SIP (Session Initiation Protocol) is an Internet protocol for Internet telephony signaling. It is used by desk telephones with RJ45 jacks. SIP is supported by most mobile apps for making calls over a data connection. SIP is also used by doorphones that communicate over LAN or WiFi.

SIP supports mobility, instant messaging and online presence services. The advantage of SIP is its simplicity; however, it does not, for example, ensure line quality when making calls.
By default, SIP uses the UDP port 5060. It can also work over TCP/5060. The first version of this protocol was described in RFC 2543, the current second version is described in RFC 3261.
In context of NETIO products
SIP support is currently provided at experimental level in NETIO 4x.
NETIO smart sockets can act as a SIP VoIP telephone and for example react to incoming calls.
If you need to use SIP in NETIO 4x products in your project, please contact us.