Box, rack, and frame are not three mutually exclusive levels. “Rack” mainly explains how the device is installed; “frame” mainly explains whether the inside can be expanded by inserting and removing boards. A fixed-port switch can be installed in a rack, and a frame switch can also be installed in a rack. When selecting a model, look separately at installation dimensions, hardware architecture, service capacity, and maintenance requirements. Do not judge performance only by chassis size.
First separate two questions: where it is placed, and whether boards inside can be replaced
Think of a switch as a station responsible for sorting packages. Network ports are the entrances and exits, and the switching chip sends Ethernet frames to the appropriate port according to the destination address. The chassis determines whether the device can be placed on a desktop, fixed to a DIN rail, or installed in a cabinet, but it does not directly determine how much data it can handle. A compact switch may have high-speed uplinks, and an older device with a large size may have only 100 Mbit/s ports. Therefore, “a large chassis must be fast” and “a rack switch must be a core switch” are not reliable conclusions.
What is usually called a box switch is a complete unit with its main functions in a compact chassis, and its ports and main circuits are mostly fixed configuration. Common desktop, wall-mounted, and DIN-rail types may all use this structure. When new devices at a site exceed the number of ports, it is often necessary to add a switch or change the model rather than directly insert a new service board. Some fixed-configuration devices have replaceable power supplies or fans, but this does not automatically turn them into frame switches.
A rack switch means equipment suitable for installation in a standard cabinet, commonly with a 19-inch installation width and 1U height. 1U is about 44.45 mm and refers to the height unit occupied in the cabinet, not a unit of communication performance. The dimensions to check include not only height but also device depth, mounting ear position, rail or bracket requirements, and the space for power supplies and cables to extend. You cannot assume that any cabinet can be installed just because it says “1U.”
A frame switch uses a modular structure of chassis plus boards and may be equipped with control boards, service boards, switch fabric boards, power supplies, and fan modules. Which components are independent and which support redundancy or hot swapping must be based on the specific model’s manual. Its value is expanding according to business needs, replacing locally failed components, and, when the corresponding design is present, reducing the impact of a single point of failure. It is not that more slots are always more suitable for every project.
Calculate performance clearly: port rate does not equal usable service capacity
For example, a site needs to connect 24 Gigabit terminals and uplink through two 10-Gigabit optical ports. First confirm whether the terminals continuously send data at the same time, then check whether the uplink can bear the aggregated traffic. In an extreme case, 24 Gigabit ports may send nearly 24 Gbit/s of data to the uplink; if there is only one 10 Gbit/s uplink, when continuous total traffic exceeds its usable capacity, queuing will occur, and in severe cases packets will be dropped. Whether two uplinks can jointly carry the business also depends on link aggregation, traffic distribution, and network design. You cannot simply think that plugging in two cables gives any single service 20 Gbit/s.
Switching capacity and packet forwarding rate are two other indicators. Switching capacity is often expressed in Gbit/s and indicates the throughput capability of the switching system; packet forwarding rate is expressed in packets per second, and small-packet scenarios may reach the forwarding capability earlier. When manufacturers calculate switching capacity, they may add the two directions of port transmission and reception. Before comparing parameters, confirm that the measurement basis is the same. For frame devices, also check board capability, slot bandwidth, switch fabric board configuration, and whether the installed board combination is oversubscribed.
For beginners, the most practical order is: first list the number of terminals and port types, then estimate concurrent traffic, then determine uplink and redundancy requirements, and only finally decide the chassis form. A large number of cameras does not necessarily mean frame equipment is required; when traffic is controllable and ports are sufficient, a fixed-configuration rack switch may be simpler. Conversely, for an aggregation node that will need to expand many service boards in the future, evaluate the slots, power supply, and spare parts cost of a modular chassis in advance.
A cabinet is not just about screwing the device in: heat, cables, and power supply also need design
Before installation, check the ambient temperature allowed by the device and distinguish between room temperature and the intake air temperature inside the cabinet. After the cabinet door is closed, the temperature around the device may be higher than room temperature. Fan-equipped devices must organize intake and exhaust airflow in the specified direction, and devices with different front-to-back airflow must not draw hot air into each other; fanless industrial devices also need to meet natural heat dissipation spacing, and side ventilation slots must not be pressed tightly against the cabinet wall. Industrial grade does not mean that temperature rise, dust, or humidity can be ignored.
Cables should enter a cable management frame, leaving insertion and removal clearance at ports to avoid the weight of network cables pulling on sockets. Fiber optic cables in particular must comply with the bending radius specified by the cable manufacturer, and must not be bent at a right angle through a cabinet door gap. The routing of power cables and communication cables should be handled according to project specifications. Heavy frame chassis may require brackets or dedicated slide rails and cannot rely only on the two front mounting ears to bear the weight.
Two power supply modules also do not mean the power supply path is fully redundant. If both modules are plugged into the same power strip that may lose power, a power strip failure will still cut power to the entire device. Check whether a single power supply can bear the entire device load, whether the power supply paths are independent, and the alarm when a power supply fails. Hot swapping can also only be performed according to the manufacturer’s instructions. Do not directly pull out a board carrying live traffic just because the module has a handle.
Three site questions to help you decide
There are only a few PLCs in a control cabinet. Which type should be chosen?First look at DIN-rail installation, power supply voltage, temperature, interference resistance, and required protocols. A small fixed-configuration industrial switch is usually more convenient; whether it is managed and whether it supports redundancy should be decided according to network requirements.
What about a standard cabinet connecting dozens of terminals?You can first evaluate a fixed-configuration rack switch and check the number of ports, optical uplinks, VLAN management, power budget, and heat dissipation. If PoE is included, the overall switching capability and power supply capability must be calculated separately, and you cannot look only at the number of network ports.
What if a central node plans to add interface types over the long term?Consider whether a frame type can expand through boards, and check redundancy of the control and switching planes, upgrade paths, spare parts supply, and maintenance downtime windows. Modularity increases procurement, configuration, and operations complexity, so do not buy it just for being “large and complete.”
Final acceptance should include port negotiation, actual throughput, full-load temperature rise, uplink failure, power supply failure, and recovery tests. Recording the test conditions and actual board configuration in the report is more valuable than writing only “rack type has good performance.” The device appearance and airflow diagrams in this article are schematic. Specific specifications, insertion and removal conditions, and installation methods are subject to the purchased model’s documentation.
Translated from the Chinese technical article. Source first published: 2020-01-15. Source last revised: 2026-10-13T23:36:13+08:00. Read the Chinese source
