Ethernet physical layer
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| A standard 8P8C (often called RJ45) connector used most commonly on cat5 cable, one of the types of cabling used in Ethernet networks | |
| Standard | IEEE 802.3 (2002 onwards) |
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| Physical media | Coaxial cable, twisted pair, optical fiber |
| Network topology | Point-to-point, star, bus |
| Major variants | 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX, 1000BASE-LX10 |
| Maximum distance | 100 metres (328 ft) over twisted pair, up to 100 km over optical fiber |
| Mode of operation | Differential (Balanced) |
| Maximum bit rate | 1 Mbit/s to 100 Gbit/s |
| Voltage levels | ± 2.5V (over twisted pair) |
| Available signals | Tx+, Tx−, Rx+, Rx− |
| Common connector types | 8P8C, LC, SC, ST |
The Ethernet physical layer is the physical layer component of the Ethernet family of computer network standards which defines the electrical or optical properties of the physical connection between a device and the network or between network devices.
The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 1 Mbit/s to 100 Gbit/s, while the physical medium can range from bulky coaxial cable to twisted pair and optical fiber. In general, network software will work similarly on all physical layers.
10 Gigabit Ethernet was already used in both enterprise and carrier networks by 2007, with 40 Gbit/s and 100 Gigabit Ethernet ratified. Higher speeds are under development.Robert Metcalfe, one of the co-inventors of Ethernet, in 2008 said he believed commercial applications using Terabit Ethernet may occur by 2015, though it might require new Ethernet standards.
Many Ethernet adapters and switch ports support multiple speeds, using autonegotiation to set the speed and duplex for the best values supported by both connected devices. While this can practically be taken for granted for ports supporting twisted-pair cabling, only few optical-fiber ports support multiple speeds. If auto-negotiation fails, some multiple-speed devices sense the speed used by their partner, but will assume half-duplex. A 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T.
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