55
Appendix C
IEEE 802.3 Quick Primer
10BASE-T
10BASE-T UTP media was implemented to reduce Ethernet wiring costs.
UTP wiring is installed in most buildings for telephone systems. Care must
be taken to ensure that the UTP wiring used for 10BASE-T is able to carry
the high Ethernet data rates before a 10BASE-T network solution is
implemented.
Unlike coaxial Ethernet, 10BASE2 and 10BASE5, 10BASE-T UTP is
point-to-point wiring. Typically, one end is connected to an Ethernet
10BASE-T NIC or transceiver (MAU) and the other end is connected to a
10BASE-T hub (repeater). Straight-through cabling pin-out is used for
hub-to-MAU connections. Hub-to-hub and MAU-to-MAU connections are
allowed using a UTP cable with a cross-over function crossing TD+ and TD-
with RD+ and RD- signals. No other attachments are allowed along the
length of the UTP wire; however, wiring patch panels and punch-down blocks
is allowed for interconnecting segments. The cable should be at least Level
3 UTP, 100
Ω
impedance, 22 to 26 AWG, and should not exceed 100 meters
(328 ft.) in length from one end to the other. See Table 5 in Appendix A for
comparison of different UTP cables.
Four-Repeater Rule
Up to four repeater/hub units may be connected, for a total of five segments,
provided that two of the segments are link segments. Link segments (such as
fiber) have no MAU attachments. If all segments are coax segments having
MAU attachments, a maximum of two repeater/hub units and three segments
is allowed.
