When selecting the appropriate switch in low-voltage engineering (such as network, security, and communication systems), it is essential to consider project requirements, performance parameters, budget, and future scalability. Below are the key steps and considerations:

I. Define the Requirements and Scenario

1. Application Scenarios:
   • Security Monitoring: Needs to support PoE power supply (e.g., cameras) and high-bandwidth video transmission.
   • Office Network: Needs stability, support for VLAN segmentation, and QoS (to ensure voice/video priority).
   • Industrial Environments: Requires industrial-grade switches that are resistant to high temperatures, dust, and electromagnetic interference.
   • Data Centers: Needs high-density, high-throughput, low-latency 10G/40G switches.
2. Number of Devices:
   • Determine the number of ports based on the number of devices (e.g., cameras, APs, computers) and reserve 20%-30% extra for future expansion.

II. Selection of Core Parameters

1. Port Types and Speeds:
   • Speed:
     • For basic devices (e.g., cameras, printers): 100Mbps (Fast Ethernet).
     • For high-definition video, NAS, servers: 1Gbps (Gigabit Ethernet) or higher.
   • Fiber/Ethernet Ports:
     • For long-distance transmission (>100 meters), use fiber optic ports (SFP modules).
     • For short distances, use RJ45 Ethernet ports.
2. PoE Requirements:
   • If powering APs or cameras via PoE, choose a PoE-enabled switch and pay attention to:
     • PoE Standards: 802.3af (15.4W), 802.3at (30W), 802.3bt (60W/90W).
     • Total Power Budget: Ensure the total power consumption of all PoE devices does not exceed the switch’s PoE budget.
3. Performance Parameters:
   • Backplane Bandwidth: At least double the sum of all port speeds. For a 24-port Gigabit switch, it should have at least 48Gbps of backplane bandwidth.
   • Packet Forwarding Rate: For Gigabit ports, it should be 1.488Mpps per port. A 24-port Gigabit switch should have at least 35.7Mpps.
   • MAC Address Table: Large networks require a larger MAC address table (e.g., 16K or more).

III. Features and Protocols

1. Management Features:
   • Unmanaged Switches: Plug-and-play, suitable for simple networks (e.g., small-scale monitoring).
   • Managed Switches: Support for VLAN, STP, QoS, port mirroring, etc., suitable for complex networks.
   • Layer 2/Layer 3 Switches:
     • Layer 2: For MAC address-based forwarding, suitable for general networking.
     • Layer 3: Supports IP routing, suitable for communication across subnets (e.g., enterprise internal network segmentation).
2. Security Features:
   • 802.1X authentication, ACL access control, port isolation, anti-ARP spoofing, etc.

IV. Reliability and Scalability

1. Hardware Redundancy:
   • Dual power supplies and fan redundancy (critical for environments like server rooms or hospitals).
   • MTBF (Mean Time Between Failures) should be as high as possible (industrial-grade switches >100,000 hours).
2. Scalability:
   • Stacking Function (e.g., Cisco StackWise, Huawei iStack) enables logical unified management of multiple switches.
   • Modular Switches (e.g., chassis switches) support flexible card-based upgrades.

V. Brand and Budget

1. Brand Selection:
   • High-end: Cisco, HPE Aruba, Juniper (for enterprise-grade core networks).
   • Mid-range: Huawei, H3C (high cost-performance).
   • Entry-level: TP-Link, D-Link (for small projects or tight budgets).
2. Budget Allocation:
   • Core Layer > Aggregation Layer > Access Layer. High-performance models are recommended for core switches.

VI. Installation and Environment

1. Physical Size:
   • Rack-mounted (19-inch standard rack) or desktop-mounted (for small deployments).
   • Industrial switches should meet IP30/IP40 protection levels.
2. Heat Dissipation and Noise:
   • Fan-cooled for server rooms, and fanless, silent models for office environments.

VII. Typical Scenario Recommendations

VIII. Pitfalls to Avoid

1. Avoid False Advertising:
   • Some switches labeled as “Gigabit” may not have sufficient backplane bandwidth (e.g., only 10Gbps), causing congestion when multiple ports are fully loaded.
2. PoE Power Trap:
   • A switch labeled “24-port PoE” but with a total power budget of only 180W may not provide full power to each port.
3. Compatibility Issues:
   • Non-standard PoE (e.g., “PoE+”) may damage devices. Ensure the PoE standard matches with terminal devices.

By following these steps and considering the specific needs of the project, low-voltage engineers can make informed choices that balance performance, cost, and reliability. For large projects, it is recommended to set up a test environment to verify switch performance.