1.5 Compare and contrast transmission media and transceivers
Wired Media
📘CompTIA Network+ (N10-009)
Wired Media: 802.3 Standards (Ethernet)
The 802.3 standard is a set of rules developed by IEEE for wired Ethernet networks. It defines how devices communicate over cables and how data is transmitted in a network. It is the most widely used wired networking standard in IT environments.
Think of it as a “rulebook” for Ethernet connections in offices, data centers, and network closets.
1. Basics of 802.3 Ethernet
- Purpose: To allow devices (computers, servers, switches) to send data to each other reliably over cables.
- Media types: Mostly uses twisted-pair copper cables (like Cat5e, Cat6, Cat6a) or fiber optic cables.
- Data framing: Ethernet defines how data is packaged into frames for transmission. A frame includes:
- Source and destination addresses
- Error-checking information
- Payload (actual data)
2. Speed and Cabling Variants
802.3 defines multiple Ethernet speeds and the types of cabling each uses. Here’s a simplified table for exam purposes:
| Standard | Speed | Max Cable Length | Cable Type | Notes |
|---|---|---|---|---|
| 10BASE-T | 10 Mbps | 100 meters | Cat3 or better | Original Ethernet over twisted-pair copper |
| 100BASE-TX | 100 Mbps | 100 meters | Cat5 | Fast Ethernet |
| 1000BASE-T | 1 Gbps | 100 meters | Cat5e/Cat6 | Gigabit Ethernet over copper |
| 10GBASE-T | 10 Gbps | 100 meters | Cat6a or Cat7 | 10 Gigabit over copper |
| 1000BASE-SX | 1 Gbps | ~550 meters | Multimode fiber | Short-range fiber connections |
| 1000BASE-LX | 1 Gbps | 5 km | Single-mode fiber | Long-range fiber |
| 10GBASE-SR | 10 Gbps | 300 meters | Multimode fiber | Short-range 10G |
| 10GBASE-LR | 10 Gbps | 10 km | Single-mode fiber | Long-range 10G |
Key Exam Points:
- “BASE” = Baseband (signals use the entire cable for one signal at a time)
- Copper Ethernet has a max 100 m length for twisted-pair cables
- Fiber Ethernet can go long distances, up to several kilometers
- Different standards suit different environments (data centers often use fiber, offices use copper)
3. Duplex and Collision Handling
- Half-duplex: Devices can send or receive, but not at the same time. Older Ethernet like 10BASE-T used this.
- Full-duplex: Devices can send and receive simultaneously. Modern Ethernet (1 Gbps and above) uses full-duplex.
- Collision domains: In half-duplex, if two devices send data at the same time, a collision occurs. Switches and full-duplex remove this problem.
4. Frame Size
- Standard Ethernet frame: 64 bytes minimum, 1518 bytes maximum (without VLAN tags)
- Larger frames (jumbo frames) can be used in high-performance networks like data centers
- Frames include:
- Preamble (sync data)
- Destination MAC address
- Source MAC address
- EtherType (protocol type)
- Data payload
- CRC (error checking)
5. Auto-Negotiation
- Modern 802.3 devices can automatically agree on speed and duplex.
- Example: A switch port can detect if a connected device supports 1 Gbps full-duplex and adjust automatically.
- Important for exam: Auto-negotiation prevents mismatched speed/duplex, which can cause network slowness.
6. Common IT Environment Usage
- Offices:
- Use 100BASE-TX or 1000BASE-T over Cat5e/Cat6 for desktops and printers.
- Data Centers:
- Use 10GBASE-SR/LR fiber connections between switches and servers for high-speed transfer.
- Server Connections:
- Full-duplex and fiber connections are common for reliability and speed.
- Network Closets / Wiring Rooms:
- Patch panels with 802.3 Ethernet ports connect multiple floors or rooms.
7. Key Exam Tips
- Remember the “BASE-T” naming convention for copper, “BASE-SX/LX” for fiber.
- Know the max cable lengths for twisted-pair (100 m) vs. fiber (varies with type).
- Duplex type (half vs full) and collision handling are critical concepts.
- Fiber vs copper: Fiber = longer distance, higher speed, immune to electromagnetic interference; Copper = cheaper, easy to install.
- Speeds to focus on for the exam: 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps.
✅ Summary for Students
802.3 standards define how Ethernet works over wired media. They cover cable types, speeds, distances, and how data is framed and transmitted. In practical IT environments, knowing which 802.3 standard fits where is essential for designing and troubleshooting networks.
