Flow Aggregation for Enhanced DetNet

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. The DetNet Quality of Service (QoS) includes the bounded latency indicating the minimum and maximum end-to-end latency from source to destination and bounded jitter (packet delay variation). 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. As per , flow aggregation is the ability to aggregate individual flows with and their associated resource control into a larger aggregate. DetNet flow aggregation may be enabled for the flows with the same or very similar QoS and CoS characteristics via the use of wildcards, masks, prefixes, and ranges. As per , two methods of flow aggregation have been proposed such as aggregation via LSP hierarchy and aggregating DetNet flows as a new DetNet flow. In scaling networks, as per , the enhanced DetNet should support that different levels of applications co-existed with different SLAs requirements. From the use cases in and , DetNet applications differ in their network topologies and specific desired behavior. DetNet flows should be transmitted and forwarded with different DetNet QoS behaviors. It should provide fine-grained service provisioning to achieve differentiated DetNet QoS. The DetNet flows with the same level of services requirements can be aggregated to receive corresponding treatment and forwarding behaviour. The DetNet flows can be classified and aggregated based on flow-specific characteristics. Moreover, the existing aggregation of individual flows may be still challenging for network operations. The aggregated flows still requires a large amount of control signaling to establish and maintain the states of DetNet flows when it will be large-scale dynamic deterministic flows and network topology in enhanced DetNet. It is required to improve the scalability and forward packets at class-aggregate level instead of the per-flow or flow-aggregate level and the flow identification of aggregated-class can be used to indicate the per-hop behavior without the maintain of the states in scaling networks. This document describes the flow aggregation scenarios and proposes a method by aggregating DetNet flows based on DetNet flow-specific classification in enhanced DetNet and the flow identification of aggregated-class can be used to indicate the required treatment and forwarding behaviors in scaling networks.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Terminology The terminology is defined as . DC: DetNet Traffic Class

Flow Aggregation Scenarios in Enhanced DetNet

Aggregating DetNet Flows across Different Network Domains The flow aggregation may be required in multi-domain scenario to achieve the end-to-end QoS guarantees and the aggregated flows may across multiple domains. As per , different network implementations may be intended for different application domains, where there is no additional requirements for the coordination. As defined in [ITU-T Y.2122], the network operating parameters of a flow aggregate should be exchanged among different network domains. As shown in Figure 1, the DetNet domain B receiving aggregated flow should identify the flow and get the service requirements such as the QoS parameters of the flow aggregate.

+-----------------+ +-----------------+ | | | | Individual Flows | DetNet Domain A | Aggregated Flow | DetNet Domain B | ---------------->| | --------------> | | +-----------------+ +-----------------+

Aggregating DetNet Flows to Provide Fine-grained QoS Behaviors As per , different levels of applications differ in the SLAs requirements such as tight jitter, strict latency, loose latency and so on. The individual flows demand differentiated DetNet treatment and QoS forwarding behaviors. And the DetNet node or domain providing multiple forwarding technologies needs to transmit the individual flows by aggregating the flows to a selecting treatment solution with corresponding per-hop QoS behavior as shown in Figure 2. For example, as per , the 5GS as a logical DetNet node or nodes needs to get the service requirements and service level of the aggregated flows to provide fine-grained per-hop behaviors.

Aggregating DetNet Flows without Maintaining States at Transit Nodes As per , the treatment solutions in data plane can be categorized based on performance and functional characteristics. For example, the solution can be categorized based on traffic granularity such as flow aggregate and class level. The class level is provided to simplify the control and accommodate traffic fluctuations by aggregating flows with the same level of service requirements. The flow aggregation based on the class level could further improve the scalability. As per , it may have the large number of traffic flows in scaling network and it is impossible for per-flow state identification. As shown in Figure 3, the flow identification of aggregated-class can be used to indicate the required treatment and forwarding behaviors without the maintain of the states at transit nodes.

+-------------+ +-------------+ +-------------+ Aggregated| | Aggregated| | | | Flows|DetNet Node A| Flows|DetNet Node B| |DetNet Node N| --------->| |---------->| |----->...| | +-------------+ +-------------+ +-------------+

Aggregating DetNet Flows on Aggregated-class Level When DetNet flows are aggregated on aggregated-class level, transit nodes provide deterministic services to the aggregate and on a per-class scheduling without the states maintaining. The nodes performing aggregation should ensure all per-flow service requirements within the class are achieved. For example, the latency or jitter bounds of a class aggregate should not exceed bounds of the individual flows. The aggregation based on the class level has data plane and controller plane aspects. For the data plane, when DetNet flows are aggregated to a class, transit nodes provide service to the aggregate and not on a per-DetNet-flow basis. And the transit nodes supporting this type of aggregation should identify the class of the aggregated flows and ensure that individual flows receive the corresponding traffic treatment and forwarding behaviour. For the controller plane, the service should be provisioned on an aggregated-class level. The resources should be controlled and scheduled on a per-class basis and the routes should be established to meet the service requirements with the allocated resources. The edge nodes must be able to handle admission control for DetNet flows to an aggregated class based on the available resources.

Flow Classification The DetNet QoS can be achieved by aggregating flows based on DetNet flow-specific traffic classification and providing the traffic-forwarding treatment. The flow classification should consider the flow-specific characteristics such as traffic specification and service requirements. For example, the DetNet flows MAY be classified based on the service SLAs requirements of applications in scaling networks as per . And the services can also be classified into tight/loose latency, large/small burst, periodic/non-periodic and large/small scale services as per . Several classes can be predefined to indicate the different levels of applications with SLAs requirements and each class demands differentiated QoS behaviors and treatment as well as different DetNet capabilities in scaling networks.

Flow Identification The flow identification is required to be dynamic and simplified to ensure the aggregated flows have compatible DetNet flow-specific QoS characteristics. For the data plane, individual flows may be aggregated for treatment based on shared service specification on aggregated-class level which identified by an aggregation class (A-Class). The nodes should provide the class level traffic treatment based on A-Class. The aggregation class information may be used alone or together with other metadata to indicate the required queuing and forwarding behaviors. The encoding of the A-Class may reuse the DSCP/TC or existing field such as the TC field in A-Label as per . And it also can be encapsulated with the deterministic latency information as per .

Security Considerations TBA

IANA Considerations TBA

Acknowledgements TBA