10Base5

10BASE5, also known as Thick Ethernet or Thicknet, is a historic Ethernet standard defined by IEEE 802.3 for baseband transmission at 10 megabits per second over a single thick coaxial cable. The designation combines the data rate (10 Mbps), the baseband signaling (BASE), and the maximum segment length (5 representing 500 meters).

Physical and topological characteristics

The main transmission medium is a single 50-ohm thick coaxial cable (such as RG-8) configured as a bus. A network segment can span up to 500 meters. Individual hosts connect to the main cable using vampire taps or drop cables, while terminators of 50 ohms are placed at each end of the bus to prevent signal reflections. The network operates under a shared medium where all stations can hear each other.

Access method and hardware

10BASE5 uses CSMA/CD for media access, with collisions detected by the transceivers. Hosts connect to the thick coax via a Thick Ethernet transceiver, which in turn connects to the host’s AUI (Attachment Unit Interface). The AUI provides the interface between the NIC and the external transceiver, which manages the electrical connection to the main cable and the required terminations.

Legacy and evolution

Introduced in the early 1980s as part of the original Ethernet family, 10BASE5 gave way to simpler and more scalable Ethernet variants, notably 10BASE-T (twisted pair) and later fiber options. The thicknet approach required specialized hardware and careful termination and was increasingly supplanted by easier-installation alternatives, leading to near-total obsolescence by the late 1990s to early 2000s. Today it is primarily of historical interest and seen in some museum or legacy-network contexts.