Installation manual

IEEE 802.3 Quick Primer
54
10BASE2 (Thin) Ethernet
When configuring thin coax segments, IEEE 802.3 specifications allow up
to 30 MAU attachments per cable segment, spaced at no less than 0.5
meters (1.64 ft.). The 10BASE2 cable length cannot exceed 185 meters
(606 ft.) per segment. The worst-case propagation delay for a 185 meter
(606 ft.) thin Ethernet segment is 950.9 ns. The propagation delay for thin
(10BASE2) Ethernet cable is 5.14 ns/meter. Both ends of the segment
must be terminated with a 50 Ω termination with a power rating of 0.5
watts or greater. The segment shield must be earth grounded at only one
point on the cable.
10BASE5 (Thick) Ethernet
When configuring 10BASE5 coax segments, IEEE 802.3 specifications
allow 100 MAU attachments or less, spaced at multiples of 2.5 meters (8.2
ft.) measured accurately from the cable end (50 Ω terminator included).
The 10BASE5 cable segment cannot exceed 500 meters (1640 ft.) in
length. Worst-case end-to-end propagation delay of a 10BASE5 coax
segment is 2165 ns. Propagation delay of 10BASE5 Ethernet coax is
calculated at 4.33 ns/meter. Both ends of the segment must be terminated
with a 50 Ω termination with a power rating of 0.5 watts or greater. Earth
grounding of the segment shield must take place at only one point on the
cable.
AUI Drop Cables AUI or Drop cables can be no longer than 50 meters (164 ft.) each.
Attachments may be made only to the cable ends at the 15-pin D-shell
connector. AUI Drop cables may have a maximum 257 ns propagation
delay, as used for computing the worst-case propagation delay of a cable
system. AUI cable propagation delay is approximately 5.13 ns/meter.
Internally, this cable consists of four shielded twisted-pair wires with an
overall shield and drain wire; there is a 15-pin D-shell male connector at
one end and a 15-pin D-shell female connector at the other end. Cable
impedance is nominally 78 Ω. The AUI cable typically connects a
transceiver attached to a coaxial segment with a DTE (workstation).
Propagation
Propagation delay is the time it takes a signal to travel from the input of a
system component to the output; it is usually measured in nanoseconds.
IEEE 802.3 has specific propagation delay maximums for the Ethernet
components. Cable length plays a major role; i.e., a 50 meters (164 ft.) AUI
cable has a maximum propagation delay of 257 ns. The propagation delay
of cable depends on the length and velocity factor of the cable type.
Round-trip propagation delay throughout the entire cable system, from
farthest ends, may not exceed 51.7 µs, ± 4 µs.