L3 Managed Core Switch

Work out three numbers: ports, PoE budget and uplink speed. For ports, add one or two ports for the NVR and the uplink to the number of cameras and allow about 20% spare for growth; for 16 cameras a 24-port model fits. For power, assume 12 W per fixed camera (typically 6 to 16 W): 16 × 12 = 192 W at the cameras, divided by 0.85 for cable loss is about 226 W, and with 20% headroom about 271 W at the switch, so you need a PoE budget of roughly 300 W or more. Camera ports can be 100 Mbps for typical cameras, but the switch's link to the NVR should be Gigabit, and if you need VLANs or remote monitoring, choose a Lite-Managed or managed model. KDT examples are the KP-1606J3SFT (16 PoE ports, 400 W) if you do not plan to expand, and the KP-2408H4SMU (24 Gigabit PoE ports, 600 W) if you do.

An unmanaged switch has no settings page and works as soon as it is powered on; it is enough for a simple single-subnet network, for example the KP-0804H4SF, whose AI functions are selected with DIP switches. A Lite-Managed (Smart) switch has a web page and provides the basics such as VLAN, QoS, port mirroring, port rate limiting and PoE on/off; the KP-0406H4SLMT is an example. A managed switch adds a console and CLI to the web page and is needed for security, several VLANs, monitoring and larger networks; in the KDT range, the KP-2408H4SMU (Layer 2) and the KP-2404H5SM3U (Layer 3) are managed through the web interface, console, Telnet and SSH. As a rule of thumb: choose unmanaged if you only need PoE and connectivity, Lite-Managed if you must separate or monitor the network, and managed if you need security and full control.

A Layer 2 switch forwards frames only by MAC address inside one network (VLAN), which is enough to connect the cameras, the NVR and the computers of a single subnet. A Layer 3 switch also routes between different VLANs and subnets (Inter-VLAN Routing) at hardware speed, and larger models add static and dynamic routing. You need Layer 3 when you have several VLANs that must talk to each other (for example a camera VLAN and a VMS server VLAN), when the number of subnets is large, or when the switch sits in the network core. If you have only one subnet, Layer 2 is cheaper and simpler, and routing can be left to a router or firewall. KDT Layer 3 examples are the KC-2800H5SM3, the KP-4806H5SM3 and Carbon-series models such as the KS-C24G-T-6YQ.

In KP models the first two digits give the number of PoE ports and the next two digits the number of other (uplink) ports; for example the KP-0804H4SF has 8 PoE ports and 4 other ports, and the KP-2404H5SM3U has 24 PoE ports and 4 uplink ports. Fast Ethernet means all ports are 10/100 Mbps; Semi Gigabit means the PoE ports are 10/100 Mbps and the uplinks are Gigabit (some models also have one or two Gigabit PoE ports); Full Gigabit means every port is Gigabit; and 10 Gigabit means the model has 10 Gbps uplinks. PoE+ means the 802.3at standard with up to 30 W per port, Hi-PoE means a model with ports of up to 90 W under 802.3bt (on some models only the first few ports), AI means smart functions set with a DIP switch such as VLAN, Extend and Watchdog, and Lite-Managed means simple management through a web page. The prefix KP identifies PoE switches, KC core switches without PoE, and KS-C the Carbon series for data centers.

IEEE 802.3af (also called PoE or Type 1) delivers up to 15.4 W at the port (PSE) and at most 12.95 W reaches the device (PD); IEEE 802.3at (PoE+ or Type 2) delivers 30 W at the port and 25.5 W at the device; and IEEE 802.3bt, which is also marketed as PoE++ or Hi-PoE, delivers 60 W at the port and 51 W at the device in Type 3 and 90 W at the port and 71.3 W at the device in Type 4. The difference between the two figures is the power lost in the cable resistance, about 15% to 21% in the worst case of a 100 m cable, so compare a camera's consumption with the device-side (PD) figure, not the port figure. Standards af and at use two pairs of wires, bt can use all four pairs, and in every case the switch first detects and classifies the device and only then supplies power.