Local Network Design — Part 1: Physical Infrastructure and WLAN

Reference guide for the Networks & Systems written exam — part one. Covers physical infrastructure: structured cabling, transmission media and WLAN design.

1. Structured Cabling

Structured cabling is the set of passive components that make it possible to build a flexible, protocol-independent Local Area Network (LAN). In Europe the reference standard is EN 50173; internationally it is ISO/IEC 11801.

System Hierarchy

A cabling system is divided into three main subsystems:

• Campus Backbone: Connects different buildings to each other, almost exclusively via optical fibre.
• Building Backbone: Links the main technical room (MC — Main Cross-connect) to the floor distribution rooms (HC — Horizontal Cross-connect) via optical fibre or high-capacity copper backbones.
• Horizontal Cabling: Runs from the floor distribution room to the individual wall outlets (TO — Telecommunications Outlet). Uses copper cable with a maximum run length of 90 metres, plus 10 metres for patch cords.

Equipment and Rack Placement

The physical location of equipment follows the hierarchical model to optimise management and security:

• Router and Firewall: Located in the Main Cross-connect (MC), the central star point that handles WAN (ISP) ingress. Usually one router suffices; in critical environments two are used in a redundant pair (HA).
• Switches:
  • Core/Distribution: In the MC or IC (Intermediate Cross-connect) for high-speed backbone traffic switching.
  • Access: In floor cabinets (HC) to provide connectivity to user outlets.
• Patch Panels: Mounted in 19-inch rack cabinets to terminate fixed cables. Active connections to switches are made via patch cords.
• Rack Cabinets: Must be housed in locked technical rooms equipped with a UPS for power continuity and adequate ventilation.
• User Stations (UT): PCs and phones connect to wall outlets (TO) in the work area.

Wiring Standards

RJ45 termination schemes follow the TIA/EIA 568A and 568B standards. Today, thanks to the Auto MDI-X feature on switches, the distinction between straight-through and crossover cables is handled automatically by the hardware.

2. Components and Transmission Media

The physical limit for copper is 100 metres total per run.

Ethernet Cable Categories

Optical Fibre

Optical fibres are essential for backbones and wherever electromagnetic immunity is required.

• Multimode (OM3, OM4): Primarily used in Building Backbones (distances < 500 m). More economical; use LED/VCSEL light sources.
• Single-mode (OS1, OS2): Used in Campus Backbones (distances > 500 m, up to km). Use Laser sources and offer very high bandwidth.

Shielding and Nomenclature

The shielding nomenclature follows the X/YTP format (e.g. U/UTP, F/UTP, S/FTP), where the first letter indicates overall shielding and the second indicates per-pair shielding. In public buildings, LSZH (Low Smoke Zero Halogen) jacketing is mandatory to prevent toxic gas emission in case of fire.

For Ethernet transmission standards (IEEE 802.3), designations such as 10GBASE-T follow a precise structure:

• Speed (10G): Nominal throughput. Examples: 100 (Mbps), 1000 (1 Gbps), 10G (10 Gbps).
• Modulation (BASE): Stands for Baseband. The signal uses the entire available bandwidth of the medium, unlike Broadband.
• Physical Medium (-T): The suffix identifies the cable type or optical technology:
  • -T: Twisted Pair (Copper).
  • -SR / -SX: Short Range (Multimode Fibre).
  • -LR / -LX: Long Range (Single-mode Fibre).

Power over Ethernet (PoE)

Power over Ethernet (PoE) is a technology that delivers electrical power to remote devices over the same Ethernet cable used for data.

Advantages: Eliminates the need for local power adapters and electrical outlets near devices. Allows centralising power supply in the technical room (under UPS), ensuring operational continuity even during a blackout.

Requires compatible switches (PSE — Power Sourcing Equipment) and a total Power Budget calculation. Cat 6A is recommended for PoE++.

Exam tip: For a new installation, a solid justification is: “For horizontal cabling, Cat 6A F/UTP cables with LSZH jacket are chosen, ensuring 10GBASE-T support and high-power PoE+, in full compliance with fire safety regulations.”

3. Wireless Network Design (WLAN)

Architecture and Management

• Wireless Controller (WLC): A physical or virtual device that centralises network management. It automatically configures Access Points (APs), manages security, firmware updates and coordinates Roaming (users moving between cells without dropping the connection).
• Mesh Networks: APs connect to each other via radio (wireless backhaul) instead of cables.
  • When to use them: In historic buildings or outdoor areas where laying cables is impossible.
  • Drawbacks: Each wireless hop halves the available bandwidth and increases latency. For high-performance enterprise networks, wiring every AP physically is always preferable.

Configuration and Radio Frequencies

• Multi-SSID and VLANs: A single physical AP can broadcast multiple logical networks (SSIDs), for example “Guest”, “Staff” and “IoT”. To separate traffic, each SSID is mapped to a specific VLAN (802.1Q standard) configured on the access switch.
• Channel Planning: To avoid interference (Co-Channel Interference), adjacent cells must not use the same frequency.
  • 2.4 GHz: Only channels 1, 6 and 11 do not overlap. They should be alternated in a honeycomb pattern.
  • 5 GHz: Offers many more non-overlapping channels, reducing interference, but the signal penetrates walls less easily.
• Placement: APs should be installed preferably on ceilings, away from metallic structures or interference sources (microwave ovens, electric motors). A Site Survey must ensure a cell overlap of 15–20% for smooth roaming.

Wi-Fi Standards