What is Ethernet? The Standard of Local Networking

Ethernet is a family of wired computer networking technologies commonly used in Local Area Networks (LAN), Metropolitan Area Networks (MAN), and even Wide Area Networks (WAN). Originally developed at Xerox PARC in 1976 by Robert Metcalfe, it has become the most widespread wired networking technology in the world due to its simplicity, low cost, and high performance.

Its success is largely due to standardization. The IEEE 802.3 working group is responsible for defining the physical and data link layer specifications for Ethernet. This ensures that devices from different manufacturers can communicate with each other seamlessly.

The Early Days: 10 Mbps Classic Ethernet

The first Ethernet standards operated at 10 Mbps and were based on a shared medium concept, where all devices were connected to a single communication line.

Coaxial Standards (Bus Topology)

• 10Base-5 (Thicknet): This was the original Ethernet standard. It used a thick, rigid coaxial cable as a shared backbone. Devices connected to the cable using "vampire taps" that pierced the insulation to make contact. The maximum segment length was 500 meters.
• 10Base-2 (Thinnet): A more affordable and flexible successor, using a thinner, more pliable coaxial cable. Devices were connected in a daisy-chain fashion using BNC T-connectors. The maximum segment length was 185 meters. Both of these standards created a single collision domain, meaning collisions were a normal part of operation, managed by the CSMA/CD protocol.

The Game Changer: 10Base-T (Star Topology)

The introduction of 10Base-T revolutionized networking by moving from a physical bus topology to a physical star. Instead of a single cable, each device was connected with its own cable to a central device.

• Medium: Utilized inexpensive Unshielded Twisted Pair (UTP) Category 3 or 5 cable with RJ-45 connectors.
• Central Device: Initially, devices were connected to a Hub. A hub acts as a simple multiport repeater, meaning it just copies incoming data to all other ports. Logically, the network still behaved like a bus, with all devices in the same collision domain. Later, hubs were replaced by much smarter switches.
• Benefits: This made networks much more reliable and easier to troubleshoot. A problem with one cable would only affect one device, not the entire network.

The Leap Forward: Fast Ethernet (100 Mbps)

As applications grew more demanding, the need for higher speeds led to the development of Fast Ethernet, standardized as IEEE 802.3u. This standard increased the speed tenfold to 100 Mbps.

• 100Base-TX: The dominant standard for Fast Ethernet over copper. It requires two pairs of wires in a Category 5 (or better) UTP cable. It became the de facto standard for LAN connections for many years.
• 100Base-FX: The fiber optic version of Fast Ethernet. It uses two strands of multimode fiber (one for transmitting, one for receiving) and is used for longer-distance connections, like linking floors in a building, up to 2 km.

A New Era: Gigabit Ethernet (1 Gbps)

The next tenfold increase in speed brought Gigabit Ethernet (1000 Mbps). This was a critical step, enabling high-performance server connections and network backbones.

Gigabit over Copper (1000Base-T)

Standardized as IEEE 802.3ab, 1000Base-T was a remarkable technological achievement. Instead of using only two pairs like Fast Ethernet, it uses all four pairs of a Category 5e (or better) cable to transmit simultaneously in both directions (full-duplex). This required complex signal processing and echo cancellation to work.

Gigabit over Fiber (1000Base-X)

Standardized as IEEE 802.3z, this family includes fiber optic versions for backbone connectivity:

• 1000Base-SX: Uses short-wavelength (S) lasers (around 850 nm) over multimode fiber, for distances up to 550 meters.
• 1000Base-LX: Uses long-wavelength (L) lasers (around 1310 nm) over both multimode (up to 550m) and single-mode fiber (up to 5 km, sometimes more).

From LAN to MAN/WAN: 10 Gigabit Ethernet and Beyond

With 10 Gigabit Ethernet (10 Gbps), Ethernet moved beyond the local area network and became a viable technology for metropolitan and wide area networks.

• 10GBASE-T: Provides 10 Gbps over copper, but requires high-quality Category 6A or Category 7 cable to reach the full 100-meter distance.
• 10GBASE-SR/LR/ER: A family of fiber standards for different distances: Short Reach (~300m on MMF), Long Reach (10km on SMF), and Extended Reach (40km on SMF).
• 10GBASE-LX4: An interesting standard that uses Coarse WDM (CWDM) to transmit four different wavelengths of light over a single pair of multimode fibers to achieve 10 Gbps.

Data Center and Carrier Speeds: 40 Gbps and 100 Gbps

Standardized in IEEE 802.3ba, speeds of 40 and 100 Gbps were achieved not by making a single lane run faster, but by combining multiple slower lanes in parallel. The part of the standard defining the physical connection is called the Physical Medium Dependent (PMD) sublayer.

Key Standards and Technologies

• 40GBASE-SR4 & 100GBASE-SR10: These are short-reach standards over parallel multimode fiber. 40G uses 4 lanes (fiber pairs) of 10 Gbps each. 100G uses 10 lanes of 10 Gbps each.
• 40GBASE-LR4 & 100GBASE-LR4: These are long-reach standards over a single pair of single-mode fibers. Instead of parallel fibers, they use Wavelength Division Multiplexing (WDM) to transmit 4 separate wavelengths ("colors") down the fiber. For 40G, each wavelength carries 10 Gbps. For 100G, each wavelength carries 25 Gbps.
• 100GBASE-ER4: An extended-reach version of LR4, capable of transmitting 100 Gbps up to 40 km over single-mode fiber, blurring the lines between LAN and carrier-grade transport technologies.

The evolution continues, with standards now defined for 400 Gbps, 800 Gbps, and even Terabit Ethernet, consistently proving Ethernet's remarkable adaptability and longevity.