59  Wired Access: Ethernet

Key Concepts
  • Ethernet: The dominant wired LAN standard (IEEE 802.3); defines the physical layer and MAC protocol for wired networks
  • PoE (Power over Ethernet): Delivering DC power alongside data over the same Ethernet cable; eliminates separate power wiring for IoT devices (cameras, access points, sensors)
  • CSMA/CD: The original Ethernet MAC protocol; deprecated in modern full-duplex switched Ethernet where collisions are physically impossible
  • Industrial Ethernet: Deterministic extensions of standard Ethernet for industrial automation (PROFINET, EtherNet/IP, EtherCAT); provides microsecond-level timing
  • Cat5e/Cat6 Cable: Twisted-pair Ethernet cable categories; Cat5e supports Gigabit Ethernet up to 100 m, Cat6 provides better crosstalk performance
  • Auto-Negotiation: The process by which two Ethernet devices agree on the highest common speed and duplex mode without manual configuration
  • Switched Ethernet: Modern Ethernet topology where each device has a dedicated full-duplex link to a switch port, eliminating shared medium collisions

59.1 In 60 Seconds

Ethernet (IEEE 802.3) provides the most reliable IoT connectivity with deterministic latency, no interference, and speeds from 10 Mbps to 10 Gbps over twisted-pair copper or fiber. Power over Ethernet (PoE) delivers up to 100W (IEEE 802.3bt Type 4) through the same cable, eliminating separate power wiring for IP cameras, access points, and industrial sensors. Ethernet is ideal for stationary IoT devices where reliability matters more than mobility—think factory floors, security systems, and building automation gateways.

Learning Objectives

By the end of this section, you will be able to:

  • Explain the role of Ethernet (IEEE 802.3) in IoT deployments and justify when it is preferable to wireless alternatives
  • Compare and differentiate Ethernet standards (10BASE-T, 100BASE-T, 1000BASE-T) by speed, application, and physical layer characteristics
  • Select appropriate Ethernet standards for given IoT use cases based on bandwidth and latency requirements
  • Evaluate trade-offs between wired Ethernet and wireless connectivity for specific IoT deployment scenarios
  • Calculate PoE power budgets for IoT installations using IEEE 802.3af, 802.3at, and 802.3bt standards

59.2 Prerequisites

Before diving into this chapter, you should be familiar with:

Ethernet is the most common wired networking technology. Think of Ethernet cables as highways for data - they’re fast, reliable, and can carry lots of traffic without interruption.

When you plug your computer into a router with a cable, that’s Ethernet! The cable has 8 wires inside arranged in twisted pairs that carry electrical signals representing your data.

Term Simple Explanation
Ethernet Wired connection using twisted-pair cables (like RJ45 “phone jack” connectors)
100BASE-T Fast Ethernet - 100 Mbps (megabits per second)
1000BASE-T Gigabit Ethernet - 1000 Mbps (10x faster than 100BASE-T)
PoE Power over Ethernet - delivers both data AND electricity through one cable
Cat5e/Cat6 Cable quality ratings - higher numbers = better performance

“Why would anyone use wires when wireless is so convenient?” asked Sammy the Sensor. Max the Microcontroller had a quick answer. “Reliability! Ethernet never drops out because of interference, it delivers data at consistent speed, and it can even provide power through the same cable.”

“Power over Ethernet is amazing,” said Lila the LED. “A single Ethernet cable plugs into a security camera and delivers both the network connection AND up to 90 watts of power. No separate power cable needed! That is why PoE is so popular for IP cameras, Wi-Fi access points, and building sensors.”

“Ethernet also has zero radio interference,” added Bella the Battery. “In a factory with lots of motors, welders, and heavy machinery that mess up wireless signals, a wired Ethernet connection keeps working perfectly. For critical infrastructure like factory control systems and building automation gateways, wired is the way to go.”

“The trade-off is obvious though,” said Sammy. “You cannot put Ethernet cables in a farmer’s field or on a moving robot. Ethernet is perfect for STATIONARY devices where reliability matters more than mobility. Match the connection type to the job!”

59.3 IEEE 802.3 Ethernet for IoT

Time: ~8 min | Difficulty: Intermediate | Reference: P07.C11.U02

IoT devices may be connected via a wired connection. For permanent installations, Ethernet is commonly used. The data rate using Ethernet can range from 10 Mbps to more than 1 Gbps (1000 Mbps).

Timeline diagram showing Ethernet standard evolution from 10BASE-T (10 Mbps) through 100BASE-T (Fast Ethernet), 1000BASE-T (Gigabit), 10GBASE-T (10 Gbps), and Power over Ethernet variants (PoE, PoE+, PoE++), with IEEE 802.3 amendment designations and power delivery capabilities for each generation
Figure 59.1: Evolution of Ethernet standards showing increased speeds and Power over Ethernet capabilities

59.3.1 Common Ethernet Standards

10BASE-T: 10 Mbps, found on small microcontrollers and legacy industrial equipment

100BASE-T: 100 Mbps (Fast Ethernet), common on higher-powered microcontrollers or single-board computers like Raspberry Pi

1000BASE-T: 1000 Mbps (Gigabit Ethernet), used for high-bandwidth applications like IP cameras and industrial gateways

59.4 Quick Check: Ethernet Standards

Examples of Ethernet-Connected IoT Devices
  • IP Cameras: 4K video transmission. Transmitting 4K quality video over Wi-Fi may create problems due to data speed constraints
  • VoIP Devices: Voice over IP communications requiring consistent quality
  • Set-top Boxes: Video/audio streaming and storage
  • Game Applications and Systems: Low-latency gaming
  • Static Industrial Equipment: Manufacturing machinery, process control
  • High-Security Sensors: Transmitting via wireless is viewed as high-risk; wired preferred
  • High-Reliability Control: Robotics, medical applications requiring deterministic communication

59.4.1 Advantages of Ethernet for IoT

Advantage Description
High bandwidth 10 Mbps to 10+ Gbps - supports any IoT data rate
High reliability No radio interference, consistent performance
Low latency Sub-millisecond latency for real-time control
Deterministic Predictable timing (critical for industrial)
PoE capability Single cable for data AND power
Security Physical access required - no wireless eavesdropping

Ethernet’s maximum cable length is set by signal attenuation physics. Cat6 cable attenuation at 100 MHz is approximately 20 dB per 100 meters (per TIA-568-C standard).

For Gigabit Ethernet (1000BASE-T), the 100 m limit is derived from the signal-to-noise ratio needed for reliable PAM-5 decoding across four wire pairs. The IEEE 802.3 standard specifies an end-to-end channel loss budget:

\[\text{Max channel insertion loss} \approx 21 \text{ dB at } 100 \text{ MHz (Cat5e)}\]

\[\text{Cat6 attenuation at 100 MHz} \approx 19.8 \text{ dB/100m}\]

At 100 m, the received signal is close to the noise floor, leaving minimal margin. Beyond 100 m, bit error rates rise sharply and automatic repeat request (ARQ) overhead degrades throughput. A repeater or switch must be placed every 100 m to regenerate the signal.

For 10 Gbps (10GBASE-T), the more demanding modulation scheme (PAM-16) requires better SNR, which is why it is limited to 55 m on Cat6 cable and requires Cat6A (10GBASE-T is specified for 100 m only on Cat6A or Cat7).

59.4.2 Disadvantages of Ethernet for IoT

Disadvantage Description
Physical cabling Requires cable runs to each device
Installation cost Labor-intensive, especially retrofit
Limited mobility Devices must be stationary
Not battery-powered Requires mains or PoE infrastructure
Inflexible Difficult to relocate devices
MVU: Power over Ethernet (PoE)

Core Concept: PoE delivers DC power (15-90W) alongside data over standard Ethernet cables, eliminating separate power wiring for IoT devices like IP cameras, access points, and sensors.

Why It Matters: A single cable installation reduces deployment cost by 30-50% for devices that would otherwise need both Ethernet and power outlets. PoE switches also enable centralized power management and UPS backup for all connected devices.

Key Takeaway: Use PoE (802.3af, 15.4W) or PoE+ (802.3at, 30W) for cameras, access points, sensors, and thin clients. PoE++ (802.3bt Type 3: 60W, Type 4: 100W) supports higher-power devices like PTZ cameras and small displays. Always verify both the switch and the device support the same PoE standard before deployment.

Worked Example: Ethernet vs Wi-Fi for 4K Video Surveillance

Scenario: A warehouse needs 50 IP cameras for security. Each camera streams 4K video at 25 Mbps. The warehouse is 200m x 150m with metal shelving causing RF interference.

Given:

  • 50 cameras, each producing 25 Mbps video stream
  • Total bandwidth: 50 x 25 Mbps = 1,250 Mbps (1.25 Gbps)
  • Distance from cameras to switches: 50-80 meters
  • Environment: Metal shelving, forklifts, variable lighting

Analysis:

Option A: Wi-Fi 5 (802.11ac)

  • Theoretical: 3.5 Gbps shared (8x8 MU-MIMO, 160 MHz)
  • Practical: 1-2 Gbps shared across all devices
  • 50 cameras competing for airtime
  • Metal interference causes unpredictable dropouts
  • Result: Insufficient - video stuttering, dropped frames

Option B: Gigabit Ethernet with PoE+

  • Each camera gets dedicated 1 Gbps port
  • 25 Mbps uses only 2.5% of available bandwidth
  • No radio interference
  • PoE+ provides up to 30W power per camera
  • Result: Optimal - consistent 4K streaming

Cost Comparison (50 cameras):

Item Wi-Fi Ethernet
Infrastructure $3,000 (6 APs) $8,000 (2x 24-port PoE switches)
Cabling $500 (power drops) $5,000 (Cat6 runs)
Power outlets $2,500 (50 outlets) $0 (PoE)
Total $6,000 $13,000
Reliability Variable Excellent

Result: Ethernet costs more upfront but provides guaranteed performance. For mission-critical surveillance, the additional $7,000 is justified by eliminating video loss during incidents.

Key Insight: The text states cameras are Ethernet examples because “Transmitting 4K quality video over Wi-Fi may create problems due to data speed constraints.” Ethernet’s deterministic performance is essential for security applications.

Worked Example: Selecting Protocol for Industrial Robots

Scenario: A factory needs to connect 50 industrial robots across a 200m x 150m floor. Robots require telemetry every 100ms with <10ms latency and zero packet loss for safety.

Given:

  • 50 robots with 100ms update interval
  • Latency requirement: <10ms
  • Packet loss: Zero tolerance (safety-critical)
  • Data per update: 500 bytes
  • Total bandwidth: 50 x (500 bytes x 8 / 0.1s) = 2 Mbps

Requirements Analysis:

Requirement Wi-Fi 6 LoRaWAN Zigbee Ethernet+TSN
Latency 3-200ms 2500ms 60ms 0.069ms
Packet Loss 1-5% 5-10% 5-10% 0%
Deterministic No No No Yes
Bandwidth 9.6 Gbps 50 kbps 250 kbps 1 Gbps

Analysis:

The text explicitly lists “Robotics, medical applications requiring deterministic communication” as Ethernet examples, citing advantages of “Low latency and jitter” and “Deterministic performance.”

  • Wi-Fi: 3.7ms typical but 50-200ms worst-case spikes (non-deterministic). 1-5% packet loss unacceptable for robot safety.
  • LoRaWAN: 2,500ms latency is 250x too slow. Transmission time (1.45s) exceeds update interval (100ms).
  • Zigbee: 60ms latency > 10ms requirement. 250 kbps cannot support 50 robots reliably.
  • Ethernet + TSN: 0.069ms latency with zero jitter. Time-Sensitive Networking guarantees bounded latency.

Result: Gigabit Ethernet with TSN (Time-Sensitive Networking) is the only viable option. TSN extensions (IEEE 802.1Qbv) provide deterministic scheduling, ensuring robot control packets are never delayed.

Key Insight: For safety-critical industrial control, only wired Ethernet can guarantee the bounded latency and zero packet loss required. Wireless protocols are fundamentally non-deterministic due to shared medium access.

59.5 Knowledge Check

59.6 Working Code: PoE Budget Calculator

Planning a PoE deployment requires matching your switch’s power budget to the devices you need to power. This Python tool calculates whether your PoE switch can handle the load and identifies potential oversubscription.

"""PoE (Power over Ethernet) Budget Calculator for IoT Deployments."""

# IEEE PoE standards
POE_STANDARDS = {
    "802.3af":  {"max_per_port_W": 15.4, "class_name": "PoE (Type 1)"},
    "802.3at":  {"max_per_port_W": 30.0, "class_name": "PoE+ (Type 2)"},
    "802.3bt3": {"max_per_port_W": 60.0, "class_name": "PoE++ (Type 3)"},
    "802.3bt4": {"max_per_port_W": 90.0, "class_name": "PoE++ (Type 4)"},
}

def poe_budget_check(switch_budget_W, devices):
    """Check if PoE switch can power all connected IoT devices.

    Args:
        switch_budget_W: Total PoE power budget of the switch (watts)
        devices: List of dicts with 'name', 'count', 'watts', 'poe_class'
    """
    print(f"PoE Power Budget Analysis")
    print(f"Switch budget: {switch_budget_W}W")
    print("=" * 60)

    total_max_W = 0
    total_typical_W = 0
    total_devices = 0

    print(f"\n  {'Device':<25s} {'Count':>5s} {'Each':>6s} {'Total':>7s} {'Standard'}")
    print(f"  {'-'*55}")

    for dev in devices:
        max_w = dev["watts"] * dev["count"]
        # Typical draw is ~70% of max for most PoE devices
        typical_w = max_w * 0.7
        std = POE_STANDARDS.get(dev["poe_class"], {})
        std_name = std.get("class_name", "Unknown")
        max_port = std.get("max_per_port_W", 0)

        # Check if device exceeds its PoE class
        over = " OVER!" if dev["watts"] > max_port else ""
        print(f"  {dev['name']:<25s} {dev['count']:>5d} {dev['watts']:>5.1f}W "
              f"{max_w:>6.1f}W  {std_name}{over}")

        total_max_W += max_w
        total_typical_W += typical_w
        total_devices += dev["count"]

    print(f"\n  {'TOTALS':<25s} {total_devices:>5d} {'':>6s} {total_max_W:>6.1f}W max")
    print(f"  {'':25s} {'':>5s} {'':>6s} {total_typical_W:>6.1f}W typical (70%)")

    # Budget analysis
    headroom_max = switch_budget_W - total_max_W
    headroom_typ = switch_budget_W - total_typical_W
    utilization = total_max_W / switch_budget_W * 100

    print(f"\n  Budget Analysis:")
    print(f"  {'─'*40}")
    print(f"  Max power draw:     {total_max_W:>6.1f}W / {switch_budget_W}W "
          f"({utilization:.0f}%)")
    print(f"  Headroom (max):     {headroom_max:>+6.1f}W")
    print(f"  Headroom (typical): {headroom_typ:>+6.1f}W")

    if headroom_max < 0:
        deficit = abs(headroom_max)
        print(f"\n  WARNING: Budget exceeded by {deficit:.0f}W!")
        print(f"  Switch will shed lowest-priority ports.")
        print(f"  Fix: Upgrade to {total_max_W * 1.2:.0f}W+ switch")
    elif utilization > 80:
        print(f"\n  CAUTION: >80% utilization. No room for expansion.")
    else:
        spare_devices_15W = int(headroom_max / 15)
        print(f"\n  OK: Can add ~{spare_devices_15W} more 15W devices")

    return {"total_max_W": total_max_W, "utilization_pct": utilization}


# Example: Office building IoT deployment
poe_budget_check(switch_budget_W=370, devices=[
    {"name": "IP Camera (1080p)",      "count": 12, "watts": 12.5, "poe_class": "802.3af"},
    {"name": "IP Camera (4K PTZ)",     "count": 4,  "watts": 25.0, "poe_class": "802.3at"},
    {"name": "Wi-Fi 6 Access Point",   "count": 6,  "watts": 18.0, "poe_class": "802.3at"},
    {"name": "VoIP Phone",             "count": 20, "watts": 6.5,  "poe_class": "802.3af"},
    {"name": "IoT Sensor Gateway",     "count": 3,  "watts": 8.0,  "poe_class": "802.3af"},
    {"name": "Door Access Controller", "count": 4,  "watts": 10.0, "poe_class": "802.3af"},
])

Why this matters: A 48-port PoE switch might advertise 370W total budget but support 30W per port. If you connect 24 devices at 15W each (360W), the switch is near capacity and cannot support a 25th device at full power. Always calculate the aggregate budget, not just per-port limits.

Try It: PoE Switch Budget Calculator

Adjust the device counts to see whether your PoE switch budget is sufficient. The calculator shows peak and typical draw and flags oversubscription.

Common Pitfalls

Standard Ethernet (100BASE-TX, 1000BASE-T) is limited to 100 m per segment. Exceeding this causes signal degradation and high bit error rates. Fix: use a switch or Ethernet extender for runs over 100 m, or switch to fibre optic.

A 24-port PoE switch may have a total power budget of 370 W. Connecting 24 devices each drawing 15.4 W (PoE) exceeds the budget by 2×. Fix: calculate total PoE load and verify it does not exceed the switch’s power budget before deployment.

Poorly terminated connectors, damaged cable jackets, or incompatible cable categories cause Ethernet errors that are harder to diagnose than RF issues. Fix: test Ethernet links with a cable tester before deployment and verify auto-negotiation is operating correctly.

59.7 Summary

Ethernet remains the gold standard for wired IoT connectivity, offering unmatched reliability and performance for stationary devices.

Key Takeaways

When to Use Ethernet:

  • High-bandwidth applications (video, large data transfers)
  • Mission-critical systems requiring deterministic timing
  • Security-sensitive deployments (no wireless eavesdropping)
  • Static installations where cabling is feasible
  • Devices that can benefit from PoE (cameras, access points, sensors)

Ethernet Standards for IoT: | Standard | Speed | Use Case | |———-|——-|———-| | 10BASE-T | 10 Mbps | Legacy equipment, simple sensors | | 100BASE-T | 100 Mbps | Microcontrollers, basic IoT | | 1000BASE-T | 1 Gbps | Cameras, gateways, industrial | | PoE (802.3af) | 15.4W | Basic cameras, VoIP phones, sensors | | PoE+ (802.3at) | 30W | 4K cameras, Wi-Fi 6 APs, access control | | PoE++ (802.3bt) | 60W/100W | PTZ cameras, displays, thin clients |

Best Practices:

  1. Use PoE whenever possible to simplify installation
  2. Plan cable runs during construction (cheaper than retrofit)
  3. Use Cat6 or better for future-proofing
  4. Consider TSN for industrial control applications
  5. Ethernet for backbone, wireless for edge where needed

59.8 What’s Next?

Topic Chapter Description
Wireless Wi-Fi for IoT Wireless Network Access: Wi-Fi for IoT IEEE 802.11 protocols including Wi-Fi 6 and Wi-Fi HaLow designed for IoT density and range requirements
Network Access Overview Network Access and Physical Layer Overview How the physical and network access layers fit into the OSI model and IoT protocol stacks
Bluetooth and BLE Bluetooth Low Energy for IoT Short-range wireless for wearables, beacons, and battery-powered sensors
LoRaWAN LoRaWAN for Wide-Area IoT Long-range, low-power WAN technology for outdoor and agricultural IoT sensors
Network Topologies IoT Network Topologies Star, mesh, bus, and hybrid topologies and when each suits specific IoT deployments
Industrial Protocols Industrial IoT Networking PROFINET, EtherNet/IP, and Time-Sensitive Networking (TSN) for deterministic industrial control