Primary Rate Interface is used in the telecommunications industry to send voice and data transmissions over the Integrated Services Digital Network (ISDN). ISDN gives you better call quality and enables the transmission of data by making use of packet switched networks.
Session Initiation Protocol (SIP) is a protocol used to create and terminate real-time sessions between two or more parties over an IP network. SIP sessions can involve the transmission of multimedia including video, voice, or other communications but are often used to deliver phone calls over the internet, commonly referred to as Voice over IP (VoIP).
