Comparison Dahua NVR2108-8P-4KS2 vs Dahua NVR2108HS-8P-4KS2

The maximum data transfer rate supported by the DVR's LAN ports.

Note that for simple tasks, a rather modest by modern standards speed of 100 Mbps is often enough. However, high bandwidth ( 1 Gbps) not only simplifies the transfer of large amounts of data, but also helps to reduce lags and improve the overall quality of communication; and modern technologies make it possible to provide support for gigabit LAN even in fairly simple and inexpensive registrars.

Of course, in order to use all the features of the LAN, it is necessary that the devices connected to such ports also support the appropriate speeds.

The highest resolution in which the recorder can record video when a signal is received from all channels simultaneously. If cameras are not connected to some channels, the recording resolution may be higher (see “Maximum Resolution”).

Higher resolution has a positive effect on detail, but takes up more space and requires more computing power for processing, which accordingly affects the price of the registrar.

The highest frame rate in the recorded video that the recorder can support when recording from all available channels simultaneously. If not all channels are occupied by cameras, this figure may be higher.

The minimum required for comfortable viewing is 24 fps. And in the most modern video standards, the frame rate can be much higher — 50 – 60 fps. Higher values result in better quality and smoother video that allows you to clearly see fast movement; however, such video takes up more space and requires powerful hardware, which affects the price of recorders.

Standards (codecs) used by the recorder to compress the recorded video.

This parameter is important when viewing recorded materials on another device — for example, a media centre, into which a "flash drive" with files from the recorder is inserted. For normal viewing, it is necessary that the player supports the appropriate codec — otherwise the video will be displayed with distortion or will not work at all. Technical details on various standards can be found in special sources.

Note that if you plan to view the materials on a computer, you can not pay much attention to this parameter: most modern operating systems have extensive built-in sets of codecs, and if you don’t have the right codec, you can easily find it on the Internet.

The PoE (Power over Ethernet) technology itself allows you to transmit not only data, but also energy to power network devices via an Ethernet network cable. And the presence of PoE output(s) makes it possible to power such devices from the network connectors of the recorder. This eliminates the need to lay additional wires or use independent power supplies, which can be especially important for some equipment, such as external IP surveillance cameras. And when using so-called splitters - devices that separate the PoE cable signal into purely network data and supply power - using such outputs you can also power equipment that does not initially support PoE (the main thing is that their power characteristics match the capabilities of the switch).

As for PoE standards, they determine not just the overall power supply, but also compatibility with specific devices: the consumer must support the same standard as the recorder, otherwise normal operation will be impossible. Nowadays, including in switch connectors, you can find two types of such standards - active ( 802.3af, 802.3at, 802.3bt) and passive (one is called that). The main difference between these varieties is that active PoE provides for matching the power source and load in terms of voltage and power; passive PoE does not have such functions, and energy is supplied “as is”, without adjustments. Here is a more detailed description of speci...fic standards:

- 802.3af. The oldest active PoE power format in use today. Provides power output power up to 15 W (at the consumer input - up to 13 W), output voltage 44 - 57 V (input - 37 - 57 V) and power in a pair of supply wires up to 350 mA. Despite its “venerable age”, it still continues to be widely used; so there are still quite a lot of recorders that work only with 802.3af on sale (as of the end of 2021). However, it is worth considering that this standard covers 4 so-called power classes (from 0 to 3), differing in the maximum number of watts at the output and input. So when using 802.3af, it doesn't hurt to make sure that the output power is sufficient for the selected load.

- 802.3af/at. A combination of two standards at once - the 802.3af described above and the newer 802.3at. The latter allows you to supply power up to 30 W to the output (up to 25.5 W at the input of the powered device), uses a voltage of 50 - 57 V (42.5 - 57 V at the input), while the power in a pair of wires does not exceed 600 mA. This combination is relatively inexpensive, but it makes it possible to power a wide variety of external devices; so at the end of 2021, it is this type of PoE output that is most popular among recorders.

— 802.3af/at, bt. A combination of 802.3af/at described above with the 802.3bt standard (PoE++, PoE type 3 or type 4). 802.3bt is the newest of the PoE power formats; Unlike earlier ones, it uses not 2, but 4 power wires, which allows you to supply very significant power to external devices - up to 71 V (with 90 W at the power output). Such capabilities can be indispensable when supplying energy to equipment with high consumption - for example, external surveillance cameras, supplemented by heating systems. On the other hand, support for the 802.3bt standard significantly affects the cost of the recorder, and such a connection places special demands on the quality of the cables. In addition, you need to keep in mind that this standard also includes the UPoE format, created by Cisco and used in its equipment; and this standard (it is known as PoE type 3) has a more modest power - up to 60 W at the output (up to 51 W at the consumer input). And the general 802.3bt standard includes two power classes - class 8, in which maximum performance is achieved, and class 7, where 75 W is supplied to the output and about 62 W reaches the consumer. So if you plan to use 802.3bt equipment, when choosing a recorder from this category, you must make sure that the power supply is sufficient for the normal operation of the connected devices.

- Passive. As already mentioned, the key difference between passive PoE and the active standards described above is that in this case the power output produces a strictly fixed power, without any automatic adjustments or adjustments for a specific device. The main advantage of this standard is its low cost: its implementation is much cheaper than active PoE, so such ports can be found even in entry-level recorders. On the other hand, the aforementioned lack of auto-tuning makes it much more difficult to coordinate equipment with each other - especially in light of the fact that different devices can differ significantly in the output/consumed voltage and power (power). Because of this, when using passive PoE, you need to pay special attention to the compatibility of the source and load in these parameters. If there is no match, then in the best case (if the voltage/power at the output is lower than required) the power simply will not work, and in the worst case (if there is excess voltage/power) there is a high probability of overloads, overheating and even breakdowns with fires - and such troubles may not occur immediately, but after quite a considerable time. And you definitely cannot connect devices with active inputs to passive PoE outputs - for the same reasons.

The maximum power that the DVR is capable of delivering per PoE output.

Such outputs are described in detail above; just briefly recall that they are Ethernet network ports, supplemented by the ability to power connected equipment directly over the LAN cable, without additional wires. As for the power of such a supply, it must correspond to the characteristics of the connected equipment; however, the term "compliant" may have different meanings depending on the PoE standard being used (see "PoE (output)").

So, if the registrar and the equipment work according to one of the active standards (802.3af, 802.3at, 802.3bt), the output power of the switch must not be lower than the power consumption of the connected equipment. At the same time, exceeding the output power is not scary — the described standards provide automatic adjustment, which allows the powered device to receive exactly as much power as needed, without overloading. But if the output is not powerful enough, it is obvious that it simply cannot provide effective work.

In turn, when using passive PoE, the output power of the power supply should ideally match the power consumption of the load as closely as possible. This is due to the fact that in such cases the power output produces a strictly defined power, with little or no matching and adjustment. And if the excess of a couple of watts, most powered devices are able to transfer more or less "calmly", then a more significant exces...s is fraught with overloads, overheating and equipment failure.

In conclusion, it should be said that if there are several PoE ports and they are used simultaneously, the available power supply per port can be noticeably less than when PoE is operating in only one connector. This point can be clarified by information on the total PoE power (see below) — this power is divided into all the ports involved. For example, if the switch has three PoE outputs, and the power per output is 60 W, then the total power can also be claimed at 60 W. Accordingly, when using PoE on all three outputs at once, the power on each of them will be less than 60/3 = 20 W. Technically, more advanced methods of power management are also possible — with "smart" power distribution depending on the needs of specific devices (relatively speaking, 30 W, 20 W and 10 W for the same total value of 60 W); but for a full guarantee, it is worth proceeding from the fact that all energy is divided equally.

The total power that the NVR is capable of delivering to all PoE outputs.

See above for details on such exits; here we only recall that the general idea of PoE is to supply power over the same Ethernet cable that transmits data. The total power is given for models in which there are more than one such connectors; it allows you to estimate the total power consumption of all PoE devices that can be connected to the NVR at the same time.

There are two important things to keep in mind when choosing a specific value. First, when multiple ports operate, the energy is usually shared equally among them; at the same time, the total power of the registrar does not always correspond to the sum of the maximum powers of all PoE outputs. For example, a model with 8 ports of 30 W each may have a total figure of not 240 W (8 * 30 W), but only 100 W. In fact, this discrepancy means that with the simultaneous use of all connectors, each of them will be able to deliver not 30 W, but a maximum of 100/8 = 12.5 W. The second point is that the total power consumption of the load should ideally be no higher than 75% of the claimed total PoE power — this provides an additional guarantee in case of malfunctions.