SBI Message Priority Mechanism

The primary usage of SBI Message Priority (SMP) is to provide guidance to 5GC NF acting as HTTP/2 clients or servers while making throttling decisions related to overload control. The priority information may also be used for routing in the proxies. Eventually a server may use the priority information to process higher-priority requests before lower-priority requests. The SMP mechanism uses the "3gpp-Sbi-Message-Priority" custom HTTP header to set and carry the message priority between the client and the server. The custom HTTP header enforces the message priority end to end between the client and the server through one or more proxies.

The SMP mechanism uses the stream priority mechanism specified in IETF RFC 7540 [7] clause 5.3. The stream priority enforces the message priority at the HTTP/2 connection level not end to end. HTTP/2 clients, servers implementing SBIs must support the custom HTTP header and stream priority.

The header contains the HTTP/2 message priority value: The encoding of the header follows the ABNF as defined in IETF RFC 7230 [12].
3gpp-Sbi-Message-Priority = "3gpp-Sbi-Message-Priority" ":" (DIGIT / %x31-32 DIGIT / "3" %x30-31)
A message with
3gpp-Sbi-Message-Priority "0"
has the highest priority.
Example:
3gpp-Sbi-Message-Priority: 10

A client, proxy, and a server uses the "3gpp-Sbi-Message-Priority" value when setting or evaluating the priority of a message. The client assigns the request priority by adding the "3gpp-Sbi-Message-Priority" custom HTTP header to the message and setting its value. If the "3gpp-Sbi-Message-Priority" custom HTTP header isn’t present in a response message, then the HTTP nodes use the priority indicated in the "3gpp-Sbi-Message-Priority" of the associated request message. If the server wants to assign a different priority to the response message than the server assigns the response priority by adding the "3gpp-Sbi-Message-Priority" custom HTTP header to the message and setting its value.