In an era dominated by optical fiber, copper cables are often regarded as an “outdated” technology. However, the reality tells a different story. Around 70% of internal connections in global data centers still rely on copper cabling, twisted-pair cables remain the mainstream choice for enterprise local area networks, and copper cables have even found renewed applications in 5G fronthaul networks. This article explores the technological evolution, unique advantages and transformation pathway of copper communication cables in the modern digital era.

1. Twisted-Pair Cables: The Longest-Serving Communication Cable

Working Principle

Twisted-pair cables transmit differential signals through two insulated conductors twisted at a specific pitch. The twisting structure helps cancel electromagnetic interference (EMI), with tighter twists providing stronger anti-interference capability.

Evolution of Ethernet Cable Categories

Cat8: The “Final Chapter” or “Rebirth” of Copper Cables?

Cat8 (Class I and Class II) currently represents the highest-grade twisted-pair cable standard.

·         Class I (Shielded): 2000MHz, supports 25GBASE-T within 30 meters

·         Class II (Unshielded): 1200MHz, supports 40GBASE-T within 30 meters

Key technical breakthroughs of Cat8 include:

·         Independent shielding for each pair (S/FTP structure)

·         22–24 AWG conductors to reduce insertion loss

·         Strict control of alien crosstalk between pairs

Physical Limits of Twisted-Pair Copper Cables

The key bottlenecks for copper cables include:

·         Skin Effect: High-frequency signals concentrate on the conductor surface, reducing effective cross-sectional area.

·         Dielectric Loss: Energy losses in insulation materials at high frequencies.

·         Crosstalk (NEXT/FEXT/Alien): Electromagnetic coupling between wire pairs.

·         Return Loss: Signal reflections caused by impedance discontinuities.

The industry generally believes that 100Gbps transmission within 30 meters is close to the physical limit for twisted-pair copper cables. Cat8.2 (IEEE 802.3bq) is currently under development with a target of 50Gbps per pair.

2. Coaxial Cables: The Underrated Veteran

Structure and Impedance

Coaxial cables consist of an inner conductor (copper or copper-clad steel), dielectric insulation (foamed PE), outer conductor (copper braid or aluminum foil) and an outer jacket. Common impedance standards include 50Ω for communications/RF applications and 75Ω for video/CATV.

Modern Application Scenarios

DOCSIS 4.0 and the Revival of Coaxial Cables

DOCSIS 4.0 (Full Duplex DOCSIS) enables coaxial cables to achieve:

·         Downlink speeds up to 10Gbps

·         Uplink speeds up to 6Gbps

·         Significantly improved spectrum efficiency

This positions coaxial cables as an important “last 100 meters” solution in areas where FTTH deployment remains challenging.

3. Why Copper Cables Remain Irreplaceable in Data Centers

Why Data Centers Prefer Copper Cables

Three Main Copper Interconnect Forms in Data Centers

·         DAC (Direct Attach Copper): Passive copper cable with SFP+/QSFP+ connectors. Lowest cost and latency, ideal for connections within 7 meters.

·         AOC (Active Optical Cable): Active optical cable with integrated transceivers, combining copper cable convenience with optical transmission distance advantages.

·         Copper Cable + Optical Module Combination: Traditional architecture with the highest flexibility.

Typical Usage Ratios in Data Center Topologies

·         Inside racks (ToR switch to server): over 90% DAC

·         Between racks (EoR/MoR): AOC or optical fiber

·         Between buildings: optical fiber

4. Copper Cables Find a New Role in 5G Networks

5G fronthaul networks connecting BBU and AAU require:

·         25Gbps bandwidth (eCPRI)

·         Typical distances below 100 meters

·         Latency below 100μs

·         Strict power consumption control

Challenges of Traditional Solutions

·         Optical fiber + modules: High cost, high power consumption and complex deployment

·         Pure copper solutions: Limited bandwidth and transmission distance

The Solution: Copper Cables + DSP Technology

By integrating DSP chips at both cable ends and using PAM4 modulation with Forward Error Correction (FEC), a single Cat8/Cat6A pair can achieve:

·         25Gbps transmission within 30 meters

·         More than 40% lower power consumption

·         Over 30% lower costs

This has given copper cables a “second life” in 5G fronthaul deployment.

5. The Green Advantages of Copper Cables

Under global carbon reduction initiatives, copper cables are gaining attention for their environmental benefits.

6. Future Outlook for Copper Cables

Single Pair Ethernet (SPE)

Single-pair twisted cables enabling 1Gbps/10Gbps transmission for industrial IoT and automotive Ethernet applications such as 100BASE-T1 and 1000BASE-T1.

PAM4 Copper Cables

Using four-level pulse amplitude modulation to achieve 50Gbps transmission over existing Cat6A/Cat8 infrastructure.

Copper Interconnects in Co-Packaged Optics (CPO)

Chip-level copper interconnects may replace optical interconnects in certain CPO applications to reduce packaging costs.

Sustainable Copper Cables

Future copper cable manufacturing is expected to increasingly adopt recycled copper and bio-based insulation materials to reduce lifecycle carbon footprints.

Conclusion

Copper cables are far from becoming obsolete. Instead, the industry continues to reinvent itself to meet the demands of modern communication infrastructure. From home networking and data centers to 5G fronthaul and industrial IoT, copper cables offer unique advantages in cost, power efficiency and ultra-low latency, complementing optical fiber rather than competing directly with it. Future communication networks will likely adopt hybrid architectures in which fiber optics and copper cables work together, each serving the applications where they perform best.

Source：  EEPW