10BASE5

The physical layer

Cabling and Connectors

For its physical layer, 10BASE5 uses cable similar to RG-8/U coaxial cable but with extra braided shield. This is a stiff, 0.4-inch (10 mm) diameter cable with an impedance of 50 ohms, a solid center conductor, a foam insulating filler, a shielding braid, and an outer jacket. The outer jacket is often yellow-to-orange fluorinated ethylene propylene (for fire resistance) so it often is called yellow cable, orange hose, or sometimes humorously frozen yellow garden hose. 10BASE5 coaxial cables had a maximum length of 500 meters (1,600 ft). Up to 100 nodes could be connected to a 10BASE5 segment.

Transceiver nodes can be connected to cable segments with N connectors, or via a vampire tap, which allows new nodes to be added while existing connections are live. A vampire tap clamps onto the cable, a hole is drilled through the outer shielding, and a spike is forced to pierce the outer three layers and contact the inner conductor while other spikes bite into the outer braided shield. Care is required to keep the outer shield from touching the spike; installation kits include a coring tool to drill through the outer layers and a braid pick to clear stray pieces of the outer shield.

Transceivers should be installed only at precise 2.5-meter intervals. This distance was chosen to not correspond to the signal's wavelength; this ensures that the reflections from multiple taps are not in phase. These suitable points are marked on the cable with black bands. The cable is required to be one continuous run; T-connections are not allowed.

Electrical Termination

As is the case with most other high-speed buses, segments must be terminated at each end. For coaxial-cable-based Ethernet, each end of the cable has a 50 ohm resistor attached. Typically, this resistor is built into a male N connector and attached to the cable's end just past the last device. With termination missing, or if there is a break in the cable, the signal on the bus will be reflected, rather than dissipated when it reaches the end. This reflected signal is indistinguishable from a collision and prevents communication.

Signaling

Disadvantages

Stations are connected to the cable using vampire taps. This complicates adding new stations to the network because of the need to pierce the cable accurately. The cable is stiff and difficult to bend around corners. One improper connection can take down the whole network and finding the source of the trouble is difficult.

This type of network was potentially more expensive to install and maintain than networks based on twisted pair cabling, since the latter might have already been present in sufficient quality as the phone network in office buildings.