Internet Working Group L. Han Internet-Draft China Mobile Intended status: Informational Y. Jiang J. Xu X. Liu Huawei D. P. Venmani Orange Labs Expires: September 2016 March 21, 2016 Problem Statements of Scalable Synchronization Networks draft-hjxl-scsn-ps-00.txt Abstract With the wide deployment of 4G and beyond mobile networks, a great number of cells need high precision frequency and/or time synchronization for their normal operation. It is crucial to configure and manage the synchronization network in a scalable way, and simplify the monitoring and operation for synchronization networks. This document analyzes the use cases and requirements in synchronization networks, and provides a problem statement for scalable synchronization networks. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 21, 2016. Han and et al Expires September 21, 2016 [Page 1] Internet-Draft Problem Statement of SCSN March 2016 Copyright Notice Copyright (c) 2016 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 (http://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. Table of Contents 1. Introduction .............................................. 2 1.1. Conventions used in this document ...................... 4 1.2. Terminology ............................................ 4 2. Use cases for scalable synchronization network ............ 4 2.1. Synchronization path configuration ..................... 4 2.2. Synchronization OAM .................................... 5 2.3. Synchronization network resiliency ..................... 6 2.4. Multi-layer/Multi-domain synchronization network ....... 6 3. Synchronization Requirements .............................. 7 4. Security Considerations ................................... 7 5. IANA Considerations ....................................... 8 6. References ................................................ 8 6.1. Normative References ................................... 8 6.2. Informative References ................................. 8 7. Acknowledgments ........................................... 9 1. Introduction In modern communication networks, most telecommunication services require that the frequency or phase difference between the whole network equipments should be kept within the reasonable range. Especially for mobile networks, there is a requirement for high precision network clock synchronization, including frequency synchronization and phase synchronization. Han and et al Expires September 21, 2016 [Page 2] Internet-Draft Problem Statement of SCSN March 2016 One focus of the Deterministic Networking (DetNet) Working Group in the IETF is to provide solutions for services with deterministic properties of controlled latency, thus it requires high precision time synchronization among all relay systems in a DetNet network. For packet switching networks, SyncE and IEEE 1588-2008/PTPv2 protocols are widely deployed for frequency and time synchronization respectively in mobile network. Synchronization path planning and provisioning are very complex as so many parameters (e.g., quality level, priority, synchronization enable/disable, hop limit, holdover timeout, and etc) need to be configured. Furthermore, configuration of SyncE must not introduce any loops in the synchronization paths. Hence, deployment of synchronization solutions in networks requires professional skills in synchronization protocols and also the engineering capability in analyzing and planning the network topology. With the deployment of 4G network, the density of cells is explosively growing, as a result, the size of mobile networks and its backhaul network has greatly increased (it may consist of tens of thousands of network equipments in a single metro city nowadays). This scalability requirement will pose a great challenge to realize synchronization, and the management and monitoring of the synchronization network becomes dramatically more complex for service providers. In the past, management and monitoring of synchronization networks are mainly resorted to manual configuration and manual diagnosis, which are complex, error-prone and very time-consuming. Thus it is hard to avoid synchronization loops, erroneous configuration and other mistakes. Therefore, it is important to provide some tools to improve the efficiency of fault monitoring and detection in synchronization networks. As the synchronization is critical for the mobile services, it will beneficial to provide resiliency for synchronization networks, so that synchronization failure can be recovered (even provide protection in the distribution layer, i.e., even when the working path synchronization path is lost, the frequency source is still available from the protection path). Furthermore, as the mobile network size increases dramatically, the synchronization performance is hard to be satisfied, e.g., care must be taken to guarantee that a certain hop limit (e.g. a maximum of 20 hops) of time-distribution from the timing source to a cell site is not exceeded. Han and et al Expires September 21, 2016 [Page 3] Internet-Draft Problem Statement of SCSN March 2016 This document provides some use cases and requirements on configuration and management of a large synchronization network and provides problem statements for the SCalable Synchronization Network (SCSN). 1.1. Conventions used in this document 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 [RFC2119]. 1.2. Terminology OAM: Operation Administration and Maintenance BMCA: best master clock algorithm T-GM: Telecom Grandmaster, a device consisting of a Boundary Clock as defined in [IEEE-1588], with additional performance characteristics defined in [G.8273.2]. 2. Use cases for scalable synchronization network Following are some use cases of SCSN from a management and operation viewpoint. 2.1. Synchronization path configuration In a huge mobile backhaul network with more than 10,000 nodes, manual planning and provisioning of synchronization network are very onerous. For example, manual planning and configuration for a simple network may need more than several weeks; furthermore, it is error-prone. And the planning can't eliminate the risk of introducing loops to a synchronization network. To facilitate synchronization configuration, a controller may be introduced into the SCSN. The controller shall automatically compute, plan and provision the synchronization paths based on the overall physical network topology, thus it can eliminate the risks associated with manual planning. A typical controller for synchronization network can compute and provision a synchronization network with tens of thousands of nodes Han and et al Expires September 21, 2016 [Page 4] Internet-Draft Problem Statement of SCSN March 2016 in just a few minutes, and it is guaranteed that no synchronization loop will be introduced if the algorithm is correctly implemented. Synchronization configuration via a centralized controller requires that the controller be highly efficient, agile and reliable. To accommodate for different types of equipment implementations, a common interface is needed for synchronization network configuration and management, it can further provide the ability to retrieve the network's synchronization configuration and states of a protocol engine in a device. For example, whether the device is locked or not, what is the port state of PTP port (i.e., master, slave or passive), the current port ID associated with a frequency source in syncE, and etc. This capability is essential for the management and maintenance of synchronization networks. 2.2. Synchronization OAM In the maintenance of a huge synchronization network, an operator may encounter various synchronization problems. The traditional manual trouble shooting hop by hop is very onerous. Even if the malfunction equipments are located in a single operator network, the fault detection procedure is very tedious, let alone in the case of network interworking with a third party. Traditionally, synchronization fault detection is done by checking synchronization devices on a path one by one manually, i.e., an operator must login to the device (i.e. the device is adjacent to the fault base station or the device nearest to the base station among the devices with the clock alarm), read the configuration information, status and clock alarms information. After analyzing all the information, if the operator still can't locate the source for the fault, the operator must find the upstream device according to the synchronization status information (i.e. the port state of 1588v2 and the current tracing clock port ID of syncE). The operator must login to each upstream device and check the synchronization information one by one, until the source device of the synchronization fault is found. If the operator cannot locate the fault with the current limited information from the equipments, the operator may have to test the synchronization performance manually by some external instruments. This procedure requires that the operator must have a deep understanding of the synchronization protocols and principle of synchronization engineering. And it also is very time-consuming, and Han and et al Expires September 21, 2016 [Page 5] Internet-Draft Problem Statement of SCSN March 2016 sometimes, detecting a single clock fault may even cost up to ten days. Sometimes, the clock synchronization performance of base station degraded but no clock fault alarm is raised. With synchronization fault detection, an operator cannot locate the true reason of service disruption. In that case, on-demand performance monitoring of a synchronization path may provide the needed information for diagnosis by monitoring the synchronization performance of all devices in the synchronization path if a base station at the end of the path is in problem. Therefore, the functions of synchronization OAM shall include synchronization fault detection and synchronization performance monitoring, both are vital in the diagnosis of a synchronization network. 2.3. Synchronization network resiliency If a synchronization path is broken or degraded, it will seriously influence the clock performance of the synchronization network, and further affect the other services of the mobile network. Thus resiliency of the synchronization network is very important. In general, if allowed by the network topology, the equipment can be provisioned with a working and a protection synchronization path for SyncE in a mobile network. Thus, the equipments in the mobile network can realize synchronization protection with both the working and backup ports. Even when neither the clock signal on the working port nor on the backup port is available (i.e. loss of signal or degrade of SNR (Signal to Noise Ratio)), the equipment shall not lose the timing source if there is connectivity to it. Ideally, the network can restore from the fault by computation of another path with the help of the controller. 2.4. Multi-layer/Multi-domain synchronization network In general, to guarantee the time synchronization accuracy, the suggested maximum hop from the frequency source to the end equipment is 20 in the synchronization network. And the suggested maximum hop from the time source to the end equipment is 30. The maximum values may be defined differently for different operators in different geographies. Han and et al Expires September 21, 2016 [Page 6] Internet-Draft Problem Statement of SCSN March 2016 As tens of thousands of equipments needs to be supported in the same synchronization network, the planning, maintenance and performance of synchronization network face new challenges, for example, the end equipments may hardly satisfy the hop restriction in synchronization. Hierarchical division of a huge synchronization network into multi- layers and/or multi-domains may improve the scalability. For example, the whole synchronization network can be divided into several domains according to their locations. 3. Synchronization Requirements In order to facilitate the provision and management of a large synchronization network, the following requirements need to be addressed in the SCSN: a)The synchronization network should support a generic, vendor- independent and protocol-neutral data model for the synchronization configuration to support heterogeneous networks; b)The synchronization network should support computation and configuration of frequency and time synchronization path; c)The synchronization network should provide high reliability and resiliency to protect and recover from failures in synchronization. d)The synchronization network should provide high scalability, which may require a network to be divided into multiple logical domains, but still maintain a high precision timing signal along a long synchronization path. e)The synchronization network should provide flexible OAM (Operation Administration and Maintenance) functions for synchronization, such as troubleshooting and synchronization performance monitoring, which can be called on demand if the requested timing performance is not met. 4. Security Considerations It will be considered in a future revision. Han and et al Expires September 21, 2016 [Page 7] Internet-Draft Problem Statement of SCSN March 2016 5. IANA Considerations There are no IANA actions required by this document. 6. References 6.1. Normative References [IEEE-1588]IEEE 1588, Precision Clock Synchronization Protocol for Networked Measurement and Control Systems, 2008 6.2. Informative References [G.8261] ITU-T, Timing and synchronization aspects in packet networks, August, 2013 [G.8275] ITU-T, Architecture and requirements for packet-based time and phase distribution, November, 2013 [ptp-mib] Shankarkumar, V., Montini, L., Frost, T., and Dowd, G., Precision Time Protocol Version 2 (PTPv2) Management Information Base, draft-ietf-tictoc-ptp-mib-06, work in progress Han and et al Expires September 21, 2016 [Page 8] Internet-Draft Problem Statement of SCSN March 2016 7. Acknowledgments TBD Authors' Addresses Liuyan Han China Mobile Xuanwumenxi Ave, Xuanwu District Beijing 100053, China Email: hanliuyan@chinamobile.com Yuanlong Jiang Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129, China Email: jiangyuanlong@huawei.com Jinchun Xu Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129, China Email: xujinchun@huawei.com Xian Liu Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129, China Email: lene.liuxian@huawei.com Daniel Philip Venmani Orange Labs 2, avenue Pierre Marzin, Lannion 22307, France Email: danielphilip.venmani@orange.com Han and et al Expires September 21, 2016 [Page 9]