10BASE5 (also known as thick Ethernet or thicknet) was the first commercially-available variant of Ethernet. 10BASE5 uses a thick and stiff coaxial cable up to 500 metres (1,600 ft) in length. Up to 100 stations can be connected to the cable using vampire taps and share a single collision domain with 10 Mbit/s of bandwidth shared among them. The system is difficult to install and maintain.
10BASE5 was superseded by much cheaper and more convenient alternatives: first by 10BASE2 based on a thinner coaxial cable, and then once Ethernet over twisted pair was developed, by 10BASE-T and its successors 100BASE-TX and 1000BASE-T. As of 2003, IEEE 802.3 has deprecated this standard for new installations.
The name 10BASE5 is derived from several characteristics of the physical medium. The 10 refers to its transmission speed of 10 Mbit/s. The BASE is short for baseband signalling (as opposed to broadband), and the 5 stands for the maximum segment length of 500 metres (1,600 ft).
Network design and installation
For its physical layer 10BASE5 uses cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, 0.375-inch (9.5 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 metres (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 spike is forced to pierce and contact the inner conductor while other spikes bite into the outer braided shield. Precise special tools and careful skill are required to install a reliable and durable tap. 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-metre intervals. This distance was chosen to not correspond to the wavelength of the signal; 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.
As a transmission line, a 10BASE5 segment must be terminated with an impedance-matched current sink at each end. For coaxial-cable-based Ethernet, each end of the cable has a 50 ohm termination resistor attached, which receives the signal energy and dissipates the energy as heat. Typically this resistor is built into a male N connector and attached to the female-terminated end of the cable just past the last device. With a termination missing, or if there is a break in the cable, the energy of the signal on the bus will be reflected back down the cable, rather than being dissipated. This reflected signal amounts to a second signal present on the cable, which is indistinguishable from a collision, thus preventing communication of all nodes along the entire segment.
The logical simplicity of tapping new nodes onto the in-place network cable is complicated by the on-site craftsmanship required to successfully install a tap, and the dire consequences of a mishap during installation. Tap points frequently lie in inconvenient locations, such as in a cramped ceiling space, much like the plumbing or car-repair problem of the hardest physical tasks being required in the worst possible places.
The promiscuous logistic of the tapping design creates a delicate situation where one faulty tap prevents the entire network segment from working, yet the failure symptoms do not isolate which tap (which can number up to 200 in quantity) is faulty. In the worst cases, a faulty tapping procedure could inadvertently damage the cable beyond repair, requiring a costly replacement of the entire segment; or more than one tap could fail, making efficient repair by trial-replacement of taps one at a time impossible. Tap faults could also be latent, appearing long after taps had been installed, and giving no suggestion of which most-recently-installed tap was suspect.
The thick cable is mechanically stiff and difficult to bend around tight corners, handle in closets and plenums, or fish through conduits.
The subsequent 10BASE2 redesign solved these severe problems of diagnosing and repairing 10BASE5, by changing the cabling topology to a series of factory-made, shorter, individual, connectorized pieces which could be quickly disconnected, reconfigured, and replaced.
|Wikimedia Commons has media related to 10BASE5.|
- IEEE 802.3-2005 8. Medium attachment unit and baseband medium specifications, type 10BASE5
- Stallings, William (1993). Local and Metropolitan Area Networks. Macmillan Publishing Company. p. 107. ISBN 0-02-415465-2.
- All-in-One Networking+ Certification Exam Guide, Mike Meyers, 3rd Ed., McGraw-Hill, 2004, p. 79.
- "5-4-3 rule". Retrieved 2010-06-30.
- sponsor Technical Committee on Computer Communications of the IEEE Computer Society. (1985). IEEE Standard 802.3-1985. IEEE. p. 121. ISBN 0-471-82749-5.
- Urd Von Burg; Martin Kenny (December 2003). "Sponsors, Communities, and Standards: Ethernet vs. Token Ring in the Local Area Networking Business" (PDF). Archived (PDF) from the original on 2012-03-21.