SIP port, UDP protocol, generally the default is 5060. IPPBX registers an IP external line with IMS (generally it is given the SBC address +SIP port at the upper end of IMS). If it is a private network given by the operator, it is no problem. If the device is connected through a public network, the local SIP port of the device must be changed to a non-default port to prevent network attacks, piracy and other hidden dangers after port scanning.