Wired Communication
Operations for Ethernet and Wi-Fi networks differ primarily at the Physical and Data Link layers. IEEE 802.3 protocol standards govern wired connections, supporting speeds from 10 Mbps up to 400 Gbps, and use CSMA/CD on hubs for collision management.
Evolution of Wired Networks
Wired networking has evolved over more than a century, from analogue telephone signals to multi-hundred-gigabit Ethernet links. The timeline below captures the key milestones that shaped modern wired infrastructure.
| Year | Milestone |
|---|---|
| 1876 | Invention of the telephone — the first electrical voice-communication system. |
| 1964 | Introduction of optical fibre demonstrated the potential of light-based wired networks. |
| 1970 | Ethernet technology developed using coaxial or twisted copper cabling. |
| 1980 | The decade built the foundation for DSL (Digital Subscriber Line) broadband. |
| 2000 | Broadband technology becomes widely available to consumers and businesses. |
Professor Messer. (2018). Introduction to Ethernet — CompTIA Network+ N10-007 — 1.3. YouTube. https://youtu.be/iXfBbs9SSFQ
Difference Between Hub, Switch, and Router
Understanding the distinctions between these three core intermediary devices is essential for designing and troubleshooting any Ethernet network.
Ethernet hubs are legacy devices that operate mainly on Layer 1 (the Physical Layer). They use half-duplex communication — data travels in only one direction at a time.
Hubs implement CSMA/CD by comparing transmitted data with received data, or by recognising that signal amplitude is higher than normal on the medium. A back-off algorithm manages retransmission after collisions.
Because a hub forwards every Ethernet frame to all ports except the sender's, connecting a packet analyser to the hub allows all traffic on the segment to be monitored.
Switches maintain a table of MAC addresses and associated ports (the Content Addressable Memory / CAM table), forwarding frames only to the correct destination port.
- Operate in full duplex (except when connected to a hub); therefore do not use CSMA/CD.
- Do not interact with Layer 3 and above — unlike routers — unless it is a Layer 3 switch.
- A Layer 3 switch combines switch and router functionality: supports static and dynamic IP routing, and VLAN intelligence.
A switch has a finite CAM table. Attackers can flood the switch with spoofed MAC addresses, exhausting the table and forcing the switch to broadcast all frames — similar to a hub.
Routers always connect different networks (WANs), unlike switches which connect end devices on the same network. They use routing protocols to exchange route information, compare paths, and select the best path to a destination network.
Common Routing Protocols
- OSPF — Open Shortest Path First
- BGP — Border Gateway Protocol
- IP — Internet Protocol (IPv4 / IPv6) for delivering messages across multiple networks
| Feature | Hub | Switch | Router |
|---|---|---|---|
| OSI Layer | Layer 1 | Layer 2 (or 3) | Layer 3 |
| Addressing | None | MAC address | IP address |
| Duplex mode | Half duplex | Full duplex | Full duplex |
| CSMA/CD | Yes | No | No |
| Collision domain | Single shared domain | Per-port domain | Per-port domain |
| Connects | Same network | Same network | Different networks |
| Status | Legacy | Current standard | Current standard |
Handling Collisions & Errors
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
CSMA/CD is the access method used by Ethernet hubs to manage shared media. It has three distinct phases:
Listen before transmitting — the station must hear silence on the medium before sending.
If two or more stations both hear silence, they may begin transmitting simultaneously.
If two or more stations transmit concurrently, a collision is detected by the NIC. All stations must stop and retransmit after a random back-off period.
Reducing collisions: CSMA/CD inherently introduces collisions on shared media. Subnetting a large network reduces the collision domain size and therefore the collision rate.
Collision domains & switches: A collision domain is the network segment where collisions can occur. Switches eliminate collisions by operating in full duplex and forwarding frames one at a time to the correct destination port — giving each port its own dedicated channel between transmitter and receiver.
Ethernet error handling: Ethernet performs error detection via a checksum (FCS) in each frame. Damaged frames are silently discarded — there is no built-in acknowledgement of delivery, similar to postal mail. Reliable delivery requires additional protocols: for example, TCP (Layer 4) can be encapsulated in the frame payload to provide handshakes, delivery receipts, and retransmission logic.
Modern switched networks use full-duplex links, meaning CSMA/CD is not needed. CSMA/CD is only relevant on legacy half-duplex hub-based segments.
Key Takeaways
- IEEE
802.3is the standard for wired Ethernet (10 Mbps – 400 Gbps). - Hubs = Layer 1, half duplex, shared collision domain, CSMA/CD required.
- Switches = Layer 2, full duplex, per-port collision domain, no CSMA/CD.
- Routers = Layer 3, connect separate networks, use routing protocols (OSPF, BGP).
- Ethernet error detection uses FCS; reliable delivery depends on upper-layer protocols (e.g. TCP).