTECTED] Internet Mail
-----Original Message-----
From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]]
Sent: Thursday, June 07, 2001 12:38 PM
To: [EMAIL PROTECTED]
Subject: Re: Rule 5-4-3 [7:7578]
At 02:17 PM 6/7/01, Aleksey Loginov wrote:
>Hi!
>Question about rule 5-4-3.
>How it's work for 10BaseT?
>This scheme correct?
>
> hosts hosts hosts
> \|/ \|/ \|/
>host --- hub --- repeat --- hub --- repeat --- hub --- host
> /|\ /|\ /|\
> hosts hosts hosts
>
Great job on the ASCII art! It's quite pleasing to the eye. ;-)
A 10BaseT hub is a repeater. Dare I say that there's no difference between
a Layer-1 repeater and a hub? Just like there's no difference between a
Layer-2 switch and a bridge, or a Layer-3 switch and a router. Argh.
One topology that became popular for explaining propagation delay on an
Ethernet network was the 5-4-3 topology. With a 5-4-3 topology, you can
have up to five segments in series, with up to four repeaters, and no more
than three mixing segments. If three mixing segments are used, then the
remaining two segments must be link segments. A mixing segment is one that
can have more than one attachment, such as a coax cable. A link segment is
a point-to-point link. It could be a fiber link between hubs, for example.
A 10BaseT hub connection to an end station is also a link segment.
The 5-4-3 topology is just one of many models that work actually. It is a
simplification of the actual rule that says that the round-trip propagation
delay in one collision domain must not exceed the time it takes a sender to
transmit 512 bits, which is 51.2 5s for 10-Mbps Ethernet, and is also known
as the slot time.
A single collision domain must be limited in size so that a station sending
a minimum-sized frame (64 bytes or 512 bits) can detect a collision and jam
signal reflecting back from the opposite side of the network, while the
station is still sending the frame. Otherwise, the station would be
finished sending and not listening for a collision, thus losing the
efficiency of Ethernet to detect a collision and quickly retransmit the
frame. For a higher layer to notice that the frame needs retransmitting
takes much more time. Ethernet retransmissions occur within nanoseconds.
Priscilla
>Any comments, please.
>
>Best regards,
>Aleksey
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=8036&t=7578
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