Both gNB and ng-eNB can be connected to the 5GC over the NG interface.
The transport layer for data streams over NG is an IP based Transport. The following Figure shows the transport protocol stacks over NG.
The GTP-U (TS 29.281
) protocol over UDP over IP shall be supported as the transport for data streams on the NG interface. The data link layer is as specified in clause 4
The transport bearer is identified by the GTP-U TEID (TS 29.281
) and the IP address (source TEID, destination TEID, source IP address, destination IP address).
The GTP-U (TS 29.281
) protocol shall be used over the NG-U interface toward the 5GC.
The path protocol used shall be UDP (IETF RFC 768
The UDP port number for GTP-U shall be as defined in TS 29.281
The NG-RAN node and the 5GC shall support fragmentation and assembly of GTP packets at the IP layer.
The NG-RAN node and the 5GC shall support IPv6 (IETF RFC 8200
) and/or IPv4 (IETF RFC 791
There may be one or several IP addresses in the NG-RAN node and in the 5GC. The packet processing function in the 5GC shall send downstream packets of a given PDU Session to the NG-RAN node IP address (received in NGAP) associated to that particular PDU Session. The packet processing function in the NG-RAN node shall send upstream packets of a given PDU Session to the 5GC IP address (received in NGAP) associated to that particular PDU Session.
The Transport Layer Address signalled in NGAP messages is a bit string of
32 bits in case of IPv4 address according to IETF RFC 791; or
128 bits in case of IPv6 address according to IETF RFC 8200; or
160 bits if both IPv4 and IPv6 addresses are signalled, in which case the IPv4 address is contained in the first 32 bits.
IP Differentiated Services code point marking (IETF RFC 2474
) shall be supported. The mapping between traffic categories and Diffserv code points shall be configurable by O&M based on 5QI, the Priority Level (if explicitly signalled), and other NG-RAN traffic parameters (e.g. ARP). Traffic categories are implementation-specific and may be determined from the application parameters.