Enhanced DetNet Data Plane (EDP) Framework for Scaling Deterministic Networks

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 framework of DetNet data planes has been specified in . The IP and MPLS DetNet data plane has been defined respectively in and . The DetNet IP data plane primarily uses 6-tuple-based flow identification. And the DetNet MPLS data plane leverages existing pseudowire (PW) encapsulations and MPLS Traffic Engineering (MPLS-TE) encapsulations. The applications in 5G networks demand much more deterministic and precise properties in large-scale networks. 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 Enhanced DetNet (EDN) is required to provide the enhancement of flow identification and packet treatment and support the enhanced functions or mechanisms for DetNet to achieve the DetNet in large-scale networks. The Enhanced DetNet Data Plane (EDP) is required to support a data plane method of flow identification and packet treatment. has described the service requirements and characteristics of scaling deterministic networks and analyzes the existing technologies gap for EDP especially applying the DetNet data plane as per . has described the enhancement requirements for EDP. The EDP aims to describe how to use IP and/or MPLS, and related OAM, to support a data plane method of flow identification and packet treatment over Layer 3. The enhanced QoS-related functions and metadata should be provided in scaling networks. For example, as described in , 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. New DetNet-specific metadata should be carried in EDP such as IP/MPLS/SRv6 Data Plane. This document proposes the enhancement of packet treatment to support the functions and metadata for Enhanced DetNet Data plane (EDP). It describes related enhanced controller plane considerations as well.

The terminology is defined as and .

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:

EDN:: Enhanced DetNet or Enhanced Deterministic Networking
EDP:: Enhanced Data plane
IPv6:: IP version 6 forwarding plane
SRv6:: Segment Routing for IPv6 forwarding plane

As defined in , the DetNet data plane describes how application flows, or App-flows are carried over DetNet networks and it is provided by the DetNet service and forwarding sub-layers with DetNet-related data plane functions and mechanisms. From charter and milestones, the enhanced DetNet data plane is required to provide the enhancement of flow identification and packet treatment including the enhanced QoS-related functions and metadata in scaling networks.

This section proposes the enhancement for the DetNet Data Plane Protocol Stack as shown in Figure 1 and the enhanced DetNet-related data plane functions and mechanisms should be provided by the DetNet service and forwarding sub-layers.

From the perspective of differentiated services requirements in section 3.1.1, a scaling network needs to provide the deterministic service for various applications. And the deterministic service may demand different DetNet QoS levels according to different application scenarios. The DetNet data plane should support the identification of multiple flows and the differentiated deterministic QoS for each DetNet flow. According to the gap described in section 3.3.1, this document proposes the enhanced DetNet data plane to support flow identification of DetNet differentiated services with service-level identification. It may downscale the network operations with a large number of deterministic flows and network nodes in scaling networks.

As discussed in section 3.3.2.1, it may be challenging to compute the best path to meet all of the requirements and the the paths vary with the real-time change of the network topology in scaling networks. The explicit routes may be not appropriate for scaling networks. This document propose the deterministic routes which can be strict explicit paths or loose routes. The former is applicable to centralized scenarios with controllers, and the latter is applicable to distributed scenarios.

As discussed in section 3.3.2.1, it may be challenging to compute the best path to meet all of the requirements within a scaling network topology pool including multiple network metrics. This document proposes the deterministic links to provide a one-dimensional deterministic metric to guarantee for the deterministic forwarding capabilities at different levels. The computing end-to-end delay bounds is defined in . It is the sum of non-queuing delay bound and queuing delay bound in DetNet bounded latency model. The upper bounds of queuing delay depends on the queuing mechanisms deployed along the path. For example, a link with a queuing mechanism that does not guarantee a bounded delay a non-determinisitc link and a link with a queuing mechanism that can provide deterministic delay is called a deterministic link. The delay of a a deterministic link is consist of the propagation delay of the packet on the link and the queuing delay of the packet at the node. A deterministic link can be a sub-network that provides deterministic transmission or a Point-to-Point (P2P) link. The deterministic links could be distributed by IGP protocol as per .

As per , technical gaps are existing in multi-domain DetNet scenarios. As discussed in section 3.3.2.1, the inter-domain deterministic routes need to be established and provisioned in multi-domain scenarios. The stitching of the intra-domain paths should be considered in DetNet data plane. In the centralized scenario, when the source and destination PEs of a deterministic service are located at the two ends with a limited physical range, one controller (single domain) or multiple controllers (cross domains) compute one or more paths with deterministic SLA according to the typical Traffic Specification (T-SPEC) based on the collected deterministic resources, or compute dynamically according to the service T-SPEC as required by the services. In the distributed scenario, deterministic loose routes are computed on the device through routing protocols. Interior Gateway Protocol (IGP) is used to compute deterministic routes based on deterministic-delay inside a domain, and Border Gateway Protocol (BGP) is used to compute deterministic routes based on accurate delay/jitter across domains.

As discussed in section 3.3.2.2, the reservation and allocation of queuing related resources or deterministic latency resources should be taken into consideration in DetNet data plane. The networks need to shield the differences between network capabilities. Deterministic resource is the basis for providing deterministic network services. It refers to the resources that meet the deterministic indicators of a node and link processing as well as the corresponding resource processing mechanisms (such as link bandwidth, queues, and scheduling algorithms). It is required to make unified modeling for all the deterministic resources. The deterministic links are provided and distributed to support the deterministic resource and forwarding capabilities. As discussed in section 3.1.2, it is necessary to make overall resource planning and scheduling for the network to achieve the high-efficiency of resources utilization when provide multiple DetNet services. The admission control policy of a flow should take into account the deterministic resource.

As dicussed in section 3.3.2.3, it is required to support the enhancement of queuing mechanisms. Multiple queuing mechanisms can provide different levels of latency, jitter and other guarantees. The DetNet forwarding sub-layer may provide the function and technology such as multiple queuing and traffic treatment for DetNet application flows. The DetNet data plane may also encode the queuing related information in packets. The encapsulation of a DetNet flow allows the packets to be sent over an unique queuing technology. The DetNet forwarding nodes along the path can follow the queue scheduling carried in the packet to achieve the end-to-end bounded latency. The DetNet forwarding sub-layer may provide capabilities applying existing queuing mechanisms or traffic treatment. For example, the traffic treatment has been proposed in to decrease the micro-bursts in layer3 network for low-latency traffic. The time-scheduling queuing mechanisms includes the Time Aware Shaping [IIEEE802.1Qbv] and priority-scheduling includes the Credit-Based Shaper [IEEE802.1Q-2014] with Asynchronous Traffic Shaping[IEEE802.1Qcr]. The cyclic-scheduling queuing mechanism has been proposed in [IEEE802.1Qch] and improved in . The deadline-scheduling queuing mechanism has been proposed in and improved in . The per-flow queuing mechanism includes Guaranteed-Service Integrated service (IntServ) . The timeslot-based queuing mechanism has been proposed in .

1. deterministic latency information DetNet forwarding sub-layer may provide the function and technology such as multiple queuing and traffic treatment for DetNet application flows to guarantee the deterministic latency. The DetNet data plane may also encode the deterministic latency related information in packets. The information ensuring deterministic latency should be provided for EDP. A common and simplified data fields can be defined as per including encapsulation in IPv6 , MPLS and . For example, the encapsulation of a DetNet flow allows the packets to be sent over an unique queuing mechanism. It is required to carry queuing related information in data plane so as to make appropriate packet forwarding and scheduling decisions to meet the time bounds.

An IP data plane may operate natively or through the use of an encapsulation. IP encapsulation can satisfy enhanced DetNet requirements. Explicit inclusion of the flow identification, path selection, queuing and traffic treatment is possible through the use of IP options, IP extension headers or existing IP headers. For example, the queuing information has been carried in IPv6/SRv6 networks as defined in and . MPLS provides a service sub-layer for traffic by adding specific flow attributes (S-label and d-cw) in packets. MPLS provides a forwarding sub-layer for traffic over implicit and explicit paths such as F-Labels. Explicit inclusion of queuing and traffic treatment is possible through the use of MPLS metadata or MPLS TC field as defined in and .

As described in section 3.6.1, 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 data 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 the queuing parameters are carried in deterministic latency information may be selected in path computation as per .

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.

TBA

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