108
When implementing 10 or more cameras, the network load can be estimated using a few rules
of thumb:
> A camera that is configured to deliver high-quality images at high frame rates will use
approx. 2 to 3 Mbit/s of the available network bandwidth.
> With more than 12 to 15 cameras, consider using a switch with a gigabit backbone. If a
gigabit-supporting switch is used, the server that runs the video management software
should have a gigabit network adapter installed.
Technologies that enable the management of bandwidth consumption include the use of VLANs
on a switched network, Quality of Service and event-based recordings.
For more on these topics,
see chapters 9 and 11.
12.1.2 Calculating storage needs
As mentioned earlier, the type of video compression used is one of the factors affecting storage
requirements. The H.264 compression format is by far the most efficient video compression
technique available today. Without compromising image quality, an H.264 encoder can reduce
the size of a digital video file by more than 80% compared with the Motion JPEG format and as
much as 50% more than with the MPEG-4 (Part 2) standard. This means much less network
bandwidth and storage space are required for an H.264 video file.
Sample storage calculations for all three compression formats are provided in the tables below.
Because of a number of variables that affect average bit rate levels, calculations are not so clear-
cut for H.264 and MPEG-4. With Motion JPEG, there is a clear formula because Motion JPEG
consists of one individual file for each image. Storage requirements for Motion JPEG recordings
vary depending on the frame rate, resolution and level of compression.
H.264 calculation:
Approx. bit rate / 8(bits in a byte) x 3600s = KB per hour / 1000 = MB per hour
MB per hour x hours of operation per day / 1000 = GB per day
GB per day x requested period of storage = Storage need
Table 12.1a The figures above are based on lots of motion in a scene. With fewer changes in a scene, the figures can
be 20% lower. The amount of motion in a scene can have a big impact on the amount of storage required.
Camera
Resolution
Approx. bit rate
(kbit/s)
Frames per
second
MB/
hour
Hours of
operation
GB/day
No. 1
CIF
110
5
49.5
8
0.4
No. 2
CIF
250
15
112.5
8
0.9
No. 3
4CIF
600
15
270
12
3.2
Total for the 3 cameras and 30 days of storage = 135 GB
CHAPTER 12 - BANDWIDTH AND STORAGE CONSIDERATIONS
