Physical Connections

Part of Networking

The cables, wireless links, and other media that carry network signals.

Why This Matters

Every network ultimately depends on physical connections — some medium through which signals travel. Choosing the right physical medium for each part of a network determines its performance, reliability, cost, and ease of maintenance. The wrong choice creates bottlenecks, installation headaches, and reliability problems that persist for years because physical infrastructure is expensive to replace.

Physical connections are the most visible and tangible part of a network. They are also the most common source of problems — a pulled cable, a corroded connector, or water in a conduit causes more real-world network failures than all software issues combined. Understanding physical connections means understanding both how to build them right the first time and how to diagnose them when they fail.

Twisted Pair Copper Cable

Twisted pair cable is the standard medium for LAN connections. It consists of pairs of copper wires twisted around each other. The twisting provides a critical benefit: electromagnetic interference affects both wires in the pair equally, and the differential signaling used by Ethernet amplifies the difference between the wires while canceling the common-mode noise. This noise cancellation makes twisted pair resistant to the electrical interference that would corrupt signals on untwisted wires.

Category ratings determine the cable’s bandwidth capacity:

• Cat3: Supports 10 Mbps Ethernet. Telephone cable is typically Cat3.
• Cat5e: Supports 100 Mbps and 1 Gbps over 100 meters. The standard for most installations from the late 1990s onward.
• Cat6: Supports 1 Gbps with better noise margins, and 10 Gbps over up to 55 meters with careful installation.
• Cat6a: Supports 10 Gbps over 100 meters. Heavier and more expensive than Cat6, but the right choice for installations intended to last 15+ years.
• Cat7/Cat8: Higher category cables for data center use. Rarely needed for standard building installations.

Unshielded Twisted Pair (UTP) is standard for most installations. Shielded Twisted Pair (STP) or Screened Twisted Pair (ScTP) adds metallic shielding around the pairs to reduce radiated emissions and improve resistance to external interference. Shielded cable requires grounded connectors and continuous shield bonding to be effective — improperly grounded shielded cable can be worse than UTP. Use shielded cable only in environments with strong electromagnetic interference (industrial machinery, radio transmitters) and only if you can implement the grounding correctly.

Coaxial Cable

Coaxial cable consists of a center conductor surrounded by a tubular dielectric (insulator), which is surrounded by a tubular shield conductor, which is covered by an outer jacket. The geometry provides excellent shielding and controlled impedance.

50-ohm coaxial cable (RG-58 for thin Ethernet, RG-11 for thick Ethernet) was used in early Ethernet bus networks. 75-ohm coaxial cable (RG-6, RG-59) is used for cable television and is structurally similar but not interchangeable for Ethernet purposes.

Coaxial cable is stiffer and more expensive than twisted pair but provides better shielding and can span longer distances. It is used in environments where the shielding is essential (proximity to strong RF sources) and in long-distance applications where twisted pair’s 100-meter limit is insufficient.

For new networking installations, coaxial cable is rarely appropriate — twisted pair with a switch provides better performance at lower cost. Coaxial cable is more likely encountered when repurposing existing CATV (cable television) infrastructure for network use.

Fiber Optic Cable

Fiber optic cable transmits data as pulses of light rather than electrical signals. This provides several important advantages: immunity to electromagnetic interference (light is not affected by magnetic or electric fields), electrical isolation between the connected devices (no current path between the ends of the fiber), and the ability to span much greater distances without signal amplification.

Single-mode fiber (SMF) has a very small core (8-10 micrometers) and allows only a single propagation mode. It is used for long distances (up to hundreds of kilometers with amplification). Single-mode fiber requires laser light sources and more precise connectors, making it more expensive.

Multimode fiber (MMF) has a larger core (50 or 62.5 micrometers) and allows multiple propagation modes. It is used for shorter distances (up to a few kilometers) and can use less expensive LED light sources. Multimode fiber is the practical choice for building-level connections where electrical isolation or long distances are needed.

Fiber optic cables require careful handling. The fiber itself (glass or plastic) can break if bent too sharply — most fiber has a minimum bend radius of 25-50mm. The fiber end faces must be cleaved (cut cleanly) and polished to minimize insertion loss. Dirt on the end face causes significant signal loss and can damage mating connectors. Fiber connectors must be cleaned before every connection.

Fiber optic termination requires either factory-terminated cables (ordered to specific lengths) or field-termination tools (mechanical splices or fusion splicers). Fusion splicers weld two fiber ends together with minimum loss but cost thousands of dollars. Mechanical splices use a gel-filled connector that aligns two fiber ends — adequate for many applications at much lower cost.

Wireless Connections

Wireless networking uses radio waves rather than cables. 802.11 (Wi-Fi) is the standard for wireless LAN connections, operating in the 2.4 GHz and 5 GHz ISM (Industrial, Scientific, and Medical) bands.

Range is limited by signal strength, which decreases with distance (inverse square law) and is further reduced by walls, floors, and other obstacles. Metal, concrete, and water absorb radio waves significantly. Glass and wood have less effect. A typical Wi-Fi access point provides usable connectivity within 30-100 meters in open space, less in buildings.

Wireless is not a replacement for wired connections where reliability and performance matter. Wireless signals are subject to interference from neighboring networks on the same channel, microwave ovens, Bluetooth devices, and other radio sources. Throughput is shared among all devices associated with a given access point. For servers, fixed workstations, and any application requiring consistent performance, wired connections are strongly preferred.

Point-to-point wireless links using directional antennas can extend network connectivity across distances impossible for cable. A pair of directional 5 GHz antennas on line-of-sight towers can provide 100+ Mbps links across several kilometers. This is the practical way to connect buildings separated by more than 100 meters without burying cable.

Cable Installation Best Practices

Pull cable before installing connectors whenever possible. Pre-terminated cables (patch cables) are appropriate for short runs in equipment rooms. For in-wall runs, pull unfinished cable and terminate after installation.

Maintain the twist pairs as close to the termination point as possible. Untwisting pairs to make connections is unavoidable, but keep untwisted lengths to a minimum (25mm maximum for Cat5e, less for higher categories). Excessive untwisting is a common cause of crosstalk and reduced performance.

Avoid routing cable parallel to electrical wires for extended distances. Electrical cables radiate interference that can couple into network cables. Where parallel runs are unavoidable, maintain at least 100mm separation from 120V/240V wiring and more from high-current circuits.

Label every cable at both ends during installation. Labels applied during installation are easy and cost-free; labels applied during troubleshooting require taking the network down or working blind. A simple labeling scheme (building-floor-room-port-number) makes cable identification quick in any situation.