Specifications

RADring
Installation & Operation Manual Ethernet Design Considerations
3/11/98 12:25 Ethernet Physical Design 7-3
7.2 Ethernet Physical Design
Design Methods
When determining the physical feasibility of your Ethernet Network, there
are two basic limitations that have to be taken into account:
•
Distance limitations
•
Repeater count limitations.
Any configuration is allowed if it meets the Repeater count limitations and
the Distance limitations. When only electrical modules are used, when the
repeater count limitation is met, the distance limitation is met automatically.
The reason for that is the relatively short allowed cable length of the
electrical modules (100m). When using fiber optic modules the design must
met both limitations and the designer must check carefully the network
components delays.
Design Rules -
Basics
Distance
The distance between any two nodes of the same segment must not be
greater than 28.8µsec. This limitation promises that collision will be detected
during transmission of the shortest frame. The 28.8µsec includes the cable
propagation delay as well as the other components like transceivers,
repeaters, etc. delay
Note that the network efficiency is getting lower when the segment (the
maximum distance between any two stations) become longer. The reason for
that is that the probability for collision is greater for longer segments.
Repeater Count
Number of repeaters between any two stations of the same segment must
not be greater than four. This limitation promises minimum gap between two
packets while arriving their destination.
Overcoming Repeater Count Limitations
Every RADring hub containing Ethernet cards acts as one Ethernet multi port
repeater. The repeaters (hubs) are connected via IRL (Inter Repeater Link)
connections. The repeater count limitation can be kept in two ways: The first
way can be chosen mainly during the LAN design phase and the second way
can be chosen any time.
First Way: Design the network in STAR topology as much as it can be done.
In this kind of topology the number of repeaters between each two stations
will become minimal: The first figure shows prohibited connection in which
there are more than five repeaters between station A and station B. The
second figure shows the recommended topology in which more stations can
be connected to one Ethernet segment without being connected through
more than 4 repeaters.