Ethernet

Ethernet is a wired networking standard (IEEE 802.3) that connects devices to a router or switch via cable. It is full-duplex (send and receive simultaneously), not subject to radio interference, and delivers consistent throughput and low latency. For speed-sensitive tasks, Ethernet outperforms Wi-Fi in every measurable way.

Ethernet standards timeline

How Ethernet frames work

Data on an Ethernet network travels in frames. Each frame has a fixed structure: a preamble (7 bytes) that synchronises the receiver's clock, a start frame delimiter (1 byte), a destination MAC address (6 bytes), a source MAC address (6 bytes), an optional 802.1Q VLAN tag (4 bytes), an EtherType/length field (2 bytes), the payload (46–1500 bytes for standard frames, up to 9000 bytes for jumbo frames), and a Frame Check Sequence (FCS) (4 bytes) — a CRC checksum that allows the receiver to detect transmission errors. If the FCS does not match, the frame is silently discarded and upper-layer protocols (TCP) handle retransmission. The maximum payload of 1500 bytes is the standard MTU (Maximum Transmission Unit) used on virtually all internet connections.

CSMA/CD and why modern Ethernet has no collisions

Early Ethernet used CSMA/CD (Carrier Sense Multiple Access with Collision Detection) — a shared-bus protocol where all devices competed for the same wire. If two devices transmitted simultaneously, a collision occurred, both backed off for a random period, and retransmitted. This half-duplex architecture severely limited throughput on busy networks. Modern Ethernet uses network switches that give each device a dedicated point-to-point link to the switch port. With a dedicated link, there is no shared medium and no possibility of collision. Every modern switched Ethernet connection operates in full-duplex mode — the device can send and receive simultaneously at full link speed. CSMA/CD is entirely irrelevant on switched networks and exists only in standards documents for legacy compatibility.

Cable categories

• Cat5e — supports up to 1 Gbps at 100 m; adequate for gigabit plans; most existing home wiring is Cat5e
• Cat6 — supports 1 Gbps at 100 m and 10 Gbps at 55 m; tighter twist, better crosstalk rejection; recommended for new installations
• Cat6A — supports 10 Gbps at full 100 m; required for multi-gig plans above 2.5 Gbps over long runs; thicker and less flexible than Cat6
• Cat8 — supports 25–40 Gbps at up to 30 m; designed for data centre top-of-rack connections; no practical benefit in homes

The 100 m (328 ft) maximum segment length applies to all copper Ethernet standards. Runs longer than 100 m require a switch or repeater to maintain signal integrity. For home installations, this limit is rarely reached.

Power over Ethernet (PoE)

PoE (Power over Ethernet) delivers electrical power alongside data over the same Cat5e/Cat6 cable, eliminating the need for a separate power adapter at the remote device. PoE (IEEE 802.3af) delivers up to 15.4 W per port. PoE+ (802.3at) delivers up to 30 W. PoE++ (802.3bt) delivers up to 60 W (Type 3) or 100 W (Type 4). Common PoE-powered devices include IP cameras, Wi-Fi access points, VoIP phones, and small switches. PoE requires a PoE-capable switch or injector at the source end; the powered device must also support PoE or be connected via a PoE splitter.

Auto-negotiation and duplex mismatch

Auto-negotiation is the process by which two connected Ethernet devices agree on the highest common speed and duplex mode. Both ends advertise their capabilities, and the link comes up at the best mutually supported settings. Problems arise when one side has auto-negotiation disabled and is hard-coded to a specific speed/duplex. If one end is set to 100 Mbps full-duplex and the other auto-negotiates, the auto-negotiating side will fall back to half-duplex (since it detects a link but cannot negotiate) — a duplex mismatch. This causes severe throughput degradation and high error counts without obvious failure. The fix is to ensure both ends are either both set to auto-negotiate, or both hard-coded to the same speed and duplex.

Ethernet vs Wi-Fi trade-offs

• Throughput: Wired Gigabit Ethernet delivers 920–960 Mbps consistently. Wi-Fi 6 at close range delivers 600–800 Mbps; performance drops significantly with distance and obstacles.
• Latency: Ethernet adds 0.1–0.3 ms of switching latency. Wi-Fi adds 1–5 ms of radio access delay, plus variable queuing delay under load.
• Reliability: Ethernet is unaffected by neighbouring networks, microwave ovens, cordless phones, or building materials. Wi-Fi performance is highly environment-dependent.
• Convenience: Wi-Fi requires no cable runs. Ethernet requires physical installation but is permanently reliable once installed.

For gaming, video calls, and any task where consistent low latency matters, Ethernet is strongly preferable. For mobile devices and casual browsing, Wi-Fi is sufficient.

Frequently Asked Questions

What Ethernet cable do I need for gigabit internet?

Cat5e is the minimum for 1 Gbps and works fine. Cat6 is the recommended standard for new installations. Cat6A is only needed if you plan to run 2.5 Gbps or 10 Gbps connections, or if cable runs exceed 55 meters.

How much faster is Ethernet than Wi-Fi?

On a 1 Gbps plan: a wired connection typically delivers 920–960 Mbps; Wi-Fi 6 delivers 600–800 Mbps close to the router; Wi-Fi 5 delivers 400–600 Mbps. The difference grows with distance and walls between device and router.