IPv6 Option for Scaling Deterministic Networks

Introduction According to , Deterministic Networking (DetNet) operates at the IP layer and delivers service which provides extremely low data loss rates and bounded latency within a network domain. DetNet data planes has been specified in . As described in [RFC9320], the end-to-end bounded latency depends on the value of queuing delay bound along with the queuing mechanisms. Multiple queuing mechanisms can be used to guarantee the bounded latency in DetNet. But the existing deterministic technologies are facing large-scale number of nodes and long-distance transmission, traffic scheduling, dynamic flows, and other controversial issues in large-scale networks. The DetNet enhanced data plane is required to support a data plane method of flow identification and packet treatment. has described the enhancement requirements for DetNet enhanced data plane, such as aggregated flow identification and deterministic latency guarantees. The enhanced QoS-related functions and metadata should be provided in scaling networks. has discussed the data plane enhancement solutions and queuing mechanisms in DetNet. New DetNet-specific metadata should be carried in data plane such as IP and SRv6 data plane. This document outlines how the DetNet-specific metadata are encapsulated in IPv6 and specifies formats and principles for the IPv6 DetNet Options to provide deterministic services.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Abbreviations and definitions used in this document:

SRH:: Segment Routing Header
SRv6:: Segment Routing for IPv6 forwarding plane
DL:: Deterministic Latency
CSQF:: Cycle Specified Queuing and Forwarding
TQF:: Timeslot Queuing and Forwarding
C-SCORE:: Work Conserving Stateless Core Fair Queuing
EDF:: Earliest Deadline First
TAS:: Time Aware Shaper
ATS:: Asynchronous Traffic Shaping
CQF:: Cyclic Queuing and Forwarding
FQ:: Fair Queuing
TSN:: Time-Sensitive Networking
ECQF:: Enhanced Cyclic Queuing and Forwarding
gLBF:: guaranteed Latency Based Forwarding

Terminology The terminology is defined as .

Enhancement Requirements for Scaling Deterministic Networks

As per , the DetNet data plane must support the aggregation of DetNet flows in order to support larger numbers of DetNet flows and improve scalability by reducing the per-hop states. And the flow aggregation may be necessary for scaling networks. As per , the deterministic services may demand different deterministic QoS requirements according to different levels of application requirements. For example, industrial applications may demand tight jitter, strict latency limit requirements. The video applications may demand relative loose latency requirements and so on. The flow identification with service-level aggregation and explicit aggregated flow identification should be supported. The flow identification is required to be dynamic and simplified to ensure the aggregated flows have compatible DetNet flow-specific QoS characteristics. In DetNet MPLS, A-Label defined as per can be added explicitly to the packets. But in other DetNet data plane, no aggregated flow specific information is available. The aggregation identification and service type should be defined as the DetNet-specific metadata. The DetNet nodes along the path can identify the aggregated flow to achieve the end-to-end QoS in scaling networks.

As described in , the end-to-end bounded latency depends on the queuing delay bound and the queuing mechanisms. Multiple queuing mechanisms have been proposed such as TAS [IIEEE802.1Qbv], CBS [IEEE802.1Q-2014],ATS [IEEE802.1Qcr], CQF [IEEE802.1Qch] and so on. In scaling networks which has large variation in latency among hops, great number of flows and multiple domains, has described the technical requirements for enhanced data plane solutions. Many variations and extensions of queuing mechanisms have been proposed to resolve the scalability issues in DetNet. has described the classification criteria of the solutions. For instance, the CQF variations for cyclic-based scheduling includes the ECQF [IEEE 802.1Qdv], Multi-CQF , TCQF and CSQF . The TAS variations for timeslot-based scheduling includes TQF . The FQ variations for rate-based scheduling includes C-SCORE ATS [IEEE802.1Qcr] and gLBF . The EDF variations for deadline-based scheduling includes EDF and Local Deadline . The Damper variations for damper-based scheduling includes Damper and gLBF . And when queuing mechanisms used in large-scale networks, the per-flow states can not be maintained with scalability issues. Some queuing parameters should be carried for coordination between nodes so as to make appropriate packet forwarding and scheduling decisions to meet the time bounds. As per , the information used by functions ensuring deterministic latency should be supported as such queuing-based information. And queuing mechanisms and solutions require different information to help the functions of ensuring deterministic latency, including regulation, queue management. The deterministic latency metadata should be defined for forwarding nodes along the path which can apply the queuing mechanisms and get the related deterministic latency metadata in packet to achieve the end-to-end bounded latency.

The DetNet Options This document defines new IPv6 options for DetNet to signal DetNet-specific metadata. The DetNet options helps to discriminate the types of mechanisms and specify the related parameters. The format of the DetNet options follow the generic definition in section 4.2 of . The DetNet options may be placed either in an HbH (Hop-by-Hop) or a DoH (Destination Option Header) EH (Extension Header).

The Aggregation Option helps to identify the aggregated flow and discriminate the different deterministic QoS requirements and specify the related parameters.

Service Type: 8-bit unsigned integer, indicates the service-level or class-based aggregation type of packet treatment ensuring the deterministic QoS as following shown. This type can also indicate the aggregated class.

Service Type Flag: 8-bit flags field. Aggregation ID: 32bits. It provides explicit and unique identifier for aggregated flow identification. DetNet nodes performing aggregation using aggregation ID. End-to-end Delay Budget: 32bits. It provides the value of end-to-end delay budget for the aggregated flow. End-to-end Delay Variation Budget: 32bits. It provides the value of end-to-end delay variation budget for the aggregated flow.

Deterministic Latency Option The Deterministic Latency Option helps to discriminate the deterministic latency technologies and specify the related parameters.

Deterministic Latency Option Format Option Type: TBD1, 8-bit option type identifier indicates the Deterministic Latency Option. Option Data Len: 8-bit unsigned integer. Length of this option, in octets, not including the first 2 octets. DL (Deterministic Latency) Type: 8-bit unsigned integer, indicates the type of deterministic latency information and related queuing and scheduling metadata. Flag: 8-bit flags field. Deterministic Latency Data: Variable-length field and the data is specific to the type. The Deterministic Latency type and data should depend on and align with the classification of the data plane queuing and scheduling solutions as per . For instance, it may cover the information such as cycle, timeslot, deadline, rate, packet size, damper, timestamp information as shown in Figure 3.

Deterministic Latency Type and Information

Encapsulation of DetNet Options

IPv6 Networks The DetNet Options is intended to be placed in an IPv6 HbH EH since it must be processed by every DetNet forwarding node along the path. For the DetNet options, all DetNet forwarding nodes can use the queuing information to achieve the packet forwarding and scheduling. The format of DetNet options in IPv6 is as follows.

DetNet Option Format in IPv6

SRv6 Networks The DetNet Options is intended to be placed in an DOH EH before an SRH since it must be processed by the DetNet forwarding nodes of the SRv6 segment list. For the DetNet options, the DetNet forwarding nodes among SRv6 segment list can use the queuing-based information to achieve the packet forwarding and scheduling. The format of DetNet options in SRv6 is as follows.

DetNet Options Format in SRv6

Security Considerations As this document describes new options for IPv6, it can apply the security considerations of and . Security considerations for DetNet are covered in the DetNet Architecture and DetNet data plane , , and DetNet security considerations . The security considerations specified in are also applicable to the procedures defined in this document.

IANA Considerations

New Option for IPv6 This specification updates the "Destination Options and Hop-by-Hop Options" under the "Internet Protocol Version 6 (IPv6) Parameters" registry with the values below:

Type	Description	Reference
TBD1	IPv6 Aggregation Option	[this document]
TBD2	IPv6 Deterministic Latency Option	[this document]

Acknowledgements The authors would like to thank Aihua Liu, Peng Liu, Bin Tan, and Shaofu Peng for their review, suggestions and comments to this document.