Outer Header Format

The SMF sends the Outer Header information element (IE) to the UPF. The Packet Detection Rule (PDR) of Packet Forwarding Control Protocol (PFCP) session includes this IE. The Outer Header IE is present in the N4 Session Establishment Request message sent over the Sx interface. The version 16.4.0 of 3GPP TS 29.244 specification defines the format of this IE.

The following table identifies the encoding format of Outer Header Creation Description field. It takes the form of a bitmask where each bit indicates the outer header to be added to the outgoing packet. Note that the SMF ignores the spare bits.

Header Encoding Format
Octet / Bit Outer Header Created in the Outgoing Packet
5/1 GTP-U/UDP/IPv4
5/2 GTP-U/UDP/IPv6
5/3 UDP/IPv4
5/4 UDP/IPv6
5/5 IPv4
5/6 IPv6
5/7 C-TAG
5/8 S-TAG
6/1 N19 Indication
6/2 N6 Indication
6/3 TCP/IPv4
6/4 TCP/IPv6

NOTES:

  • Currently, the UP or UPF does not support the following values of Outer Header Creation Description:

    • IPv4

    • IPv6

    • C-TAG

    • S-TAG

    • N19 Indication

    • N6 Indication

  • The third and fourth bits of sixth Octet (that is, 6/3 and 6/4) are spare bits (that is, not part of 3GPP TS) used for LI over TCP.

Important

The SMF and the UPF must support the same format of Outer Header IE for a successful session establishment.