Cisco Certified Network Associate (CCNA) 200-301 · Free study guide

Objective 1.3 — Compare interfaces and cabling

Media selection is an engineering decision about distance, bandwidth, power, interference, environment, and cost. A connector that physically fits is not proof that the optical wavelength, fiber type, speed, or transceiver is compatible.

Copper Ethernet

Twisted-pair copper is common for endpoint access. It is inexpensive, supports standard Ethernet distances for its category and speed, and can carry Power over Ethernet. Copper is affected by electromagnetic conditions and requires correct pair termination. The negotiated link speed is limited by both interfaces and the installed channel.

Shared Ethernet media historically placed multiple stations in one collision domain. Modern switched full-duplex Ethernet gives a point-to-point link between an endpoint and switchport, eliminating normal collisions on that segment.

Multimode and single-mode fiber

Multimode fiber carries multiple light paths through a wider core and is used for many building and data-center distances with compatible optics. Single-mode fiber uses a much smaller core and supports much longer distances with its matching optics. Neither is universally “faster”; the Ethernet standard, optic, fiber, distance, and power budget determine the supported link.

Fiber resists electromagnetic interference and provides electrical isolation, but connectors require cleanliness and bend limits. Mixing unsupported optic and fiber combinations may produce a dark or unreliable link.

Point-to-point connections

A point-to-point Ethernet link has one transmitter/receiver relationship at each end. Switch-to-host, router-to-router, and many switch uplinks operate this way. Each end must agree on supported speed and duplex behavior. A shared medium has multiple participants contending for access; Wi-Fi remains a practical shared- medium example even though its framing differs from wired Ethernet.

Selection method

State required bandwidth and distance first. Add environmental constraints, whether PoE is required, available interface types, redundancy, and installation cost. Confirm the full bill of materials: interface, transceiver, wavelength, fiber or copper category, connector, and patch path. Record maximum supported distance under the actual standard rather than applying one number to all media.

Worked scenario

An access point 40 meters from a closet needs data and power, so supported copper with PoE is a direct fit. A link between buildings needs electrical isolation and exceeds the chosen multimode optic's reach, so compatible single-mode fiber and optics are appropriate. Short data-center links may use multimode when its reach and economics fit. The answer changes if power, distance, or installed plant changes.

Common traps

• Selecting fiber type without checking the optic.
• Assuming all copper links support PoE or the required power level.
• Applying a distance limit from one Ethernet standard to another.
• Calling switched full-duplex Ethernet shared media.
• Cleaning configuration when physical loss or dirty fiber is the evidence.

Readiness checklist

• I can justify copper, multimode, or single-mode from requirements.
• I can distinguish shared media from point-to-point Ethernet.
• I check transceiver, wavelength, connector, and medium as one system.
• I know link light is only the first verification step.