WCS supports DTLS 1.2 handshake while establishing WebRTC connections, this protocol version is enavkled by default. However, DTLS 1.0 is also supported for compatibility. Obsolete protocol support can be forced for all the clients using the following parameter in flashphoner.properties file
dtls_force_version_0=true
Or it can be switched per browser according to User Agent string that clients sends during handshake since build 5.2.399
User Agent strings should be listed in dtls0_ua file which is placed to /usr/local/FlashphonerWebCallServer/conf folder, for example
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0 Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0
DTLS handshake errors can be written to dtls-error.log file which is placed to /usr/local/FlashphonerWebCallServer/logs folder
17:15:42,889 ERROR DtlsError - Stun-Clbk-thread udp//192.168.0.111:31016 User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0; alert level: 2; alert description: 40; message: null
To do this, the following settings should be added to log4j.properties file
log4j.logger.DtlsError=error, dtlsErrorAppender
log4j.additivity.DtlsError=false
log4j.appender.dtlsErrorAppender=org.apache.log4j.DailyRollingFileAppender
log4j.appender.dtlsErrorAppender.DatePattern='.'yyyy-MM-dd-HH
log4j.appender.dtlsErrorAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.dtlsErrorAppender.layout.ConversionPattern=%d{HH:mm:ss,SSS} %-5p %20.20c{1} - %t %m%n
log4j.appender.dtlsErrorAppender.File=${com.flashphoner.fms.AppHome}/logs/dtls-error.log
These settings will be added by default if WCS is cleanly installed, but the log4j.properties file is not overwritten when WCS is updated. In this case, the settings should be added manually
User-agent string from dtls-error.log should be added to dtls0_ua file, for example
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0 Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0 Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0
DTLS 1.0 will be used while WebRTC connection is establishing with the browsers listed above