| Internet-Draft | MNA for Deterministic Latency | May 2024 |
| Song, et al. | Expires 30 November 2024 | [Page] |
This document specifies formats and principles for the MPLS Network Action for Deterministic Latency to provide guaranteed latency services. They are used to make scheduling decisions for time-sensitive services running on Deterministic Network (DetNet) nodes that operate within a single or multiple domains.¶
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[RFC8655] defines Deterministic Network (DetNet) architecture. The overall framework for DetNet data plane is introduced in [RFC8938]. Deterministic Networking (DetNet) operates at the IP layer and delivers services with low data loss rates and bounded latency guarantee within a network domain.¶
[RFC8964] introduces the DetNet MPLS data plane technology providing a foundation of building blocks to enable PREOF (Packet Replication, Elimination and Ordering Functions (PREOF)) functions to DetNet service sub-layer and forwarding sub-layer. The DetNet service sub-layer includes a DetNet Control Word (d-CW), service label (S-Label), an aggregation label (A-Label) in special case of S-Label used for aggregation. The DetNet forwarding sub-layer supports one or more forwarding labels (F-Labels) used to forward a DetNet flow over MPLS domains. The DetNet forwarding sub-layer provides corresponding forwarding assurance with resource allocations and explicit routes.¶
To support time-sensitive service with ultra-low loss rates and deterministic latency, it is required to apply feasible scheduling mechanisms to specific applications for deterministic networking. As described in [RFC9320], the end-to-end bounded latency is considered as the sum of non-queuing and queuing delay bounds along with the queuing mechanisms.¶
The queuing mechanisms, as mentioned in [RFC9320] and [RFC8655], which include Time Aware Shaping IEEE802.1Qbv, Asynchronous Traffic Shaping IEEE802.1Qcr, cyclic-scheduling queuing mechanism proposed in IEEE802.1Qch. In terms of delay guarantee for different applications, to select the right scheduling/queuing mechanism applied to a specific application is required. Based on the existing DetNet MPLS encapsulations and mechanisms [RFC8964], the document defines the encoding format for Deterministic Latency Network Action (DLNA) option in MPLS data plane.¶
But with DetNet network scaling up or flows number increased in the same work, some enhanced data plane requirements for DetNet network are brought, which are described at the [I-D.ietf-detnet-scaling-requirements]. This document follows the enhanced data plane requirements and introduces the MPLS MNA solution to address the requirements specified at section 4.2 of [I-D.ietf-detnet-scaling-requirements]. The deterministic network should support synchronized or asynchronized queuing mechanisms. Different queuing mechanisms require different information to be defined as the DetNet-specific metadata to help the functions of ensuring deterministic latency, including regulation, queue management, etc.¶
The use case Delay Budgets for Time Bound Applications is under discussion at MPLS MNA [I-D.ietf-mpls-mna-usecases]. MPLS Network Actions (MNA) are used to indicate actions for LSPs and/or MPLS packets and to transfer data needed for these actions. [I-D.ietf-mpls-mna-hdr] defines the MNA solution for carrying Network Actions with Sub-Stack Data and associated Ancillary Data (AD) (i.e., in the MPLS label stack).¶
This document presents one MPLS MNA solution for Deterministic Latency. It follows the MPLS MNA requirements specified at [I-D.ietf-mpls-mna-requirements] and MPLS MNA header specifid at [I-D.ietf-mpls-mna-hdr] to support basic DetNet service and DetNet service with enhanced DetNet data plane requirements specified at [I-D.ietf-detnet-scaling-requirements] .¶
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.¶
Refer to [RFC8655], [RFC8964], [I-D.ietf-mpls-mna-hdr] and [RFC9320] for the key terms used in this document.¶
Deterministic Latency (DL): The bound of network latency and delay variation between two DetNet endpoints.¶
Deterministic Latency Network Action (DLNA): Used to indicate deterministic latency network action for MPLS data plane.¶
[RFC8655] provides the architecture for deterministic networking (DetNet) which enables the service delivery of DetNet flows with extremely low packet loss rates and deterministic latency. The forwarding sub-layer provides corresponding forwarding assurance but can not provide the deterministic latency (including bounded latency, low packet loss and in-order delivery). As described at [RFC9320], the end-to-end bounded latency for one DetNet flow is the sum of delay bound of non-queuing and queuing processing latency. The delay bound for non-queuing processing may include output delay, link delay, frame preemption delay, and processing delay, the delay bound for queuing processing may include regulator delay, queuing delay. It is assumed that the delay of non-queuing processing is fixed or be ignorable, the delay of queuing processing is variable. To realize the guarantee of bounded latency service it is important to select right queuing methodology applied to specific applications and carry necessary queuing delay information for computation of end-to-end latency.¶
The existing switches and routers have the ability to classify traffic and provide independent queuing mechanisms based on Class of Service (CoS) that CoS is used in the Priority Code Point (PCP) field of the 802.1Q, DSCP field in IPv4 header and Traffic Class field in IPv6 field. CoS defines the priority levels of traffic and QoS uses these CoS values to handle traffic to optimize traffic transmission. To achieve deterministic/bounded latency service requirements, the queuing mechanisms, as mentioned in [RFC9320] and [RFC8655], Time Aware Shaping IEEE802.1Qbv, Asynchronous Traffic Shaping IEEE802.1Qcr, cyclic-scheduling queuing mechanism proposed in IEEE802.1Qc are used in single or multiple domains network.¶
The DetNet data plane encapsulation in transport network with MPLS data plane is specified in [RFC8964]. There is a requirement to provide deterministic latency option to address DetNet scaling question and support the enhanced data plane requirements described at [I-D.ietf-detnet-scaling-requirements]. The option should include end-to-end and hop-by-hop processing of packets to be adaptive to different queuing mechanisms in DetNet networks.¶
The DetNet routers in data plane perform MPLS forwarding functions using a feasible way with sufficient network resources for the incoming packets, and makes right selection on the queuing or scheduling mechanisms applied for specific DetNet flows to satisfy strict deterministic service criteria in the forwarding output port. The information for the queuing or scheduling mechanisms are carried in the MPLS header. Refer to [I-D.stein-srtsn], considering the time latency information are processed per hop so the time latency informations (such as deadline time, cycle identify, etc.) of each DetNet node for DetNet flows are expected to be carried as a set of lists of LSEs in MPLS data plane.¶
This document provides an optional MNA header to address enhanced DetNet data plane requirements described at [I-D.ietf-detnet-scaling-requirements] to support different deterministic service categories such as bandwidth guarantee, bounded latency, loss ratio guarantee, etc.¶
To support deterministic/bounded latency service this document introduces an MPLS MNA MPLS Network Action (MNA) option for Deterministic Latency Network Action (DLNA). As shown in Figure 1, the MNA label is inserted to indicate the presence of MPLS Network Actions. The format for DLNA follows the DetNet data plane MPLS encapsulation specified at [RFC8964] and MNA encapsulation specified in [I-D.ietf-mpls-mna-hdr] and [I-D.ietf-mpls-mna-fwk], which is comprised of a set of Label Stack Entries (LSEs) that carry the DLNA Indicator and Ancillary Data to perform DLNA actions for MPLS packets.¶
+---------------------------+ | DetNet App-Flow | | Payload Packet | +---------------------------+--\ | DetNet Control Word | | +---------------------------+ | | S-Label | | DetNet +---------------------------+ | Data Plane | DLNA | | MPLS Encapsulation +---------------------------+ | | MNA Label | | +---------------------------+ | | F-Label(s) | / +---------------------------+--/ | Data-Link | +---------------------------+ | Physical | +---------------------------+
As defined in [RFC8964], the DetNet functionality PREOF (Packet Replication, Elimination and Ordering Functions) is supported through d-CW,S-label and F-label. The queue mechanism for DetNet networks is expected to use the existing COS mechanism, such as PCP for VLAN, DSCP for IPv4, Traffic Class for IPv6. The S-lable is at the bottom of MPLS label stack and normally followed by d-CW (DetNet Control-Word, i.e., sequence number). The S-label is used to identify DetNet service-type. F-lable(s) identify explicit route and allocated resources for DetNet nodes, the route schedule and resource reservation are achieved via provision by controller. D-CW (i.e., sequence number) is used for ordering function of DetNet packets. To support backward compatibility, the aspects (DetNet d-CW, S-label, F-label and A-label) are kept shown in MPLS sub-stack but outside of MPLS MNA sub-stack. The base DetNet data plane MPLS encapsulation follows specification at [RFC8964]. For base DetNet services, it's assumed that the requirements can be satisfied via deploying CoS mechanisms (i.e., PCP for VLAN, DSCP for IPv4 and Traffic Class for IPv6) to DetNet network nodes.¶
For enhanced DetNet services, it is expected to deploy enhanced queueing mechanisms and the queueing information may be carried in data packets. The enhanced DetNet data plane requirements are specified in [I-D.ietf-detnet-scaling-requirements]. To support enhanced deterministic services, strict queuing technologies may be required for DetNet devices. Its related latency requirements may involve different categories: (1) Industrial, tight jitter, strict latency limit; (2) Industrial, strict latency limit; (3) Non-periodic, relative loose latency requirements; (4) Best effort. And different network implementations require different SLA requirements with different queueing mechanisms implemented in single or multiple network domains.¶
The Deterministic Latency Network Action Sub-Stack format for MNA is shown in Figure 2. The network action follows LSE format C to carry DLNA Opcode and LSE format D for Additional Data as specified in [I-D.ietf-mpls-mna-hdr].¶
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | |R|IHS|S| Res |U| NASL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DLNA Opcode | Reserved |DLNA Flag|S| Res | NAL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Deterministic Latency Data |S| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Deterministic Latency Data |S| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
As specified at [I-D.ietf-mpls-mna-hdr], The header for MPLS Sub-Stack Network Action encodes:¶
R (1 bit) : Reserved bit. This MUST be transmitted as zero and ignored upon receipt.¶
IHS (2 bits) : The processing scope of the sub-stack.¶
S (1 bit) : The Bottom of Stack [RFC3032].¶
Res (3 bits) : Reserved bits. These MUST be transmitted as zeros and ignored upon receipt.¶
U (1 bit): Unknown Action Handling.¶
NASL (4 bits) : The Network Action Sub-Stack Length (NASL). The number of additional LSEs in the sub-stack, not including the leading Format A LSE and the Format B LSE.¶
DLNA Opcode (7 bits): This is the first 7-bit value in the Label Field. The value is used to indicate DLNA network action with Data and to be assigned by IANA as value TBA1.¶
DLNA Flags (5 bits): A bit map that specifies the type of enhanced Deterministic latency. The supported Deterministic latency type is listed in Table 1.¶
| Bit | Deterministic Latency Type |
|---|---|
| 0 | Reserved |
| 1 | Latency Bound |
| 2 | Queuing Delay Bound |
Deterministic Latency Data (60 bits): The ancillary data LSEs for the Deterministic Latency Type.¶
The Deterministic Latency Data speicification refers to [RFC9320] and [I-D.ietf-detnet-dataplane-taxonomy], which introduces DetNet Bounded Latency Model. To support deterministic latency services the latency variation across the DetNet-aware or DetNet-unaware islands should be bounded and computable. The Deterministic Latency Bound of End-to-End and each nodes along with the DetNet flows should be included. The additional parameters specification is for further study and follow the latest discussion at DetNet working group.¶
This document requests one new IANA-managed code-point for Deterministic Latency processing. IANA maintains the "Network Action Opcodes" registry when created from IANA request in [I-D.ietf-mpls-mna-hdr]. IANA is requested to allocate a value for MPLS Network Action Opcode for Deterministic Latency Network Action from this registry:¶
| Value | Description | Reference |
|---|---|---|
| TBA1 | DLNA Opcode | This document |
Security considerations for DetNet are covered in the DetNet Architecture RFC8655 and DetNet Security Considerations [RFC9055]. MPLS security considerations are covered in [RFC8964], [RFC3031], [RFC3032]. These security considerations also apply to this document. The MNA security considerations speicified at [I-D.ietf-mpls-mna-hdr] and [I-D.ietf-mpls-mna-hdr] are also applicable to the procedures defined in this document.¶
The authors would like to acknowledge Shaofu Peng for his thorough review and very helpful comments.¶