The Signalling Bearer for NBAP (TS 25.433
) is a point-to-point protocol. There may be multiple point-to-point links between an RNC and a Node B. As shown in figure 1, the standard allows operators to choose one out of two protocol suites for transporting the NBAP messages.
The signalling bearer in the Radio Network Control Plane is SAAL-UNI (ITU-T Rec. Q.2100 ) over ATM. The protocols to be used to support NBAP signalling are SSCF-UNI (ITU-T Rec. Q.2130 ) on top of SSCOP (ITU-T Rec. Q.2110 ) and AAL Type 5 (ITU-T Rec. I.363.5 ).
SCTP (IETF RFC 2960 ) over IP shall be supported as the transport for NBAP signalling bearer on Iub Interface. A RNC equipped with the SCTP stack option shall initiate the INIT procedure for establishing association. The data link layer is as specified in chapter 4.2.
The checksum method specified in IETF RFC 3309  shall be used instead of the method specified in IETF RFC 2960 ().
An IP UTRAN node shall support IPv6 (IETF RFC 2460 ). The support of IPv4 (IETF RFC 791 ) is optional.
IP dual stack is recommended for the potential transition period from IPv4 to IPv6 in the transport network.
Each signalling bearer between the RNC and Node B shall correspond to one single SCTP stream in UL and one single SCTP stream in DL direction, both streams belonging to the same SCTP association.
IP Differentiated Services code point marking (IETF RFC 2474 ) shall be supported. The Diffserv code point may be determined from the application parameters.