You must cable an Ethernet network in an older building with limited workspace. The new cable must share conduit with existing telephone wiring, and some runs will be up to 135 m. Which medium is best suited to meet distance and interference constraints?

Introduction / Context:
Ethernet media choices depend on distance, bandwidth, and electromagnetic environment. Standard copper Ethernet channels are limited to ~100 m and are susceptible to EMI, particularly when sharing conduits with telephone or power cables. Fibre-optic cabling addresses both constraints by providing longer reach and immunity to electrical interference.

Given Data / Assumptions:

• Shared conduit with telephone cabling → increased EMI risk.
• Required run length up to 135 m → beyond common copper Ethernet limit.
• Desire for reliable performance without intermediate active devices.

Concept / Approach:
Fibre uses light instead of electrical signals, so it is immune to EMI and crosstalk from adjacent conductors. Multimode fibre with appropriate transceivers supports 1 Gbps and higher over hundreds of meters, easily covering 135 m. CAT1 is for voice only and unsuitable for Ethernet. CAT3 is limited and still constrained to ~100 m for older Ethernet variants. 10BASE5 thick coax is bulky, obsolete, and impractical for shared conduit in modern installs.

Step-by-Step Solution:

Verification / Alternative check:
Standards such as 1000BASE-SX/LX recommend fibre for building risers and campus links; many codes also prefer fibre in shared conduits due to its immunity and safety profile compared with high-frequency copper signaling near telecom circuits.

Why Other Options Are Wrong:

• CAT1: voice only; unsuitable for Ethernet.
• CAT3: legacy 10 Mbps support and still limited to ~100 m; EMI remains a concern.
• 10BASE5: obsolete, bulky, and not aligned with modern structured cabling.
• Flat silver satin: unshielded voice cord; not standards-compliant for Ethernet.

Common Pitfalls:
Attempting to exceed 100 m copper limits without active devices; underestimating EMI in shared conduits; ignoring transceiver selection and connector types (LC/SC) when planning fibre runs.

Final Answer:
Fibre-optic cable