Core Networking · Study deck

Ethernet: Links and Standard Selection

This first route covers link identity, standard selection, device fit, and the evidence behind a wired choice.

Packet Pete is your guide for this deck.

networkphysicalwired

After studying this chapter

Learning objectives

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

Major section

Overview · Start With a Link You Can Inspect

This first route covers link identity, standard selection, device fit, and the evidence behind a wired choice.

The physical layer is the part of a network that carries signals through cable, fibre, or radio.
A protocol is an agreed set of rules for an exchange.
One green light cannot choose among them.

A terminated Ethernet patch lead shows a red jacket, molded strain relief and clear RJ45 plug with eight visible contacts. The photo does not expose the twist pattern inside the cable.

Major section

Key Concepts

Ethernet: The dominant wired LAN standard (IEEE 802.3); defines the physical layer and MAC protocol for wired networks.

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.

Major section

For Beginners: What is Ethernet? · Reliable Wired Connections

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.
The cable has 8 wires inside arranged in twisted pairs that carry electrical signals representing your data.
The microcontroller had a quick answer. "Reliability!

Major section

Powerline Networking as a Retrofit Link · IEEE 802.3 Ethernet for IoT

The acceptance test should then repeat while high-load appliances operate and after each adapter has restarted.

Powerline networking carries data over the building's existing mains wiring.
The convenience does not make the wiring a clean network medium.
IoT devices may be connected via a wired connection.

Evolution of Ethernet standards showing increased speeds and Power over Ethernet capabilities

Major section

Putting Numbers to It · MVU: Power over Ethernet (PoE)

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).
$\text{Category 6 channel insertion-loss limit} \approx 21.3 \text{ dB at } 100 \text{ MHz}$ .
Ethernet cabling is not only a connector choice.

Real photograph of ethernet cable (cat5e/cat6, rj45 connector)

Major section

Ethernet vs Wi-Fi for 4K Video · Checkpoint: Wired Fit

No radio contention on the camera-to-switch cable; shared uplinks still need capacity.

Illustrative scenario: A warehouse needs 50 IP cameras for security.
The warehouse is 200m x 150m with metal shelving that can reflect or obstruct radio signals.
Metal shelving can cause reflection or shadowing.

Major section

Select Protocols for Robots

Illustrative scenario: A factory needs to connect 50 industrial robots across a 200m x 150m floor.

Safety functions require a separate fail-safe design; no network can promise zero packet loss.
Wi-Fi: The illustrative 3-200 ms latency span fails this deadline at its upper end.
A real deployment needs its own worst-case and loss measurements.

Major section

Select Protocols for Robots (continued)

LoRaWAN: The illustrative 2,500 ms latency is 250 times the 10 ms deadline.

A 1.45 s transmission, if that is the chosen profile's measured airtime, also exceeds the 100 ms update interval.
Zigbee: The 60 ms latency exceeds this 10 ms deadline.
The robots need 2 Mb/s versus a 250 kb/s PHY rate — 8× too little, before overhead.
Key Insight: A nominal link speed cannot guarantee a safety deadline or zero loss.

Deck summary

Key takeaways

This first route covers link identity, standard selection, device fit, and the evidence behind a wired choice.

Ethernet: The dominant wired LAN standard (IEEE 802.3); defines the physical layer and MAC protocol for wired networks.
Ethernet is the most common wired networking technology.
The acceptance test should then repeat while high-load appliances operate and after each adapter has restarted.
Ethernet's maximum cable length is set by signal attenuation physics.

Retrieval practice

Recall check 1 of 5

Packet Pete says: answer from memory, then check your reasoning.

Q1A stationary camera has a feasible cable run and suffers heavy radio interference; which link is the stronger starting choice?

AChoose Wi-Fi because avoiding the cable makes deployment simpler and the site can use its existing wireless network.

BChoose the faster radio because its headline throughput provides enough margin for the installed camera traffic.

CChoose Bluetooth because smaller modules can carry the camera stream through a compact local link.

DChoose wired Ethernet, then check cable run and shared uplink capacity.

Show answer

Answer: D A fixed device can avoid radio contention with a serviceable wired link.

Retrieval practice

Recall check 2 of 5

Packet Pete says: answer from memory, then check your reasoning.

Q2A fixed sensor needs 25 Mb/s and a low-latency wired link; which lowest listed Ethernet class should be shortlisted and then measured for latency?

AShortlist 10BASE-T at 10 Mb/s because the sensor's 25 Mb/s load can be accommodated by the switched link.

BShortlist 100BASE-TX at 100 Mb/s, then measure installed latency.

CShortlist the 1 Mb/s serial link because the wired sensor stream will fit within its nominal rate.

DReject every wired link as unable to carry a 25 Mb/s stream.

Show answer

Answer: B 10BASE-T lacks the nominal rate, and speed alone does not prove latency.

Retrieval practice

Recall check 3 of 5

Packet Pete says: answer from memory, then check your reasoning.

Q3A factory needs to connect a legacy programmable logic controller (PLC) manufactured in 2005. The PLC supports Ethernet but the datasheet lists only 'IEEE 802.3 10BASE-T' support. Which Ethernet speed will this device operate at?

A100 Mbps, as if the PLC supported a 100BASE-TX Ethernet interface.

B1000 Mbps, as if the PLC supported a Gigabit Ethernet interface.

CUse the switch port speed because its negotiated rate determines throughput across the PLC link.

D10 Mbps, as specified by the PLC's 10BASE-T Ethernet interface.

Show answer

Answer: D The number prefix in Ethernet standard names indicates the speed in Mbps: 10BASE-T = 10 Mbps, 100BASE-TX = 100 Mbps, 1000BASE-T = 1000 Mbps (1 Gbps).

Retrieval practice

Recall check 4 of 5

Packet Pete says: answer from memory, then check your reasoning.

Q4Three cameras need 20 W each at their PoE switch ports; with a 20% total reserve, which minimum port class and switch budget fit?

A60 W total, with ports that may not each supply the required 20 W.

B802.3at-capable ports and at least 72 W total including 20% reserve.

C90 W per camera, treating the reserve as a per-port power demand.

D20 W total, counting only one camera and leaving no switch reserve.

Show answer

Answer: B 802.3at supplies up to 30 W per port; 3×20 W×1.2 = 72 W at the switch.

Retrieval practice

Recall check 5 of 5

Packet Pete says: answer from memory, then check your reasoning.

Q5A building needs continuous 25 Mbps video from each of 100 fixed security cameras. Serviceable cable runs and PoE switch ports are available at every camera, while the surveyed Wi-Fi cells are already congested. Which is the strongest starting access design?

AGigabit Ethernet with PoE to each serviceable fixed camera.

BCongested 5 GHz Wi-Fi cells for continuous fixed-camera video.

CA half Wi-Fi, half wired split without a capacity reason.

DEither access method without considering surveyed congestion.

Show answer

Answer: A At the stated 25 Mbps per camera, 100 cameras need 100 × 25 = 2,500 Mbps before overhead.

Print reference

Answers 1 of 2

Answer key.

D · A fixed device can avoid radio contention with a serviceable wired link.
B · 10BASE-T lacks the nominal rate, and speed alone does not prove latency.
D · The number prefix in Ethernet standard names indicates the speed in Mbps: 10BASE-T = 10 Mbps, 100BASE-TX = 100 Mbps, 1000BASE-T = 1000 Mbps (1 Gbps).
B · 802.3at supplies up to 30 W per port; 3×20 W×1.2 = 72 W at the switch.

Print reference

Answers 2 of 2

Answer key.

A · At the stated 25 Mbps per camera, 100 cameras need 100 × 25 = 2,500 Mbps before overhead.