| Internet-Draft | EDP Framework for Scaling Deterministic | July 2023 |
| Xiong, et al. | Expires 11 January 2024 | [Page] |
The Enhanced Deterministic Networking (EDN) is required to provide the enhancement of flow identification and packet treatment for Deterministic Networking (DetNet) to achieve the DetNet QoS in scaling networks.¶
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.¶
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According to [RFC8655], 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 [RFC8938]. The IP and MPLS DetNet data plane has been defined respectively in [RFC8939] and [RFC8964]. 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 QoS in large-scale networks. The Enhanced DetNet Data Plane (EDP) is required to support a data plane method of flow identification and packet treatment. [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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 [RFC8938]. [I-D.ietf-detnet-scaling-requirements] 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 [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. 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 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Abbreviations and definitions used in this document:¶
As defined in [RFC8938], 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.¶
+----------------------------------+
|Service sub-layer: |
| |
| Traffic Scheduling |
+----------------------------------+
|Forwarding sub-layer: |
| |
| Deterministic Routes |
| Time-based Resources Allocation |
| Queuing Mechanisms |
+----------------------------------+
From the perspective of differentiated services requirements in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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. So the Differentiated DetNet QoS (DD-QoS) is proposed as per [I-D.xiong-detnet-teas-te-extensions]. The DetNet data plane should support the service-level identification of multiple flows to achieve the differentiated deterministic QoS for each DetNet flow. It may also downscale the network operations with a large number of deterministic flows and network nodes in scaling networks.¶
DetNet service sub-layer may provide the traffic scheduling function in enhanced DetNet data plane to support the service-level identification of multiple flows to achieve the differentiated deterministic QoS.¶
As discussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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. The deterministic routes 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. Moreover, the enhanced DetNet data plane should perform the deterministic routes and forwarding at different traffic classes.¶
DetNet forwarding sub-layer may provide the deterministic routes function in enhanced DetNet data plane for the deterministic routing and forwarding of traffic from ingress nodes to egress nodes.¶
As discussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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. The deterministic links should be used to provide a one-dimensional deterministic metric to guarantee for the deterministic forwarding capabilities at different levels as defined in [I-D.xiong-detnet-teas-te-extensions]. The deterministic links are provided and distributed to support the deterministic resource and forwarding capabilities indicated by Deterministic Class-Type (DT).¶
The computing end-to-end delay bounds is defined in [RFC9320]. 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 [I-D.peng-lsr-flex-algo-deterministic-routing].¶
When DetNet services with different SLA requirements requested to transmit, one or more deterministic paths may be established based on the deterministic links. In the distributed scenario, deterministic loose routes are computed on the device through routing protocols. Interior Gateway Protocol (IGP) [I-D.peng-lsr-flex-algo-deterministic-routing] is used to compute deterministic routes based on deterministic-delay inside a domain, and Border Gateway Protocol (BGP) [I-D.peng-idr-bgp-metric-credit] is used to compute deterministic routes based on accurate delay/jitter across domains.¶
As discussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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. As per [I-D.bernardos-detnet-multidomain], technical gaps are existing in multi-domain DetNet scenarios. 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.¶
As discussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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 discussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] section 3.3.2, the allocation of queuing related resources or time-based resources should be taken into consideration in enhanced DetNet data plane. The DetNet networks need to shield the differences between network capabilities. Deterministic resource is the basis for providing deterministic services. It refers to the time-based 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. As per [I-D.xiong-detnet-teas-te-extensions], Time-based Resources Container (TRC) is defined to provide the time-based resources with different traffic classes. The container contains the corresponding scheduling resources reserved in control plane to guarantee the capability and then the time-based resources should be allocated in enhanced DetNet data plane.¶
DetNet forwarding sub-layer may provide the time-based resources allocation function in enhanced DetNet data plane for the allocation of specific nodes and deterministic link time-based resources to specific flows and traffic classes. It also provide the admission control of a flow to a particular class of allocated resources.¶
As dicussed in [I-D.xiong-detnet-enhanced-detnet-gap-analysis] 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 [I-D.du-detnet-layer3-low-latency] 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 [I-D.dang-queuing-with-multiple-cyclic-buffers]. The deadline-scheduling queuing mechanism has been proposed in [I-D.stein-srtsn] and improved in [I-D.peng-detnet-deadline-based-forwarding]. The per-flow queuing mechanism includes Guaranteed-Service Integrated service (IntServ) [RFC2212]. The timeslot-based queuing mechanism has been proposed in [I-D.peng-detnet-packet-timeslot-mechanism].¶
DetNet forwarding sub-layer may provide the queuing and scheduling mechanisms in enhanced DetNet data plane to achieve the end-to-end bounded latency and multiple mechanisms may be proposed to provide different levels of bounded latency guarantees.¶
1. deterministic latency information¶
DetNet forwarding sub-layer may provide the enhanced function and technology such as multiple queuing mechanisms and traffic treatment for DetNet application flows to guarantee the deterministic latency. The enhanced DetNet data plane may 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 [I-D.xiong-detnet-data-fields-edp] including encapsulation in IPv6 [I-D.xiong-detnet-6man-queuing-option] , MPLS [I-D.sx-detnet-mpls-queue] and SRv6 [I-D.xiong-detnet-spring-srh-extensions]. 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.¶
2. traffic class information¶
DetNet service sub-layer may provide the enhanced function and technology such as traffic scheduling for DetNet application flows to achieve the differentiated DetNet QoS. The enhanced DetNet data plane may also encode the traffic class information in packets.¶
The DetNet Traffic Class (DC) has been defined to indicate the DetNet traffic class as per [I-D.xiong-detnet-teas-te-extensions]. The traffic class information can also reuse the IP DSCP or MPLS TC field.¶
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 [I-D.xiong-detnet-6man-queuing-option] and [I-D.xiong-detnet-spring-srh-extensions].¶
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 [I-D.sx-detnet-mpls-queue] and [I-D.eckert-detnet-mpls-tc-tcqf].¶
TBA¶
The authors would like to thank Peng Liu, Bin Tan, Aihua Liu Shaofu Peng for their review, suggestions and comments to this document.¶