Hardware Reference
In-Depth Information
networks still use twisted-pair Ethernet cabling. Occasionally you might still find some based on
Thick or Thin Ethernet coaxial cable.
Thick and Thin Ethernet Coaxial Cable
The first versions of Ethernet were based on coaxial cable. The original form of Ethernet, 10BASE-5,
used a thick coaxial cable (called
Thicknet
) that was not directly attached to the NIC. A device
called an
attachment unit interface (AUI)
ran from a DB-15 connector on the rear of the NIC to the
cable. The cable had a hole drilled into it to allow the “vampire tap” to be connected to the cable.
NICs designed for use with thick Ethernet cable are almost impossible to find as new hardware
today.
10BASE-2 Ethernet cards use a BNC (Bayonet-Neill-Concelman) connector on the rear of the NIC.
Although the thin coaxial cable (called
Thinnet
or
RG-58
) used with 10BASE-2 Ethernet has a
bayonet connector that can physically attach to the BNC connector on the card, this configuration is
incorrect and won't work. Instead, a BNC T-connector attaches to the rear of the card, allowing a
Thin Ethernet cable to be connected to either both ends of the T (for a computer in the middle of the
network) or to one end only (for a computer at the end of the network). A 50-ohm terminator is
connected to the other arm of the T to indicate the end of the network and prevent erroneous signals
from being sent to other clients on the network. Some early Ethernet cards were designed to handle
thick (AUI/DB-15), thin (RG-58), and UTP (unshielded twisted pair) cables. Combo cards with both
BNC and 8P8C (RJ-45) connectors are still available on the surplus equipment market but can run at
only standard 10Mbps Ethernet speeds.
Figure 17.5
compares Ethernet DB-15 to AUI, BNC coaxial T-connector, and 8P8C (RJ-45) UTP
connectors, and
Figure 17.6
illustrates the design of coaxial cable.
Figure 17.5. An Ethernet network card with Thick Ethernet (DB-15), Thin Ethernet (RG-58
with T-connector), and UTP (8P8C/RJ-45) connectors.
