SIP PRACK (Provisional Response Acknowledgement). Overview. There are two types of responses defined by SIP. They are provisional and final.
One problem with the original SIP specification was that it provided no method for the recipient of a request to know if it’s provisional responses have reached their destination when using an unreliable transport such as UDP. The ability to make these provisional responses reliable is defined by RFC 3262 “Reliability of Provisional Responses in SIP”. This reliability works by using the same SIP reliability mechanisms as final responses to an INVITE transaction.
SIP Provisional Response
When using reliable provisional responses, these responses are retransmitted by the UAS in response to an INVITE until a PRACK is received from the UAC. If the PRACK is acceptable to the UAS, the UAS would then respond with a 200 OK to the PRACK. In this instance the PRACK serves the same role as an ACK in a normal INVITE transaction. However, unlike the ACK, PRACK has its own response. A call flow of an INVITE transaction using reliable provisional responses can be seen below.
More Information
- SIP and WebRTC
- VoIP Software
- VoIP Design
- Session Initiation Protocol (SIP)
- SIP Analog Modem Server (SAMS)
- SIP Software Modules
- SIP Conferencing
- SIP Message Routing
- SIP Presence and Instant Messaging
- SIP Registration
- SIP User Authentication
- Secure SIP
- Session Initiation Protocol (SIP) and Deep Packet Inspection (DPI)
- SIP Trunking
- SIP Agents
- SIP Servers
VOCAL Technologies has been in business for over 30 years and is an engineering design house that can provide a custom solution that meets your unique communication requirements.
Please contact us to discuss your communication application requirements.