20
Connection / Installation
●
Ensure that there is sufficient network bandwidth
for the data volume to be sent out by VN-C20.
●Data volume to be sent by VN-C20 varies
with the settings and number of distributions.
●
The maximum bit rate from VN-C20 is about 9 Mbps.

Estimation of total bit rate

The JPEG file size per frame varies with the
encoding settings as well as input video signals.
The following table may be used as a reference.
When VFS is selected, the quantization table
during JPEG encoding will be maintained and the
file size will increase/decrease according to the
input signals. When AFS is selected, encoding will
be performed such that the target file size is the
average size of multiple JPEG images.
VN-C20 accepts requests from up to a maximum of
5 clients. In addition, it also allows transmission of 1
multicast stream. The total frame rate refers to the
sum of these frame rates.
For example, when 10 fps is requested by 2
clients, and in addition multicast is transmitted at
a rate of 10 fps, the total frame rate will be:
10 + 10 + 10 = 30 fps
If the JPEG file size per frame is 30 KB, then the
total bit rate will be:
30 KB
⳯
30 fps = 900 KB/s = Approx. 7.2 Mbps

Insufficient network bandwidth

When there is insufficient bandwidth, the number
of JPEG frames (frame rate) that the client can
acquire will decrease.

Network Delay

When the client acquires JPEG via TCP, VN-C20 will
send out data while checking the ACK from the client
at the same time. For networks with considerable
delay, data cannot be sent out until ACK is received,
and therefore the frame rate will drop.
Network delay due to a drop in frame rate can be
eliminated by receiving data via multicast.

Network Jitter

When there is considerable network jitter, delay
time may be prolonged and the image frame rate
may drop.

Packet Loss

When acquiring images from VN-C20 via TCP,
packet loss may be recovered by resending from
TCP. When there is considerable delay during
resending, however, missing data may occur and
the image frame rate may drop.
When packet loss occurs during multicast sending
from VN-C20, the image frame rate may drop.

List of protocols and port numbers used

by VN-C20

VN-C20 uses the protocols and port numbers
listed below. Ensure that these ports are allowed
through the firewall when a firewall is to be
installed.
Network Requirements
Picture Quality
Control Method
VGA
File Size
QVGA
File Size
VFS
(Variable
File Size)
1 (High) 80 KB 27 KB
260 KB 20 KB
340 KB 13 KB
4 (Medium)
30 KB 10 KB
525 KB 8 KB
620 KB 7 KB
7 (Low) 15 KB 5 KB
AFS
(Average File Size)
Selection
may be
made from
the range
between 10
to 100 KB
Selection
may be
made from
the range
between 3
to 33 KB
Protocol / Port
No. Purpose of Use
TCP/80 JPEG acquisition, Web
Settings page, API
TCP/20, 21 FTP
TCP/25 Mail delivery
TCP/User Setting No.
Alarm sending
UDP/User Setting No.
Alarm sending
UDP/User Setting No.
Multicast sending
VN-C20_EN.book Page 20 Tuesday, February 14, 2006 10:51 AM