8.Features
© 2023 China Daheng Group, Inc. Beijing Image Vision Technology Branch 166
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. The recommended maximum packet size is 8192 bytes, which can
improve the network transmission performance.
1)
When the packet size is set to more than 1500, 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
d a t a
= ( Size
p k t
× 8bits ) ⁄ Speed
l i n k
The time of packet delay is:
T
d e l a y
= Delay
p k t
⁄ 125,000,000
Among them: the Size
pkt
is packet size, Delay
pkt
is packet delay, BandW
reserve
is reserved bandwidth,
Speed
link
is link speed.
Effective network bandwidth:
BandW
avial
= ( Size
pkt
× 8bits ×
（
1
-
BandW
reserve
）
/ ( T
data
+ T
delay
)
Example 1: The packet size is 1500, the packet delay is 1000, the reserved bandwidth is 20%, and the
link speed is 1Gbps.
The time to transport a single stream packet is:
T
d a t a
= (1500 × 8 ) ⁄ 10 00,000,000 = 12
μs
The time of packet delay is:
T
d e l a y
= 1000 ⁄ 125,00 0,000 = 8
μs
The effective network bandwidth is:
Band
W
a v i a l
= (1464 × 8 × (1 -0.2 )) ⁄ (12
μs
+ 8
μs
) = 468
Mbps
