Only when the control and media flow traverse NAT, can people use private IP address to make sessions with SIP protocol.

要让使用私有ip地址的用户通过SIP协议进行会话，就必须使SIP的信令流和媒体流穿越NAT，而其中的难点是媒体流的穿越。

youdao

Though TRUN can traverse symmetrical NAT, it causes network delay because packet needs to transmit through TRUN server.

TRUN虽然能够穿越对成型的NAT，但由于报文要通过TRUN服务器转发，这又增加了网络延迟。

youdao