9 Interworking with DN (Unstructured)

29.5613GPP5G SystemInterworking between 5G Network and external Data NetworksRelease 17Stage 3TS

9.1 General

When support of unstructured PDU type data is provided at the N6 interface, different Point-to-Point (PtP) tunneling techniques may be used. When using PtP tunneling by UDP/IPv6 encapsulation clause 9.2 below shall be followed. Other techniques as described in clause 9.3 below may be used.

In the following clauses, the AS is used as an example for the destination in the external DN.

9.2 N6 PtP tunnelling based on UDP/IP

N6 PtP tunnelling based on UDP/IPv6 may be used to deliver unstructured PDU type data to the AS.

The PtP tunnel is set up by configuration of tunnel parameters in both end of the tunnel. The following parameters are pre-configured in the UPF per DNN:

– the UDP destination port number to use when sending unstructured PDU type data;

– the UDP port number it wants to receive unstructured PDU type data;

– the destination IP address to be used for sending unstructured PDU type data.

The following is pre-configured in the AS:

– the UDP destination port number to use when sending unstructured PDU type data;

– the UDP port number it wants to receive unstructured PDU type data.

NOTE 1: The UPF as well as the AS can use any UDP port numbers not assigned by IANA. The port numbers used need to be aligned between peers.

IP address allocation procedures for the UE (i.e. PDU session) are performed by the SMF as described in clause 6.3.2, but the IPv6 prefix is not provided to the UE, i.e. Router Advertisements and DHCPv6 are not performed. The SMF assigns a suffix (i.e. IPv6 Interface Identifier) for the PDU session. For the N6 PtP tunnel, the IPv6 prefix allocated for the PDU session plus suffix assigned for the PtP tunnel is used as source address for the uplink data and as destination address for the downlink data.

During the PDU session establishment, the UPF associates the GTP-U tunnel for the PDU session with the N6 PtP tunnel.

The UPF acts as a transparent forwarding node between the UE and the AS.

For uplink delivery, if the uplink data is received from the GTP-U tunnel, the UPF shall forward the received data to the AS over the N6 PtP tunnel associated with the GTP-U tunnel with the destination address of the AS and the configured UDP destination port number for unstructured PDU type data.

For downlink delivery, the AS shall send the data using UDP/IP encapsulation with the IPv6 prefix plus suffix as destination address and the configured UDP destination port number for unstructured PDU type data.

NOTE 2: The UPF decapsulates the received data (i.e. removes the UDP/IPv6 headers) and forwards the data on the GTP-U tunnel identified by the IPv6 prefix of the UE (i.e. PDU session) for delivery to the UE.

Figure 9.2-1: Protocol configuration for unstructured PDU type data (user plane) using N6 UDP/IPv6 PtP tunneling

9.3 Other N6 tunnelling mechanism

N6 PtP tunnelling mechanisms such as PMIPv6/GRE, L2TP, etc, may be used to deliver unstructured PDU type data to AS. The general handling of such delivery mechanisms is as described below.

A PtP tunnel is established by the UPF towards the AS. Depending on the type of protocol employed on the N6 PtP tunnel, the N6 PtP tunnel setup may be done at the time of PDU Session establishment or at the time of first MO datagram being sent by the UE. The UPF selects the AS based on its configuration (e.g. per DNN, or per PtP tunnel type, etc). However, IP address allocation procedures for the UE (according to clause 6.3.2) are not performed by the SMF.

NOTE: An AS can be dedicated for handling a specific protocol for unstructured PDU type data.

The UPF acts as a transparent forwarding node between the UE and the AS.

For uplink delivery, the UPF forwards the received data to the AS over the established N6 PtP tunnel.

For downlink delivery, the AS locates the right N6 PtP tunnel for the UE (using information such as UE identifiers in the unstructured PDU type protocol itself, etc) to forward the data. The AS sends the data to UPF over the established N6 PtP tunnel. The UPF in turn sends the data on the GTP-U tunnel identified by the associated N6 PtP tunnel for delivery to the UE.