Network Working Group L. Qiang, Ed. Internet-Draft B. Liu Intended status: Informational Huawei Expires: November 30, 2018 L. Geng China Mobile May 29, 2018 Large-Scale Deterministic Network draft-qiang-detnet-large-scale-detnet-00 Abstract This document presents a Large-scale Deterministic Network (LDN) system, which consists of Scalable Deterministic Forwarding (SDF) and Scalable Resource Reservation (SRR). 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 November 30, 2018. Copyright Notice Copyright (c) 2018 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 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. Qiang, et al. Expires November 30, 2018 [Page 1]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 1.2. Terminology & Abbreviations . . . . . . . . . . . . . . . 2 2. Scalable Deterministic Forwarding . . . . . . . . . . . . . . 3 2.1. Three Queues . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Cycle Identifier Carrying . . . . . . . . . . . . . . . . 5 3. Scalable Resource Reservation . . . . . . . . . . . . . . . . 5 4. Performance Analysis . . . . . . . . . . . . . . . . . . . . 6 4.1. Queueing Delay . . . . . . . . . . . . . . . . . . . . . 6 4.2. Jitter . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 8. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction This document presents a Large-scale Deterministic Network (LDN) system, which consists of Scalable Deterministic Forwarding (SDF) and Scalable Resource Reservation (SRR). The technologies of SDF and SRR can be used independently. As [draft-ietf-detnet-problem-statement] indicates, deterministic forwarding can only apply on flows with well-defined traffic characteristics. The traffic characteristics of DetNet flow has been discussed in [draft-ietf-detnet-architecture], that could be achieved through shaping at Ingress node or up-front commitment by application. This document assumes that DetNet flows follow some specific traffic patterns accordingly. 1.1. Requirements Language 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. 1.2. Terminology & Abbreviations This document uses the terminology defined in [draft-ietf-detnet-architecture]. TSN: Time Sensitive Network CQF: Cyclic Queuing and Forwarding Qiang, et al. Expires November 30, 2018 [Page 2]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 LDN: Large-scale Deterministic Network SDF: Scalable Deterministic Forwarding SRR: Scalable Resource Reservation DSCP: Differentiated Services Code Point EXP: Experimental T: the length of a cycle H: the number of hops K: the size of aggregated resource reservation window 2. Scalable Deterministic Forwarding DetNet aims at providing deterministic service over large scale network. In large scale network, it is difficulty to get precise time synchronization among numerous and diverse devices. As a compromise, this document assumes that just clock synchronization is required among devices. That is different devices maintain the same clock frequency 1/T, but may at the different time as shown in Figure 1. <-----T-----> <-----T-----> | | | | | | Node A +-----------+-----------+ Node A +-----------+-----------+ | | | | | | Node B +-----------+-----------+ Node B +-----------+-----------+ (i) time synchronization (ii) clock synchronization Figure 1: Time Synchronization & Clock Synchronization IEEE 802.1 CQF is an efficient forwarding mechanism in TSN that guarantees bounded end-to-end latency. CQF is designed for limited scale network, the time synchronization is required, and the link propagation delay is required to be smaller than a cycle length T. Considering the large scale network deployment, the proposed Scalable Deterministic Forwarding (SDF) permits clock synchronization and link propagation delay may exceed T. Besides these two points, CQF and the asynchronous forwarding are very similar. Qiang, et al. Expires November 30, 2018 [Page 3]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 Figure 2 compares them through an example. Suppose Node A is the upstream node of Node B. In CQF, packets sent from Node A at cycle x, will be received by Node B at the same cycle, then further be sent to downstream node by Node B at cycle x+1. Due to long link propagation delay and clock synchronization, Node B will receive packets from Node A at different cycle denoted by y in the SDF, and Node B swaps the cycles carried in packets with y+1, then sends out those packets at cycle y+1. This kind of cycle mapping (e.g., x <--> y+1) exists between any pair of neighbor nodes, can be studied through just once forwarding. With this mapping, the receiving node can easily figure out when the received packets should be send out, the only requirement is to carry the cycle identifier of sending node in the packets. | cycle x | cycle x+1 | | cycle x | cycle x+1 | Node A +-----------+-----------+ Node A +-----------+-----------+ \ \ \packet \packet \receiving \receiving \ \ | V | cycle x+1 | | V | cycle y+1| Node B +-----------+-----------+ Node B +-----------+-----------+ cycle x \packets cycle y \packets \sending \sending \ \ \ \ V V (i) CQF (ii) SDF Figure 2: CQF & SDF 2.1. Three Queues In CQF each port needs to maintain 2 (or 3) queues for each class of flows, one is used to buffer newly received packets, another one is used to store the packets that are going to be sent out, one more queue may be needed to avoid output starvation [scheduled-queues]. While in SDF, at least 3 queues are needed. As Figure 3 illustrated, a node may receive packets sent at two different cycles from a single upstream node due to the clock synchronization. Following the timing slot mapping (i.e., x <--> y+1), packets that carry cycle identifier x should be send out by Node B at cycle y+1, and packets that carry cycle identifier x+1 should be send out by Node B at cycle y+2. Therefore, two queues are needed to store the newly received packets, as well as one queue to Qiang, et al. Expires November 30, 2018 [Page 4]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 store the sending packets. In order to absorb jitter, more queues also might be necessary. | cycle x | cycle x+1 | Node A +-----------+-----------+ \ \ \ \packet \ \receiving | V V | | Node B +-----------+-----------+ cycle y cycle y+1 Figure 3: Three Queues in SDF 2.2. Cycle Identifier Carrying As former two sections explained, cycle identifier needs to be carried in packet, so that an appropriate queue can be selected accordingly. That means 2 bits is needed in the three queues model of SDF, in order to identify different cycles between a pair of neighbor nodes. There are several ways to carry this 2 bits cycle identifier, for example: o DSCP of IPv4 Header o Traffic Class of IPv6 Header o EXP of MPLS Header o EtherType of Ethernet Header o IPv6 Extension Header o TLV of SRv6 o EXP of MPLS-SR Header 3. Scalable Resource Reservation SDF must work with some resource reservation mechanisms, that can be the proposed Scalable Resource Reservation (SRR) or other mechanisms. Resource reservation guarantees the necessary network resources when deterministic flows are scheduled. Network nodes have to record how many network resources are reserved for a specific flow from when it starts to when it ends (e.g., <flow_identifier, reserved_resource, start_time, end_time>). Maintaining per-flow resource reservation status may be acceptable to edge nodes, but un-acceptable to core Qiang, et al. Expires November 30, 2018 [Page 5]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 nodes. [draft-ietf-detnet-architecture] pointed out that aggregation must be supported for scalability. [Details of SRR is TBD.] 4. Performance Analysis 4.1. Queueing Delay End-to-end queueing delay's expectation is 1.5*T*H, where H is the number of hops. [Detailed Analysis is TBD] 4.2. Jitter Jitter's upper bound is 2*T. [Detailed Analysis is TBD] 5. IANA Considerations This document makes no request of IANA. 6. Security Considerations Security issues have been carefully considered in [draft-ietf-detnet-security]. More discussion is TBD. 7. Acknowledgements TBD. 8. Normative References [draft-ietf-detnet-architecture] "DetNet Architecture", <https://datatracker.ietf.org/doc/ draft-ietf-detnet-architecture/>. [draft-ietf-detnet-dp-sol] "DetNet Data Plane Encapsulation", <https://datatracker.ietf.org/doc/ draft-ietf-detnet-dp-sol/>. [draft-ietf-detnet-problem-statement] "DetNet Problem Statement", <https://datatracker.ietf.org/doc/ draft-ietf-detnet-problem-statement/>. Qiang, et al. Expires November 30, 2018 [Page 6]
Internet-Draft Supervised Heterogeneous Network Slicing May 2018 [draft-ietf-detnet-security] "DetNet Security Considerations", <https://datatracker.ietf.org/doc/ draft-ietf-detnet-security/>. [draft-ietf-detnet-use-cases] "DetNet Use Cases", <https://datatracker.ietf.org/doc/ draft-ietf-detnet-use-cases/>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [scheduled-queues] "Scheduled queues, UBS, CQF, and Input Gates", <http://www.ieee802.org/1/files/public/docs2015/ new-nfinn-input-gates-0115-v04.pdf>. Authors' Addresses Li Qiang (editor) Huawei Beijing China Email: qiangli3@huawei.com Bingyang Liu Huawei Beijing China Email: liubingyang@huawei.com Liang Geng China Mobile Beijing China Email: gengliang@chinamobile.com Qiang, et al. Expires November 30, 2018 [Page 7]