Nq-AP: This application layer protocol supports the APN information retrieval procedure between the RCAF and the SGSN.
Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 .
Editor's note: The protocol stack will be added once Stage 3 has selected the protocol type to use between S4-SGSN and RCAF. It is up to Stage 3 to decide whether the same or different protocols will be used for the Nq' interface to the Gn/Gp-SGSN and the S4-SGSN, respectively.