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This section describes accessory tools that can be used to manage the WCS server.

Port routing checking

The WCS server may be behind NAT and as such it will require a port range opened for the external network, for instance, UDP 31000-32000.
This means that a UDP packet sent from the external network to the port in that range should reach the server where WCS is placed.

Hence, we have a simple test. Send a UDP packet from outside using nc and receive it on the server using tcpdump.
If the packet reached, the port is open.


echo -n "hello" | nc -4u -w1 31000

or for Debian:

echo -n "hello" | nc -u -w1 31000

This command sends a simple UDP packet in the given direction.


tcpdump udp port 31000

This command makes the server listen for a particular port and immediately outputs information about packet arrival to the console:

17:50:21.932509 IP myhost.39194 > host.31000: UDP, length 5

jstack tool

This is Java utility that provides important information about a Java process and execution threads.
When you run jstack from the console, a brief information about jstack is shown:

If the information is not shown or the jstack utility is not found, use the installation instruction to latest version of JDK. After installing jdk you should create a symbolical link to jstack to quickly run it:

ln -sf /usr/java/default/bin/jstack /usr/bin/jstack


jstack 8888 >

Here, 8888 is the ID of the Java process.

Since build 5.2.801, WCS is running from 'flashphoner' user for security reasons. Therefore, jstack should be launched from the same user if using JDK 8:

sudo -u `ps -o uname= -p $(pgrep java)` `which jstack` `pgrep java`

Testing channel bandwidth using iperf

A stream published picture quality depends on channel bandwidth between publisher and server, the same for subscriber. Channel bandwidth can be checked using iperf utility. This program is implemented for all major OS: Windows, MacOS, Ubuntu/Debian, CentOS. iperf in server mode can be installed and running with WCS, that allows to check whole channel bandwith from publisher to viewer.

iperf can be installed on CentOS 7 as follows:

yum install iperf3

Run iperf in server mode

iperf3 -s -p 5201

where 5201 is iperf port for testing client connections

On client side iperf can be launched as follows:

1. To test upload channel bandwith via UDP (Windows example)

iperf3.exe -c -p 5201 -u


  • - WCS server
  • 5201 - iperf port to connect

The result of the command above should look like this:

2. To test download channel bandwidth via UDP

iperf3.exe -c -p 5201 -u -R


  • - WCS server
  • 5201 - iperf port to connect

The result of the command above should look like this:

By default, iperf tests the channel for 10 seconds. This interval should be increased, for example, to 120 second

iperf3.exe -c -p 5201 -u -t 120

The upload channel bandwidth test via UDP result shows the maximum video publishing bitrate without packet losses. In the sample above bitrate should be limited with 1000 kbps, on server side for example


Note that iperf major versions on server and on testing client should be the same. Today version 3 is actual, but ther is also version 2 in repositories.