DetNet Working Group J. Joung Internet-Draft Sangmyung University Intended status: Informational J. Ryoo Expires: December 28, 2022 T. Cheung ETRI Y. Li Huawei P. Liu China Mobile June 26, 2022 Asynchronous Deterministic Networking Framework for Large-Scale Networks draft-joung-detnet-asynch-detnet-framework-00 Abstract This document describes an overall framework of Asynchronous Deterministic Networking (ADN) for large-scale networks. It specifies the functional architecture and requirements for providing latency and jitter bounds to high priority traffic, without time- synchronization of network nodes. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 28, 2022. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of Joung, et al. Expires December 28, 2022 [Page 1] Internet-Draft Asynchronous DetNet Framework June 2022 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Terms Used in This Document . . . . . . . . . . . . . . . 4 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 3. Conventions Used in This Document . . . . . . . . . . . . . . 4 4. Framework for Latency Guarantee . . . . . . . . . . . . . . . 4 4.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 4 4.2. Asynchronous Traffic Shaping (ATS) . . . . . . . . . . . 6 4.3. Flow Aggregate Interleaved Regulators (FAIR) . . . . . . 6 4.3.1. Overview of the FAIR . . . . . . . . . . . . . . . . 6 4.3.2. The performance of the FAIR . . . . . . . . . . . . . 7 4.4. Port-based Flow Aggregate Regulators (PFAR) . . . . . . . 7 5. Framework for Jitter Guarantee . . . . . . . . . . . . . . . 9 5.1. Problem statement . . . . . . . . . . . . . . . . . . . . 9 5.2. Buffered network (BN) . . . . . . . . . . . . . . . . . . 10 5.3. Properties of the BN . . . . . . . . . . . . . . . . . . 11 5.4. Frequency synchronization between the source and the buffer . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.5. Omission of the timestamper . . . . . . . . . . . . . . . 13 5.6. Mitigation of the increased E2E buffered latency . . . . 13 5.7. Multi-sources single-destination flows' jitter control . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 9. Contributor . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction Deterministic Networking (DetNet) provides a capability to carry specified unicast or multicast data flows for real-time applications with extremely low data loss rates and bounded latency within a network domain. The architecture of DetNet is defined in RFC 8655 [RFC8655], and the overall framework for DetNet data plane is provided in RFC 8938 [RFC8938]. Various documents on DetNet IP (Internet Protocol) and MPLS (Multi-Protocol Label Switching) data Joung, et al. Expires December 28, 2022 [Page 2] Internet-Draft Asynchronous DetNet Framework June 2022 planes and their interworking with Time-Sensitive Networking (TSN) have been standardized. Technical elements necessary to extend DetNet to a large-scale network spanning multiple domains are identified in [I-D.liu-detnet-large-scale-requirements]. This document considers the problem of guaranteeing both latency upper bounds and jitter upper bounds in a large-scale networks with any type of topology, with random dynamic input traffic. The jitter is defined as the latency difference between two packets within a flow, not a difference from a clock signal or from an average latency, as is summarized in RFC 3393 [RFC3393]. In large-scale networks, the end-nodes join and leave, and a large number of flows are dynamically generated and terminated. Achieving satisfactory deterministic performance in such environments would be challenging. The current Internet, which has adopted the DiffServ architecture, has the problem of the burst accumulation and the cyclic dependency, which is mainly due to FIFO queuing and strict priority scheduling. Cyclic dependency is defined as a situation wherein the graph of interference between flow paths has cycles [THOMAS]. The existence of such cyclic dependencies makes the proof of determinism a much more challenging issue and can lead to system instability, that is, unbounded delays [ANDREWS][BOUILLARD]. The Internet architecture does not have an explicit solution for the jitter bound as well. Therefore, solving the problem of latency and jitter as a joint optimization problem would be even more difficult. The basic philosophy behind the framework proposed in this document is to minimize the latency bounds first by taking advantage of the work conserving schedulers with regulators, and then minimize the jitter bounds by adjusting the packet inter-departure times to reproduce the inter-arrival times, at the boundary of a network. We argue that this is simpler than trying to minimize the latency and the jitter at the same time. The direct benefit of such simplicity is its scalability. For the first problem of guaranteeing latency bound alone, the IEEE asynchronous traffic shaping (ATS) [IEEE802.1Qcr], the flow-aggregate interleaved regulators (FAIR) [FAIR][Y.3113] frameworks, and the port-based flow aggregate regulators (PFAR) [ADN] are proposed as solutions. The key component of the ATS and the FAIR frameworks is the interleaved regulator (IR). The IR has a single queue for all flows of the same class from the same input port. The head of the queue (HOQ) is examined if the packet is eligible to exit the regulator. To decide whether it is eligible, the IR must maintain the individual flow states. The key component of the PFAR framework is the regulators for flow aggregates (FA) per port per class, which Joung, et al. Expires December 28, 2022 [Page 3] Internet-Draft Asynchronous DetNet Framework June 2022 regulates the FA based on the sum of average rates and the sum of maximum bursts of the flows that belong to the FA. For the second problem of guaranteeing jitter bound, it is necessary to assume that the first problem is solved, that is, the network guarantees latency bounds. Furthermore, the network is required to specify the value of the latency bound for a flow. The end systems at the network boundary, or at the source and destination nodes, then can adjust the inter-departure times of packets, such that they are similar to their inter-arrival times. In order to identify the inter-arrival times at the destination node, or at the network edge near the destination, the packets are required to specify their arrival times, according to the clock at the source, or the network edge near the source. The clocks are not required to be time- synchronized with any other clocks in a network. In order to avoid a possible error due to a clock drift between a source and a destination, they are recommended to be frequency-synchronized. 2. Terminology 2.1. Terms Used in This Document 2.2. Abbreviations 3. Conventions Used in This Document 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. 4. Framework for Latency Guarantee 4.1. Problem Statement In Section 4, we consider there are only two classes of traffic. The high priority traffic requires latency upper bound guarantee. All the other traffic is considered to be the low priority traffic, and be completely preempted by the high priority traffic. High priority (HP) traffic is our only focus. It is well understood that the necessary conditions for a flow to have a bounded latency inside a network, are that; o a flow entering a network conforms to a prescribed traffic specification (TSpec), including the arrival rate and the maximum burst size, and Joung, et al. Expires December 28, 2022 [Page 4] Internet-Draft Asynchronous DetNet Framework June 2022 o all the network nodes serve the flow with a service rate which are greater than or equal to the arrival rate. These conditions make the resource reservation and the admission control mandatory. These two functions are considered given and out of scope of this document. Here, the notion of arrival and service rates represent sustainable or average values. A short-term discrepancy between these two rates contributes to the burst size increment, and therefore accumulation over the flow's path, which again contributes to the latency bound increment. Therefore, the value of accumulated burst size is a critical performance metric. The queuing and scheduling of a flow plays a key role in deciding the accumulated burst size. Ideally, the flows can be queued in separate queues and the queues are scheduled according to the flow rates. In this case a flow can be considered protected. With practical fair schedulers, such as the Deficit Round Robin (DRR), a protected flow still can be affected by the other flows as much as their maximum packet lengths. If we adopt a separate queue per flow at an output port, and assume identical flows from all the input ports, then the maximum burst size of a flow out of the port, Bout, is given as the following: Bout < Bin + (n-1)L*r/C, where Bout is the outgoing flow's maximum burst size, Bin is the incoming flow's maximum burst size, n is the number of the flows, L is the maximum packet size, r is the average rate of the flow, and C is the link capacity. This approach was taken in the integrated services (IntServ) framework [RFC2212]. The separate queues in the aforementioned case can be too many to be handled in real time, especially at the core of large-scale networks. The common practice therefore is to put all the HP flows in a single queue, and serve them with higher priority than best effort traffic. It is also well known that a proper scheduling scheme, such as the strict priority (SP) scheduling can guarantee service rates larger than the arrival rates, therefore the latency can still be guaranteed. With such a single aggregate queue the flows are not considered protected, however. In this case a flow's burst size in a node can be increased proportionally to the sum of maximum burst sizes of the other flows in the queue. That is, Bout < Bin + (n-1)Bin*r/C. Joung, et al. Expires December 28, 2022 [Page 5] Internet-Draft Asynchronous DetNet Framework June 2022 The second product term on the right-hand side represents the amount of increased maximum burst. It is dominated by the term (n-1)Bin, which is the maximum total burst from the other flows. Moreover, this increased burst affects the other flows' burst size at the next node, and this feedforward can continue indefinitely where a cycle is formed in a network. This phenomenon is called a cyclic dependency of a network. It is argued that the burst accumulation can explode into infinity, therefore the latency is no longer guaranteed. As such, a flow is required to be protected to a certain level, from the other flows' bursts, such that its burst accumulations are kept within a necessary value. By doing so, the other flows are also protected. The regulation, or shaping, is the proposed key component in this document for such protection. It is the direct solution to decrease the accumulated burst into a desirable level. However, if the regulation needs a separate queue per flow, then the scalability would be harmed just like the ideal IntServ case. In this document the IR or the regulations on flow aggregates are proposed. The key requirement for latency guarantee is therefore to have scalability and a certain level of flow protection. 4.2. Asynchronous Traffic Shaping (ATS) The first solution in this document for latency guarantee is the IEEE TSN TG's ATS technology. Essentially it is a combined effort of the flow aggregation per node per input/output ports pair per class, and the interleaved regulator per flow aggregate (FA). The IR examines the HOQ, identifies the flow the packet belongs to, and transfers the packet only when it is eligible according to the initial TSpec of the flow. This solution can have only one queue per FA, but suffers from having to maintain each individual flow state. The detailed description on ATS can be found in [IEEE802.1Qcr]. 4.3. Flow Aggregate Interleaved Regulators (FAIR) 4.3.1. Overview of the FAIR In the FAIR framework, the network can be divided into several aggregation domains (ADs). HP flows of the same path within an AD are aggregated into an FA. IRs per FA are implemented at the boundaries of the ADs. An AD can consist of arbitrary number of nodes. The FA can be further subdivided based on the flow requirements and characteristics. For example, only video flows of the same path are aggregated into a single FA. Joung, et al. Expires December 28, 2022 [Page 6] Internet-Draft Asynchronous DetNet Framework June 2022 Figure 1 shows an example architecture of the FAIR framework. The IRs at the AD boundaries suppress the burst accumulations across the ADs with the latency upper bounds intact as they do in IEEE TSN ATS, if the incoming flows are all properly regulated, and the AD guarantees the FIFO property to all the packets in the FA [LEBOUDEC]. It is sufficient to put every FA into a single FIFO queue in a node, in order to maintain the FIFO property within an AD. However, in this case, if cycles are formed, the burst accumulations inside an AD can be accumulated indefinitely. If the topology does not include a cycle and the latency bound requirement is not stringent, then the FIFO queue and the SP scheduler would be allowable. Otherwise, the FAs are recommended to be treated with separated queues and fair- queuing schedulers for flow protection. .~~. +---+ .~~, +---+ .~~. +---+ [ ] |IR | [ ] |IR | [ ] +----+ |Src|->[ AD ]->|per|->[ AD ]-> ...|per|... ->[ AD ]->|Dest| +---+ [ ] |FA | [ ] |FA | [ ] +----+ '~~' +---+ '~~' +---+ '~~' Figure 1: FAIR Framework 4.3.2. The performance of the FAIR The FAIR guarantees an end-to-end delay bound with reduced complexity compared to the traditional flow-based approach. Numerical analysis shows that, with a careful selection of AD size, the FAIR with DRR schedulers yields smaller latency bounds than both the IntServ and the ATS [FAIR]. The ATS can be considered as a special case of the FAIR with the FIFO schedulers, where all the ADs encompass only a single hop. The IntServ can also be considered as an extreme case of the FAIR with fair schedulers and queues per FA, with an AD corresponding to an entire network; therefore, regulators are unnecessary. 4.4. Port-based Flow Aggregate Regulators (PFAR) The IR in the ATS and the FAIR suffers from two major complex tasks; the flow state maintenance and the HOQ lookup to determine the flow to which the packet belongs. Both tasks involve real-time packet processing and queue management. As the number of flows increases, the IR operation may become burdensome as much as the per- flow regulators. Without maintaining individual flow states, however, the flows can be protected to a certain level, as is described in this section. Joung, et al. Expires December 28, 2022 [Page 7] Internet-Draft Asynchronous DetNet Framework June 2022 The ATS and FAIR mitigates the burst increment by placing IRs behind a FIFO system. For example, consider an ATS node with a single queue at an output port for HP traffic. The IR assigned for an input port forms a single queue for the flows from the same input port. Further consider the set of incoming flows from the same input port of the ATS node. Let us call this set of flows the incoming flow aggregate (FAin). If we assume identical FAins from all the input ports, then the maximum burst size of an arbitrary set of flows out of the port, Bout, is given as the following: Bout < Bin + (p-1)B*r/C, where Bin is the sum of maximum burst sizes of the flows within the FAin, B is the sum of initial maximum burst sizes of the flows within the FAin, and p is the number of the ports in the node. The port-based FA (PFA) is defined as a set of HP flows in the same class, which share the input and output ports in a relay node, such as a switch or router. The only aggregation criteria for a PFA are the ports and the class. The port-based flow aggregate regulators (PFAR) framework puts a regulator for each PFA in an output port module, just before the class-based queuing/scheduling system of the output port module. The PFAR framework sees a PFA as a single flow with the "PFA-Tspec", {the sum of the maximum initial bursts; and the sum of the initial arrival rates} of the flows that are the elements of the PFA; and regulates the PFA to meet its PFA-Tspec. The PFARs can be placed at the output port of a node before the output SP scheduler. The architecture is similar to that suggested in the IEEE ATS, except that in the ATS, the IRs are placed instead of the PFARs. The burst increment of an FA in the PFAR architecture is identical to that in the ATS, which is given as; Bout < Bin + (p-1)B*r/C, where B is again the initial maximum burst size of FAs. However, the regulators in PFAR does introduce additional latency, which is given as D < (Bin - B)/r, where D is the latency within the regulator. Note that Bout is a function of (n-1)B, not (n-1)Bin; in other words, the burst size out of a node is affected only by the initial burst sizes of the other FAs from different input ports of the node. This Joung, et al. Expires December 28, 2022 [Page 8] Internet-Draft Asynchronous DetNet Framework June 2022 property makes the D or Bout do not increase exponentially even in the existence of cyclic dependencies. With the PFAR, the HOQ flow identification process is unnecessary, and only the PFAs' states, instead of individual flows' states, must be maintained at a node. In this respect, the complexity of process of PFAR is reduced compared to IR of the ATS or the FAIR. In a recent study [ADN], it was also shown, through a numerical analysis with symmetrical networks with cycles, that PFAR, when implemented at every node, can achieve comparable latency bounds to the IEEE ATS technique. The ATS, the FAIR, and the PFAR frameworks maintain regulators per FA. The FAs in these frameworks are composed of the flows sharing the same ingress/egress ports of an AD. The ADs can encompass a single hop or multiple hops. The regulators can be the IR or the aggregate regulator. There can be other combinations of AD and regulator type, which could be further investigated and compared to the frameworks introduced in this document. 5. Framework for Jitter Guarantee 5.1. Problem statement The problem of guaranteeing jitter bounds in arbitrarily sized networks with any type of topology with random dynamic input traffic is considered. There are several possible solutions to guarantee jitter bounds in packet networks, such as IEEE TSN's cyclic queuing and forwarding (CQF) [IEEE802.1Qch], its asynchronous variations [I-D.yizhou-detnet-ipv6-options-for-cqf-variant], and the latency- based forwarding (LBF) [LBF]. The CQF requires time-synchronization across every node in the network including the source. It is not scalable to a large network with significant propagation delays between the nodes. The asynchronous CQFs are scalable, but they may not satisfy applications' jitter requirements. This is because their jitter bounds cannot be controlled as desired, but are only determined by the cycle time, which should be large enough to accommodate all the traffic to be forwarded. The systems with slotted operations such as the CQF and its variations turn the problem of packet scheduling into the problem of scheduling flows to fit into slots. The difficulty of such a slot Joung, et al. Expires December 28, 2022 [Page 9] Internet-Draft Asynchronous DetNet Framework June 2022 scheduling is a significant drawback in large scale dynamic networks with irregular traffic generations and various propagation delays. The LBF is a framework of the forwarding action decision based on the flow and packet status, such as the delay budget left for a packet in a node. The LBF does not specify the actions to take according to the status. It suggests a packet slow down or speedup by changing the service order, by pushing packets into any desirable position of a first out queue, as a possible action to take. In essence, by having latency budget information of every packet, the LBF is expected to maintain the latency and jitter within desired bounds. The processing latency required in LBF includes times 1) to lookup the latency budget information on every packet header, 2) to decide the queue position of the packet, 3) to modify the queue linked list, and 4) to update the budget information on the packet upon transmission. This processing latency, however, can affect the scalability especially in high speed core networks. The ATS, the FAIR, and the PFAR utilize the regulation function to proactively prevent the possible burst accumulation in the downstream nodes. It is not clear whether the LBF can take such preventive action. If so the LBF can also act as a regulator and yield a similar latency bound. 5.2. Buffered network (BN) The BN framework in this document for jitter bound guarantee is composed of o a network that guarantees latency upper bounds; o a timestamper for packets with a clock that is not necessarily synchronized with the other nodes, which resides in between, including the source and the network ingress interface; and o a buffer that can hold the packets for a predetermined interval, which resides in between, including the destination and the network egress interface. Figure 2 depicts the overall architecture of the BN framework for jitter-bound guarantees [BN]. Only a single flow is depicted between the source and destination in Figure 2. The arrival (an), departure (bn), and buffer-out (cn) instances of the nth packet of a flow are denoted. The end-to-end (E2E) latency and the E2E buffered latency are defined as (bn-an) and (cn-an), respectively. Joung, et al. Expires December 28, 2022 [Page 10] Internet-Draft Asynchronous DetNet Framework June 2022 +--------------+ +-----+an +-------------+ | Network with |bn +--------+cn +-------+ | Src |-->| Timestamper |-->| latency |-->| Buffer |-->| Dest. | +-----+ +-------------+ | guarantee | +--------+ +-------+ +--------------+ |<--------------- E2E latency ------>| |<--------------- E2E buffered latency ---------->| Figure 2: Buffered Network (BN) Framework for Jitter Guarantee The buffer supports as many as the number of the flows destined for the destination. In cases where the buffer is not suitable to be placed within an end station, the network can attach a buffering function at the boundary. The destination shown in Figure 2 can also be a small deterministic network. There is an entity for time- stamping the arrival instances to the packets. The time-stamping function can use the real-time transport protocol (RTP) over the user datagram protocol or the transmission control protocol (TCP). Either the source or network ingress interface can stamp the packet. In the case where the source stamps, the timestamp value is the packet departure instance from the source, which is only a propagation time away from the packet arrival instance to the network. The source and destination do not need to share a synchronized clock. All we need to know is the differences between the time stamps, that is, the information about the inter-arrival times. In the BN framework in Figure 2, it is recommended that the latency- lower bound information be provided by the network. The lower bound may be attributed to transmission and propagation delays within the network. The buffer holds packets in a flow according to the predefined intervals. The decision of the buffering intervals involves the timestamp within each packet. 5.3. Properties of the BN Let the arrival instance of the nth packet of a flow be an. Similarly, let bn be the departure time from the network of the nth packet. Then, a1 and b1 are the arrival and departure instances of the first packet of the flow, respectively. The first packet of a flow is defined as the first packet generated by the source, among all the packets that belong to the flow. Further, let cn be the buffer-out instance of the nth packet of the flow. Let us define m as the jitter control parameter, which will be described later in detail. Since buffers can be without cut-through capability, the processing delay within a buffer has to be taken in account. Let gn be the processing delay within the buffer of the nth packet of the flow. Joung, et al. Expires December 28, 2022 [Page 11] Internet-Draft Asynchronous DetNet Framework June 2022 The gn includes the time to look up the timestamp and to store/ forward the packet. It does not include an intentional buffer- holding interval. By definition, cn - bn >= gn. Let max_n(gn)=g, the maximum processing delay for the flow in the buffer. It is assumed that a buffer can identify the value of g. Let U and W be the latency upper and lower bounds guaranteed to the flow by the network. The rules for the buffer-holding interval decision are given as follows: o c1=(b1+m-W), o cn=max{(bn+g), (c1+an-a1)}, for n > 1. Furthermore, m is required to meet the inequality m >= W+g. The second rule governing the cn implies that a packet should be held in the buffer to make its inter-buffer-out time, (cn-c1), equal to the inter-arrival time, (an-a1). However, when its departure from the network is too late, the inter-buffer-out time should be larger than the inter-arrival time, then hold the packet as much as the maximum processing delay in the buffer, that is, cn=bn+g. The buffer does not need to know the exact values of an or a1. It is sufficient to determine the difference between these values, which can be easily obtained by subtracting the timestamp values of the two packets. The following theorems holds [ADN]. Theorem 1 (Upper bound of E2E buffered latency). The latency from the packet arrival to the buffer-out instances (cn-an), is upper bounded by (U-W+m). Theorem 2 (Lower bound of E2E buffered latency). The latency from the packet arrival to the buffer-out instances (cn-an), is lower bounded by m. Theorem 3 (Upper bound of jitter). The jitter is upper bounded by max{0, (U+g-m)}. By setting m=(U+g), we can achieve zero jitter. In this case, the E2E buffered latency bound becomes (2U+g-W), which is roughly twice the E2E latency bound. In contrast, if we set m to its minimum possible value W, then the jitter bound becomes (U+g-W), which is roughly equal to U, while the E2E buffered latency bound becomes U, which is the same as the E2E latency bound. Joung, et al. Expires December 28, 2022 [Page 12] Internet-Draft Asynchronous DetNet Framework June 2022 The parameter m directly controls the holding interval of the first packet. It plays a critical role in determining the jitter and the buffered latency upper bounds of a flow in the BN framework. The larger the m, the smaller the jitter bound, and the larger the latency bound. With a sufficiently large m, we can guarantee zero jitter, at the cost of an increased latency bound. 5.4. Frequency synchronization between the source and the buffer Clock drift refers to phenomena wherein a clock does not run at exactly the same rate as a reference clock. If we do not frequency- synchronize the clocks of different nodes in a network, clock drift is unavoidable. Consequently, jitter occurs owing to the clock frequency difference or clock drift between the source (timestamper) and the buffer. Therefore, it is recommended to frequency- synchronize the source (timestamper) and the buffer. 5.5. Omission of the timestamper For isochronous traffic whose inter-arrival times are well-known fixed values, and the network can preserve the FIFO property for such traffic, then the timestampers can be omitted. Otherwise the FIFO property cannot be guaranteed, then a sequence number field in the packet header would be enough to replace the timestamper. 5.6. Mitigation of the increased E2E buffered latency The increased E2E buffered latency bound by the proposed framework, from U to almost 2U, can be mitigated by one of the added functionalities given as follows. 1) First, one can measure the E2E latency of a flow's first packet exactly, and buffer it to make its E2E buffered latency be U. Then, by following the rules given in Section 5.3, every subsequent packet will experience the same E2E buffered latency, which is U, with zero jitter. An example of the exact latency measurement may be performed by time-synchronization between the source (timestamper) and the buffer. However, how to measure the latency is for further investigation. 2) Second, one can expedite the first packet's service with a special treatment, to make its latency lower, compared to the other packets of the flow. If we can make the first packet's latency to be a small value d, then every packet will experience the same buffered latency d+U, with zero jitter. Considering that the E2E latency bound is calculated from the worst case in which rare events occur Joung, et al. Expires December 28, 2022 [Page 13] Internet-Draft Asynchronous DetNet Framework June 2022 simultaneously, however, the first packet's latency is likely to be far less than what the bound suggests. Therefore, the special treatment to the first packet may be ineffective in real implementations. 5.7. Multi-sources single-destination flows' jitter control The BN framework can also be used for jitter control among multiple sources' flows having a single destination. When a session is composed of more than one sources, physically or virtually separated, the buffer at the boundary can mitigate the latency variations of packets from different sources due to different routes or network treatments. Such a scenario may arise in cases such as 1) that a central unit controls multiple devices for a coordinated execution in smart factories, or 2) multi-user conferencing applications, in which multiple devices/users physically separated can have a difficulty in real- time interactions. The sources, or the ingress boundary nodes of the network, need to be synchronized with each other in order for the time-stamps from separated sources to be able to identify the absolute arrival instances. 6. IANA Considerations There are no IANA actions required by this document. 7. Security Considerations This section will be described later. 8. Acknowledgements 9. Contributor 10. References 10.1. Normative References [I-D.liu-detnet-large-scale-requirements] Liu, P., Li, Y., Eckert, T., Xiong, Q., and J. Ryoo, "Requirements for Large-Scale Deterministic Networks", draft-liu-detnet-large-scale-requirements-02 (work in progress), April 2022. Joung, et al. Expires December 28, 2022 [Page 14] Internet-Draft Asynchronous DetNet Framework June 2022 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, "Deterministic Networking Architecture", RFC 8655, DOI 10.17487/RFC8655, October 2019, . [RFC8938] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S. Bryant, "Deterministic Networking (DetNet) Data Plane Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020, . 10.2. Informative References [ADN] Joung, J., Kwon, J., Ryoo, J., and T. Cheung, "Asynchronous Deterministic Network Based on the DiffServ Architecture", IEEE Access, vol. 10, pp. 15068-15083, doi:10.1109/ACCESS.2022.3146398, 2022. [ANDREWS] Andrews, M., "Instability of FIFO in the permanent sessions model at arbitrarily small network loads", ACM Trans. Algorithms, vol. 5, no. 3, pp. 1-29, doi: 10.1145/1541885.1541894, July 2009. [BN] Joung, J. and J. Kwon, "Zero jitter for deterministic networks without time-synchronization", IEEE Access, vol. 9, pp. 49398-49414, doi:10.1109/ACCESS.2021.3068515, 2021. [BOUILLARD] Bouillard, A., Boyer, M., and E. Le Corronc, "Deterministic network calculus: From theory to practical implementation", in Networks and Telecommunications. Hoboken, NJ, USA: Wiley, doi: 10.1002/9781119440284, 2018. [FAIR] Joung, J., "Framework for delay guarantee in multi-domain networks based on interleaved regulators", Electronics, vol. 9, no. 3, p. 436, doi:10.3390/electronics9030436, March 2020. Joung, et al. Expires December 28, 2022 [Page 15] Internet-Draft Asynchronous DetNet Framework June 2022 [I-D.yizhou-detnet-ipv6-options-for-cqf-variant] Li, Y., Ren, S., Li, G., Yang, F., Ryoo, J., and P. Liu, "IPv6 Options for Cyclic Queuing and Forwarding Variants", draft-yizhou-detnet-ipv6-options-for-cqf-variant-00 (work in progress), June 2022. [IEEE802.1Qch] IEEE, "IEEE Standard for Local and metropolitan area networks -- Bridges and Bridged Networks - Amendment 29: Cyclic Queuing and Forwarding", IEEE 802.1Qch-2017, DOI 10.1109/IEEESTD.2017.7961303, June 2017. [IEEE802.1Qcr] IEEE, "IEEE Standard for Local and metropolitan area networks -- Bridges and Bridged Networks - Amendment 34: Asynchronous Traffic Shaping", IEEE 802.1Qcr-2020, DOI 10.1109/IEEESTD.2020.9253013, November 2020. [LBF] Clenm, A. and T. Eckert, "High-precision latency forwarding over packet-programmable networks", NOMS 2020 - IEEE/IFIP Network Operations and Management Symposium, April 2020. [LEBOUDEC] Le Boudec, J., "A theory of traffic regulators for deterministic networks with application to interleaved regulators", IEEE/ACM Trans. Networking, vol. 26, no. 6, pp. 2721-2733, doi:10.1109/TNET.2018.2875191, December 2019. [RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification of Guaranteed Quality of Service", RFC 2212, DOI 10.17487/RFC2212, September 1997, . [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI 10.17487/RFC3393, November 2002, . [THOMAS] Thomas, L., Le Boudec, J., and A. Mifdaoui, "On cyclic dependencies and regulators in time-sensitive networks", in Proc. IEEE Real-Time Syst. Symp. (RTSS), York, U.K., pp. 299-311, December 2019. Joung, et al. Expires December 28, 2022 [Page 16] Internet-Draft Asynchronous DetNet Framework June 2022 [Y.3113] International Telecommunication Union, "Framework for Latency Guarantee in Large Scale Networks Including IMT-2020 Network", ITU-T Recommendation Y.3113, February 2021. Authors' Addresses Jinoo Joung Sangmyung University Email: jjoung@smu.ac.kr Jeong-dong Ryoo ETRI Email: ryoo@etri.re.kr Taesik Cheung ETRI Email: cts@etri.re.kr Yizhou Li Huawei Email: liyizhou@huawei.com Peng Liu China Mobile Email: liupengyjy@chinamobile.com Joung, et al. Expires December 28, 2022 [Page 17]