8.Features
© 2023 China Daheng Group, Inc. Beijing Image Vision Technology Branch 122
11)
The camera's acquisition frame rate
In addition to the maximum allowable bandwidth of the network and the time limit for camera acquisition,
the exposure time can also affect the frame rate. For example: for MARS-2621-42GTM/C camera, when
the exposure time is 200ms, the corresponding frame rate is 5fps.
In conclusion, the frame rate of the camera takes the minimum of the maximum allowable frame rate of
the network, the acquisition frame rate and the exposure frame rate.
8.5.2.
Stream Channel Packet Size
Stream channel packet size (SCPS) refers to the network packet's size of the stream channel data which
is transferred to the host terminal by the camera, in bytes and the default value is 1500. It includes the IP
header, UDP header and GVSP header which the total length is 36 bytes, so the payload in the default
channel network packet is 1464 bytes. When the link speed is 10Gbps, 5Gbps or 2.5Gbps, the
recommended maximum SCPS can be set to 8164 bytes, which can improve the network transmission
performance.
1)
When the packet size is set to more than 1500 bytes, it needs the network equipment such
as network card and switch to support the jumbo frames.
2)
When changing the packet size, the packet size and the packet delay will affect the network
transfer performance together.
8.5.3.
Stream Channel Packet Delay
The stream channel packet delay (SCPD) is used to control the bandwidth of the image streaming data of
the camera. The packet delay is the number of the idle clocks that inserted between adjacent network
packets transmitted in the stream channel. Increase the packet delay can reduce the camera's bandwidth
usage, and it may also reduce the camera's frame rate (the camera frame rate also depends on the
exposure time, camera acquisition time).
The camera's packet size, packet delay and reserved bandwidth determine the effective network
bandwidth. The effective network bandwidth is calculated as follows:
The time required to transmit a single stream packet:
T
data
=
(
Size
pkt
×
8 bits
)
Speed
link
⁄
Effective network bandwidth:
BandW
avial
=(Size
pkt
×8bits×(1-BandW
reserve
)/(T
data
+T
delay
)
Among them: the Size
pkt
is packet size, Delay
pkt
is packet delay, BandW
reserve
is reserved bandwidth,
Speed
link
is link speed.
Example 1: The packet size is 1500, the packet delay is 1000, the reserved bandwidth is 20%, and the
link speed is 10Gbps.
The time to transport a single stream packet is:
