Traffic Engineering Extensions for Enhanced DetNet

Introduction As defined in , Traffic Engineering (TE) is mainly focus on the control and optimization of routing and forwarding functions to steer traffic through the network. TE can deal with the issues with performance evaluation and performance optimization of operational IP networks and address the traffic oriented performance requirements including delay, delay variation, packet loss, and throughput while utilizing network resources. 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 QoS includes the bounded latency indicating the minimum and maximum end-to-end latency from source to destination and bounded jitter (packet delay variation). Three techniques are used by DetNet to provide these qualities of service including service protection, explicit routes and resource allocation. As per , DetNet can also be seen as a specialized branch of TE. The DetNet forwarding sub-layer provides resource allocations and explicit routes to guarantee the bounded latency, using existing TE mechanisms such as SR-TE, MPLS-TE and so on. But the enhanced DetNet is required to provide the packet treatment for data plane to achieve the DetNet QoS in large-scale networks. has described the enhanced requirements for DetNet enhanced data plane including the deterministic latency guarantees. has proposed the framework of enhanced DetNet data plane for packet treatment which should support new functions such as queuing mechanisms to ensure the deterministic latency. A common data fields can be defined as per and a Deterministic Latency Action (DLA) option has been proposed to carry DetNet-specific metadata. The existing TE mechanisms for resource allocations and explicit routes are not sufficient for enhanced DetNet. For example, the explicit routes should consider the queuing information when selecting and distributing the explicit path. And the resource management should be provisioned including the resource reservations and allocations. The TE mechanisms should consider the queuing-based or time-based resources. Moreover, as per , DetNet is required to maintain per-flow state information and provide resource reservation for individual flows. As discussed in , it should deal with large-scale dynamic deterministic flows and large-scale network topology in enhanced DetNet. It may be challenging for network operations in large-scale networks even if the flow aggregation may be supported. As discussed in , it may provide traffic scheduling instead of the flow scheduling and support the TE control at traffic-aggregate level than the per-flow or flow-aggregate level. Moreover, as per I-D.xiong-detnet-differentiated-detnet-aware-qos describes that multiple deterministic services may demand different set of SLAs and it should define more than one DetNet QoS levels according to different application scenarios. The TE mechanisms in enhanced DetNet should support the the Differentiated DetNet QoS of Multiple Services while utilizing network resources. As per , DetNet can also be seen as a specialized branch of TE. As it is required to provide enhancements for data plane in scaling networks, this document proposes a set of extensions for traffic engineering to achieve the differentiated DetNet QoS in enhanced DetNet.

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 . DD-TE: Differentiated DetNet-aware Traffic Engineering DT: Deterministic Class-Type TRC: Time-based Resources Container

Traffic Engineering for Differentiated DetNet QoS As per , DetNet can be viewed as a TE mechanism to achieve DetNet QoS. DetNet performs the per-flow or flow-aggregate scheduling in service sub-layer and uses resource allocations and explicit route mechanisms in forwarding sub-layer. And DetNet can be applied in existing TE data plane mechanisms such as IP, MPLS-TE and SR-TE. As the enhanced DetNet should support the differentiated DetNet QoS, the document proposes a set of extensions for traffic engineering to achieve differentiated DetNet QoS in enhanced DetNet called Differentiated DetNet-aware Traffic Engineering (DD-TE). DD-TE can be used to achieve multiple classes of deterministic services and optimize the resources utilization in scaling networks. The key elements required in DD-TE solution are as follows: 1. Policy As per , policy allows for the selection of paths (including next hops) based on information beyond basic reachability. The routing policy including bounded latency constraint-based routing can be considered when selecting and distributing the candidate paths. As per , deterministic routes can be established along the constraint-based paths within a Flex-Algorithm topology. As per , deterministic paths can be computed in PCE or controller with the deterministic latency constraints. As defined in , the BGP flowspec can be used to apply the DetNet flows mapping policy. 2. Path steering As per , path steering is the ability to forward packets using more information than just knowledge of the next hop. The per-flow or flow-aggregate scheduling is not applicable since it requires a large amount of control signaling to establish and maintain DetNet flows when it will be large-scale dynamic deterministic flows and large-scale network topology in scaling networks of enhanced DetNet. As discussed in , it may provide traffic scheduling in enhanced DetNet data plane and provide 4 DetNet traffic classes for Differentiated DetNet QoS. So the DD-TE mechanism should use the traffic class information to forward packets at traffic-aggregate level instead of the per-flow or flow-aggregate level. As per , in scaling networks of enhanced DetNet data plane, the enhanced QoS-related functions and metadata has been proposed to guarantee the bounded latency such as the queuing-based mechanisms and metadata. The deterministic latency information may be provided to forward packets for path steering. DD-TE can be applied in TE data plane such as IPv6 , MPLS and SRv6 . 3. Resource management As per , the resource management should support the time-based resource-aware control and forwarding including resource reservations and allocations. The time-based resource should cover the queuing and scheduling mechanisms based on the capability of end-to-end delay, jitter and loss. To guarantee the time-based resource, the resource control in layers model section 5 may be provided to avoid the conflict between DetNet flows to achieve differentiated DetNet QoS and high resources utilization.

Layers Model of DD-TE The resource control of DD-TE is important to regulate the traffic, deliver different levels of services and alleviate congestion issues to guarantee the bounded latency. It needs to resolve competition for network resources between traffic flows belonging to the same service class (intra-class contention resolution) and traffic flows belonging to different classes (inter-class contention resolution). This document proposes the layers model for enhanced DetNet control plane to configure the deterministic services to achieve differentiated DetNet QoS. The DetNet TE domains in control plane can be divided into three layers including deterministic links, deterministic paths and deterministic services as shown in Figure 1.

Deterministic Services:|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>| Deterministic Paths: +.............................................>+ +.............................................>+ Deterministic Links: O---------------->O O--------------->O O---------------->O O--------------->O O---------------->O O--------------->O +-----+ +-----+ +-----+ DetNet Domain: | A |--------------| B |--------------| C | +--+--+ +--+--+ +--+--+ The Layers Model of DD-TE has the following characteristics:

The deterministic links are designed to resolve resources competition among different traffic classes and provide deterministic forwarding capabilities at multiple levels.
The deterministic paths are designed to resolve resources competition among different paths within the same traffic class.
The deterministic services are designed to resolve resources competition among different flows on the same path.

Deterministic Links The deterministic links as defined in I-D.xiong-lsr-detnet-deterministic-links provide a one-dimensional deterministic metric to guarantee the deterministic forwarding capabilities at different levels. The deterministic link has the following attributes:

Link ID: an identifier that uniquely identifies a deterministic link within DetNet domain.
DT type: indicate the level of deterministic link.
MaxReservedBandwidth: the maximum bandwidth of the deterministic link.
TRC Parameters: carry the TRC ID and the capacity of the time-based resources which is reserved for the link.

Deterministic Paths When DetNet services with different SLA requirements requested to transmit, one or more deterministic paths may be calculated based on the deterministic links. The deterministic paths may be co-existed with the same DT and the time-based resources should be planned when each path is established. The deterministic paths has the following attributes:

Path ID: an identifier that uniquely identifies a deterministic path within DetNet domain.
DT type: indicate the level of deterministic link.
Source and Destination Nodes: indicate the head and end address of requested service.
Path Parameters: used to describe the result of deterministic paths including the seleted deterministic links and other information guiding deterministic forwarding behavior for each hop such as mapping function.
TRC Parameters: carry the TRC ID and the time-based resources which is planned for the path.

Deterministic Services The deterministic services may be configured to map the DetNet flows to the corresponding path. The deterministic services has the following attributes:

Service ID: an identifier that uniquely identifies a deterministic services on a deterministic path.
Service Level : the indicator of the service requirement.
Path ID: a deterministic path to deliver the service.
Policy: indicate the admission control and traffic policy for the DetNet flows within the same traffic class on the path.
TRC Parameters: carry the TRC ID and the time-based resources which is allocated for the traffic class.

Control Plane Extensions for DD-TE

+----------+ 3-Service Request-->|Controller|-->4-Deterministic Path Planning +---+--+---+ | ^ 2-Deterministic Links Resource Report | | | | | | 5-Path Distribution V | ................................................. . . . 1-Resoure Collection . . . Flow . +---+ +---+ +---+ . +---> . | A |------------| B |------------| C | . | . +---+ +---+ +---+ . | . DetNet Domain . | . . | . 6-Path Establishment and Resource Allocation . | . . | ................................................. | |-->7-Admision Control and Traffic Policy of Deterministic service

As described in , it is required to support the configuration of multiple queuing mechanisms. Different queuing mechanisms may be supported at different levels of latency, jitter and other guarantees. The enhancement for controller plane should be provided such as configuration information model as defined in .

And the type of queuing mechanism and the related queuing parameters should be advertised and configured. For example, the deterministic links with queuing resource could be distributed by IGP protocol as per and I-D.xiong-lsr-detnet-deterministic-link.

The deterministic routes may be loose routes in distributed scenarios. It is required to support the distributed deterministic routes which are established by distributed protocols such as IGP as defined in .

In scaling deterministic networks, it may across multiple network domains, it is required to support the inter-domain deterministic routes to achieve the end-to-end latency, bounded jitter. And the deadline of latency and jitter of each domain and segment should be determined and controlled. The inter-domain mechanism MUST be considered at the boundary nodes such as BGP configurations defined in and PCEP solution .

As defined in , the deterministic latency constraints can be carried in PCEP extensions and the end-to-end deterministic path computation should be achieved for DetNet service.

As defined in , the BGP flowspec can be used for the filtering of the packets that match the DetNet networks and the mapping between TSN streams and DetNet flows in the control plane.

Security Considerations TBA

IANA Considerations TBA

Acknowledgements TBA