| Internet-Draft | Differentiated DetNet QoS for Determinis | October 2023 |
| Xiong, et al. | Expires 25 April 2024 | [Page] |
This document describes the service requirements of scaling deterministic networks and proposes Differentiated DetNet QoS (DD-QoS) for deterministic services in enhanced DetNet.¶
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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 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). Three techniques are used by DetNet to provide these qualities of service including service protection, explicit routes and resource allocation.¶
[I-D.ietf-detnet-scaling-requirements] has mentioned the enhanced DetNet should support different levels of application requirements which is important for the DetNet deployment. [I-D.zhao-detnet-enhanced-use-cases] has described enhanced use cases and network requirements for scaling deterministic networks and seven levels of typical applications have been defined. Different levels of applications differ in the network ranges and SLAs requirements. Moreover, multiple services and traffic flows with different bounded latency requirements may be also co-existed in the same application. Multiple deterministic services may demand different set of SLAs and it may define more than one DetNet QoS levels according to different application scenarios. These flows should be transmitted and forwarded with different DetNet QoS behaviors. From the use cases in [RFC8578], DetNet applications differ in their network topologies and specific desired behavior and different services requires differentiated DetNet QoS.¶
This document describes the service requirements of scaling deterministic networks and proposes Differentiated DetNet QoS (DD-QoS) for deterministic services in enhanced DetNet.¶
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 [RFC2119].¶
The terminology is defined as [RFC8655].¶
DD-QoS: Differentiated DetNet QoS¶
DC: DetNet Traffic Class¶
5G network is oriented to the internet of everything. It need to supports the Ultra-reliable Low Latency Communications (uRLLC) services. The uRLLC services demand SLA guarantees such as low latency and high reliability and other deterministic and precise properties especially in Wide Area Network (WAN) applications.The uRLLC services should be provided in large-scale networks which cover the industries such as intelligent electrical network, intelligent factory, internet of vehicles, industry automation and other industrial internet scenarios. The industrial internet is the key infrastructure that coordinate various units of work over various system components, e.g. people, machines and things in the industrial environment including big data, cloud computing, Internet of Things (IOT), Augment Reality (AR), industrial robots, Artificial Intelligence (AI) and other basic technologies. For the intelligent electrical network, there are deterministic requirements for communication delay, jitter and packet loss rate. For example, in the electrical current difference model, a delay of 3~10ms and a jitter variation is no more than 100us are required. For the automation control, it is one of the basic application and the the core is closed-loop control system. The control process cycle is as low as millisecond level, so the system communication delay needs to reach millisecond level or even lower to ensure the realization of precise control. There are three levels of real-time requirements for industrial interconnection: factory level is about 1s, and process level is 10~100ms, and the highest real-time requirement is motion control, which requires less than 1ms. So the deterministic latency requirements are different with varying services and network scenarios.¶
As per [I-D.ietf-detnet-scaling-requirements], the enhanced DetNet should support different levels of application requirements. As defined in [RFC8655], the DetNet QoS can be expressed in terms of : Minimum and maximum end-to-end latency, bounded jitter (packet delay variation), packet loss ratio and an upper bound on out-of-order packet delivery. As described in [RFC8578], DetNet applications differ in their network topologies and specific desired behavior and different services requires differentiated DetNet QoS. In large-scale networks, multiple services with differentiated DetNet QoS can be co-existed in the same DetNet network. The classification of the deterministic flows within different levels should be taken into considerations. It is required to provide Latency, bounded jitter and packet loss dynamically and flexibly in all scenarios for each characterized flow.¶
As the Figure 1 shows, the services can be divided into 5 levels and level 2~5 is the DetNet flows and level-1 is non-DetNet flow. DetNet applications and DetNet QoS is differentiated within each level.¶
+--------------+---------+-----------+-----------+----------+------------+ | Item | Level-1 | Level-2 | Level-3 | Level-4 | Level-5 | +--------------+---------+-----------+-----------+----------+------------+ |Applications |Email | Voice | Audio and | AR/VR | Industrial | |Examples | | | Video | | | +--------------+---------+-----------+-----------+----------+------------+ |Differentiated|N/A |delay<300ms|delay<50ms |delay<20ms|delay<10ms | |SLAs | |jitter<50ms|jitter<50ms|jitter<5ms|jitter<100us| +--------------+---------+-----------+-----------+----------+------------+ |DetNet QoS |Bandwidth|Jitter | Delay | Low | Ultra-low | |Forwarding |Guarantee|Guarantee | Guarantee | delay | delay and | |Behaviors | | | |and jitter| jitter | +--------------+---------+-----------+-----------+----------+------------+
From the perspective of deterministic service requirements, deterministic QoS in the network can be divided into five types or levels:¶
Level-1: bandwidth guarantee. The indicator requirements include basic bandwidth guarantee and certain packet loss tolerance. There is no requirement for the upper bound of the latency, and no requirement for the jitter. Typical services include download and FTP services.¶
Level-2: jitter guarantee. The indicator requirements include: jitter<50ms, delay<300ms. Typical services include synchronous voice services, such as voice call.¶
Level-3: delay guarantee. The indicator requirements include: delay<50ms, jitter<50ms. Typical services include real-time communication services, such as video, production monitoring, and communication services.¶
Level-4: low delay and jitter guarantee. The indicator requirements include: delay<20ms, jitter<5ms. Typical services include video interaction services, such as AR/VR, holographic communication, cloud video and cloud games.¶
Level-5: ultra-low delay and jitter guarantee. The indicator requirements include: delay<10ms, jitter<100us. Typical services include production control services, such as power protection and remote control.¶
Moreover, different DetNet services is required to tolerate different percentage of packet loss ratio such as 99.9%, 99.99%, 99.999%, and so on.¶
Traditional Ethernet, IP and MPLS networks which is based on statistical multiplexing provides best-effort packet service and offers no delivery and SLA guarantee. As described in [RFC8655], the primary technique by which DetNet achieves its QoS is to allocate sufficient resources. But it can not be achieved by not sufficient resource which can be allocated due to practical and cost reason. So it is required to achieve the high-efficiency of resources utilization when provide the DetNet services.¶
As per [RFC8655], an important goal of the DetNet QoS is the bounded latency including the minimum and maximum end-to-end latency from source to destination, and bounded jitter. From the services requirements, a scaling network in enhanced DetNet needs to provide the deterministic services for various applications. The deterministic services may demand differentiated SLAs and different bounded latency guarantees. So multiple DetNet QoS levels should be supported according to different application scenarios.¶
Moreover, as per [RFC8938], the aggregation of individual flows may be still challenging for network operations with a large number of deterministic flows and network nodes in large-scale networks. It may provide traffic class scheduling than the flow scheduling. As per [I-D.xiong-detnet-large-scale-enhancements], the enhanced DetNet data plane should support the traffic scheduling based on traffic class and consider the differentiated DetNet QoS for each DetNet flow.¶
The differentiated QoS MAY be classified based on the applications in scaling networks. This document proposed the DetNet Traffic Class (DC) to indicate the traffic classes of Differentiated DetNet QoS (DD-QoS). The DetNet traffic class may be divided into 4 types:¶
+--------------+-----------+----------+----------+-----------+-----------+ |Differentiated| Bandwidth | Jitter | Delay | Low | Ultra-low | |DetNet QoS | Guarantee | Guarantee| Guarantee| delay and | delay and| |Forwarding | | | | and jitter| jitter | |Behaviors | | | | | | +--------------+-----------+----------+----------+-----------+-----------+ | DetNet | | | | | | | Traffic |Best-effort| DC-1 | DC-2 | DC-3 | DC-4 | | Class | | | | | | +--------------+-----------+----------+----------+-----------+-----------+
Different QoS class indicates different levels of applications with SLAs requirements and each class demands differentiated QoS behaviors as well as different DetNet capabilities in scaling network. For example, the behaviors of jitter guarantee and delay guarantee may implement different queuing mechanisms. Each QoS class can be divided into serveral sub-classes based on the SLAs requirements of the applications.¶
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