Liaison statement
LS on 3GPP 5G System acting as a Detnet node

1. Overall Description:
3GPP SA2 is working on extensions to the 5G System Time Sensitive
Communications (TSC) framework for the support of IETF’s DetNet deterministic
networking framework in a Study Item titled “Extensions to the TSC Framework to
support DetNet” as documented in SP-211633.

With respect to IETF DetNet specifications, the study makes the following
assumptions:

- The study considers 5GS (5G system) acting as a DetNet node in the DetNet
domain. - The study only considers the IP case, MPLS is not in the scope. - The
study considers the DetNet forwarding sub-layer related functions that are
applicable to the 5GS. For the IP case according to RFC 8939 section 1, no
service sub-layer function needs to be defined.

The 5GS DetNet node has interfaces towards the fixed network (N6 interface in
5GS) and on each User Equipment (UE) in the user plane. It is able to forward
IP packets between any of its interfaces. It is connected to the DetNet
Controller for centralized configuration. The 5GS DetNet node exposes
information about its interfaces and neighbour nodes to the Controller. The 5GS
DetNet node receives DetNet configuration including flow identification and QoS
requirements from the DetNet Controller.

The 3GPP SA2 would like to ask IETF DetNet WG guidance on the following points:

A)      DetNet YANG data model currently only includes end-to-end QoS
requirements for the DetNet flow such as max-latency and max-loss. On the other
hand, the 5G DetNet node needs to be aware of the max-latency and max-loss
requirements specific to the node.

1. Is there any work chartered in the IETF to determine the node specific
traffic requirements?

2. One approach considered in 3GPP has been to extend the DetNet YANG data
model in such a way that it can contain the node specific requirements as well.
Would this approach be very specific to 3GPP and 5GS DetNet node in which case
it would be appropriate for the 3GPP to standardize the required YANG model
extension, or would this be of more general interest for IETF DetNet
deployments so that the standardization should take place in the IETF? Where
possible 3GPP prefers a generic approach defined by IETF.

B)      3GPP is considering to specify to the possibility for reporting the 5GS
node, interface and neighbor information to DetNet controller to help build up
the network topology information. The reported information may include the
DetNet node ID, the list of interfaces (including their IP address and prefix),
and when applicable, the list of neighbouring nodes and other information. Has
IETF any feedback on 3GPP DetNet exposing its  interface and IP configuration
information as defined in RFCs 8343 and 8344 respectively, and on potentially
exposing  route information from 5GS Detnet Note as defined in RFC 8349? Does
IETF Detnet plan to recommend  any specific protocols between Detnet Nodes for
topology discovery (similar to LLDP in Layer 2 TSN Networks ) or is it meant to
be subject to deployments?

Is there any other information (e.g. Detnet Node capabilities) that is required
by DetNet to be reported to the DetNet controller?

Please Note that 3GPP is going to do the normative work in Q1 2023 about 5G
System Time-Sensitive Communications (TSC) framework for the support of IETF’s
DetNet and thus would need IETF guidance (in Q4 2022) about whether IETF plans
to do further work on these aspects in 2023.

2. Actions:
To IETF "Deterministic Networking (detnet)" WG:

ACTION: SA2 kindly asks IETF "Deterministic Networking (detnet)" WG to take the
above information into account and to provide any feedback.

3. Date of Next TSG-SA WG2 Meetings:

             DATES                LOCATION           CTRY
SA2#153e    October, 10-14th      Elbonia            Any (e-meeting)
SA2#154     November, 14-18th     To be determine    To be determined