Demystifying Ethernet Network Interface Cards: Structure and Working Principles
Demystifying Ethernet Network Interface Cards: Structure and Working Principles
· Jomplair · All Blogs Networking Technology

The Physical Anatomy of an Ethernet NIC

 

  1. The Connector: RJ45 Jack
The RJ45 port is your gateway to wired networks. Key features include:
  • Pin Configuration:
    • 100Mbps Ethernet: Uses 4 wires (Pairs 1-2 for TX, 3-6 for RX)
    • 1000Mbps Ethernet: Utilizes all 8 wires (Pairs 1-2 TX, 3-6 RX, 4-5/7-8 bidirectional)
  • LED Indicators:
    • Green: Link status (steady = connected)
    • Amber: Data activity (blinking = transmission)

 

  1. The Signal Transformer
This component serves three critical functions:
  1. Electrical Isolation: Prevents ground loops (up to 1500V protection)
  2. Impedance Matching: Maintains signal integrity (100Ω for Cat5e/6)
  3. EMI Reduction: Filters high-frequency noise
Pro Tip: Integrated transformers in RJ45 jacks (e.g., HR911105A) simplify PCB design but cost 20% more than discrete solutions.
 

 

The Core Components: PHY vs. MAC

 

  1. Physical Layer Transceiver (PHY)
The PHY chip converts digital data to analog signals using:
  • Modulation: PAM-3 for 100BASE-TX, PAM-5 for 1000BASE-T
  • Encoding: 4B/5B for Fast Ethernet, 8B/10B for Gigabit
Key Specs:
 
Parameter 100Mbps PHY 1000Mbps PHY
Power Consumption 0.5W 1.2W
Latency <100ns <50ns

 

  1. Media Access Controller (MAC)
The MAC layer handles:
  • Frame Assembly: Adds source/destination MAC addresses
  • CSMA/CD: Collision detection and retransmission
  • Flow Control: PAUSE frames for congestion management
Memory Buffering:
  • TX/RX FIFO: Typically 8-16KB per port
  • DMA Channels: 4-8 channels for priority queuing

 


 

Data Flow: From CPU to Cable

 

  1. Transmission Process
User Data → TCP/IP Stack → MAC (Frame Assembly) → PHY (Signal Conversion) → RJ45 → Network
Critical Stages:
  1. DMA Transfer: CPU offloads data to NIC memory
  2. CRC Generation: 32-bit error check (99.9999% accuracy)
  3. Auto-Negotiation: Determines speed/duplex (e.g., 1000BASE-T full duplex)
  4. Reception Process
Network → RJ45 → PHY (Signal Recovery) → MAC (Frame Check) → TCP/IP Stack → Application
Error Handling:
  • FCS Validation: Discards frames with CRC errors
  • Jumbo Frames: Supports up to 9KB packets (vs. standard 1.5KB)

 


 

Interface Technologies: MII, RGMII, and Beyond

 

  1. Common Interfaces
 
Interface Speed Data Width Clock Rate
MII 100Mbps 4-bit 25MHz
RMII 100Mbps 2-bit 50MHz
RGMII 1000Mbps 4-bit 125MHz

 

  1. Signal Timing Example (RGMII)
TX_CLK ───┐ ┌─── 1. Data valid on rising edge ├─────┤ TXD[3:0] ─┘ └─── 2. Data valid on falling edge
This DDR (Double Data Rate) technique halves the required clock frequency.
 

 

Advanced Features in Modern NICs

 

  1. Energy Efficient Ethernet (EEE)
Reduces power by 50-60% during idle periods through:
  • Low Power Idle (LPI): Sleep mode between packet bursts
  • Adaptive Rate Control: Dynamically adjusts link speed
  1. Virtualization Support
  • SR-IOV: Allows 16-64 virtual functions per physical port
  • RSS (Receive Side Scaling): Distributes traffic across CPU cores

 


 

Choosing the Right NIC: Decision Factors

 

  1. Performance Metrics
 
Requirement Recommended Spec
Video Production 10Gbps, TOE Enabled
Industrial IoT 1Gbps, <10μs Latency
Home Office 2.5Gbps, EEE Support

 

  1. Compatibility Checklist
  • Driver Support: NDIS 6.30+ for Windows, ioctl for Linux
  • Protocol Offload: TCP/UDP checksum, VLAN tagging
  • Temperature Range: -40°C to 85°C for industrial use

 


 

Troubleshooting Common Issues

 

  1. Link Failures
Diagnosis Flow:
  1. Check link lights
  2. Test with known-good cable
  3. Verify auto-negotiation settings
  4. Update PHY firmware
  5. Performance Degradation
Optimization Steps:
  • Enable jumbo frames (if supported end-to-end)
  • Adjust interrupt coalescence (100-200μs optimal)
  • Implement QoS prioritization

 


 
Future Trends:
  • Multi-Gig NICs: 2.5G/5G/10G becoming mainstream
  • PCIe 5.0 Interface: 32GT/s bandwidth for 100G NICs
  • Photonics Integration: Silicon photonics for lower power

Latest posts