Managing Bandwidth for IP Surveillance Networks
1. Overview
When it comes to bandwidth utilization in a network, IP cameras have a dramatic effect on the overall bandwidth. Camera bit rate is directly correlated to the bandwidth and storage of the camera network. Understanding the cameras’ bit rate usage is crucial when designing a network that includes IP cameras.
2. Factors
There are many factors that determine the bit rate for an IP camera streaming on the network. For the sake of simplicity, this paper will cover the relationship between resolution, frame rate, and bit rate. Other factors not covered here (not exhaustive) can include:
- Compression methods
- I-frame intervals
- Level of activity and motion in a scene
- Lighting conditions
- Rate control options such as constant and variable
3. What is Bit Rate?
Bit rate is equal to the data rate. This contributes to the network bandwidth usage and also storage, if video is being recorded. Bit rate is always measured as number of bits per second. With modern cameras, the primary stream will always be measured in megabits per second (Mb/s). A megabit is equal to million bits.
1 Byte (1B) is equal to 8 bits (8b). Note the capitalization of the letter for a Byte. Using the same formula, then an 8Mb/s stream would be equal to a 1MB/s stream. If a camera was recording at 1MB/s constantly, the video would take up 60MB in one minute, 600MB in ten minutes, and so forth.
Below is an example of what a low bitrate image would look like compared to a high bitrate image
Higher bitrate images contain more data, so they have higher quality or are more detailed.
4. What is Resolution?
Resolution for video is determined by multiplying the number of pixels in the height of an image by the number of pixels in the width of the same image. The higher the number of pixels, the higher the resolution.
In relation to the size of a display, the bigger the display, the more real estate that the number of pixels need to be spread across that display. Going from a full HD (1080p) resolution to a 4K resolution on a smartphone display would be more difficult to distinguish than on a television screen.
For video, resolution can be looked at as the “capacity” or the size of the “window”. It is related to the quality of the image, which is covered later in this article, but it does not solely determine the quality.
Below is an example of different resolutions for the same scene 
5. What is Frame Rate?
Frame rate is the number of frames or “windows” per unit of time. Normally, the unit of time is one second. The common terminology for frame rate is “FPS” or “frames per second”.
A higher frame rate catches more frames within a second. This results in a smoother video in an environment with fast moving objects. Below is an example of a lower frame rate video compared to a high frame rate video. 
In this scene, we can see that much more of the motion is captured within that single second with the higher frame rate video.
6. Balancing
There is a common misconception that resolution is the only factor is determining the “quality” of a video image. The reality is that all 3 factors – resolution, frame rate, and bitrate - must be balanced together to determine the optimal setting for the network. Some factors to consider:
- Storage capacity of the surveillance system
- Network bandwidth capacity
- Recording method – continuous, scheduled, event-based, etc
- Level of activity in the scene
- How much detail to capture within the scene
If resolution is constant, raising the bitrate would increase the quality of the image. Example:
If bitrate stays constant, raising the resolution would actually decrease the quality of the image. A 4K video has 4 times the number of pixels compared to a 1080p video. So, in that case, in order to have the same image quality, the bitrate for the 4K video would need to be 4 times higher than the bitrate for the 1080p video.
Moreover, one must remember that bitrate is the amount of data within the time period, which is one second normally. So that bitrate gets divided by the number of frames within that second. So, if bitrate is constant, increasing the frame rate would decrease the image quality. In order to have the same image quality, a 30fps video would need to have double the bitrate compared to a 15fps.
In taking all three factors into consideration, a balance must be struck to get desired outcomes for the situation without overloading the network and video storage.
For example, if the level of detail for smaller objects in the image is not crucial, perhaps the resolution for the main stream in the camera can be set to a lower value, decreasing the bitrate that is needed.
If there is a scene that does not have too much activity, the frame rate can be lowered, therefore decreasing the bitrate that is needed to maintain the image quality.
7. Impact of IP Video on the Network
Market trends have shown that camera resolutions greater than 5MP are rapidly growing in usage. Most notably, this would be 4K resolution cameras. Camera burst data shows that for 4K cameras, the burst bitrate at any given point for a 4K camera would exceed the bandwidth allocated to fast ethernet, which would be a max of 100Mbps. (more on video bursting here: What's the Right Amount of Bandwidth for your Network to Support Video? | EtherWAN USA)
Below is a chart showing how much bitrate would be needed to support different resolutions with bursting factored in. Because the effective bandwidth is always less than the theoretical maximum, a 4K camera with bursting would produce a bitrate that exceeds the bandwidth for fast ethernet. Therefore, gigabit capability is needed to handle 4K cameras. 
8. Wrap-up
Resolution, frame rate, and bitrate are the key elements in determining the quality of the video. They also affect the network bandwidth. Finding the right balance is essential in ending up with video with acceptable quality but is also appropriate for the network.
Depending on camera resolution and bitrate, gigabit speeds may be needed to support the required bandwidth. EtherWAN Systems, a leader in networking devices and applications for critical infrastructure, offers a full line of PoE (Power over Ethernet) switches with gigabit speeds to support 4K cameras and above.
Go here for more information: Hardened PoE Switches | EtherWAN USA
