Network Working Group Y. Jiang X. Liu Internet-Draft Huawei L. Geng Intended status: Informational China Mobile D. P. Venmani Orange Labs Expires: September 2016 March 21, 2016 Gap Analysis of Scalable Synchronization Networks draft-jiang-scsn-gap-analysis-00.txt Abstract This draft provides a gap analysis for the Scalable Synchronization Networks (SCSN). The document provides an overview of the existing standardization work on synchronization solutions, and outlines some of the important features with regard to scalability that are still missing in current 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. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. Jiang and et al Expires September 21, 2016 [Page 1] Internet-Draft SCSN Gap Analysis March 2016 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 ...................... 3 1.2. Terminology ............................................ 3 2. Related Standardization Work on Synchronization Network ... 4 2.1. A Survey of ITU-T work ................................. 4 2.2. A Survey of IEEE work .................................. 5 2.3. A Survey of IETF work .................................. 6 3. Discussions ............................................... 6 4. Security Considerations ................................... 7 5. IANA Considerations ....................................... 7 6. References ................................................ 7 6.1. Informative References ................................. 7 7. Acknowledgments ........................................... 9 1. Introduction Traditionally, telecommunication systems rely heavily on accurate frequency and/or time synchronization for their proper working. This is especially true for the case of cellular networks (3G, 4G/LTE, etc.), where base stations need accurate and stable frequency clocks in order to obtain their carrier radio frequencies, arbitrate the frequency-shared and time-shared access of terminals, coordinate the handover of terminals between adjacent cells, and etc. Over the years, time-division multiplexing (TDM) transmission technologies such as SDH are used to provide frequency distribution, typically by provisioning a tree-based hierarchy of clocks over the transport network beforehand. Due to the advantages of higher flexibility, lower operation costs, economies of scale and better integration with higher layer IP-based services, telecommunication operators are migrating their networks from TDM technology to packet- Jiang and et al Expires September 21, 2016 [Page 2] Internet-Draft SCSN Gap Analysis March 2016 switching technology, and evolving to "all-IP" architecture. As a result, Synchronous Ethernet (SyncE) is proposed to integrate synchronization distribution capabilities into packet switching systems. Similar to SDH nodes, a SyncE node can acquire the reference clock from the signal received from a specific input port, use it to correct the local clock, and regenerate frequency in the signals transmitted over the output ports. Following this, IEEE 1588-2008/PTPv2 has been specified which provides time synchronization capabilities. This draft analyzes the existing works on synchronization solutions and provides a non-exhaustive list of them. This includes the synchronization solutions developed for telecom networks and other industries as well including but not limited to power generation and transmission industries, finance and trading, scientific computing, road traffic control, and etc., It outlines some of the missing features with regard to scalability that are important for synchronization networks. The aim of this document is to provide guidance for some further synchronization work in the IETF. 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 AVB audio/video bridging BMCA Best Master Clock Algorithm MIB Management Information Base NTP Network Time Protocol OAM Operation Administration and Maintenance PTP Precision Time Protocol PTPv2 Precision Time Protocol Version 2 Jiang and et al Expires September 21, 2016 [Page 3] Internet-Draft SCSN Gap Analysis March 2016 SDH Synchronous Digital Hierarchy SMIv2 Structure of Management Information Version 2 SNTP Simple Network Time Protocol SSM Synchronization Status Message TDM Time Division Multiplex UDP User Datagram Protocol 2. Related Standardization Work on Synchronization Network 2.1. A Survey of ITU-T work ITU-T has approved a series of Recommendations to transport and distribute synchronization over telecom networks. It describes different aspects of synchronization in a TDM network. [G.803] specifies the SDH-based synchronization network architecture. Based on the architecture, [G.781] specifies synchronization principles and defines synchronization layer functions which obey the combination rules given in [G.783] to specify synchronization functionality of network elements. [G.823], [G.824] and [G.825] specify the maximum network limits of jitter and wander and the minimum equipment tolerance to jitter and wander respectively for networks based on the 2048 Kbit/s hierarchy, 1544 Kbit/s hierarchy and SDH. Moving forward, ITU-T approved SyncE, a physical layer method, which uses synchronous physical layer for the transport and distribution of frequency over a packet network. [G.8261], [G.8262] and [G.8264] describe the physical layer frequency distribution in packet-based networks. [G.8261] focuses on the distribution of synchronization network clock signals (PNT domain) and of service clock signals (CES domain) over a packet network. It also defines network limits of jitter and wander for the synchronous Ethernet interface. Its latest amendment 1 adds the network jitter limits for several kinds of multilane interfaces consisting of 10G lanes and of 25G lanes. [G.8262] defines the synchronous Ethernet Equipment Clock as well as its requirements for clocks, e.g., bandwidth, frequency accuracy, holdover and noise generation. [G.8264] defines the SSM protocol and formats for SyncE as well as the Ethernet Synchronization Messaging Channel (ESMC). Its latest amendment 1 adds text to describe the ESMC operation with link aggregation. On the other hand, [G.8263] and [G.8265] describe the packet-based mechanisms based on IEEE 1588 to transport frequency over a packet Jiang and et al Expires September 21, 2016 [Page 4] Internet-Draft SCSN Gap Analysis March 2016 network in the absence of physical layer timing. [G.8265] describes the master-slave architecture and requirements for packet-based frequency distribution in telecom networks. According to the architecture, [G.8263] outlines minimum requirements, e.g., frequency accuracy, noise generation, packet delay variation noise tolerance and holdover, for the packet slave clocks. [G.8265.1] further defines a PTP telecom profile for frequency distribution using only unicast mode leaving the use of mixed unicast/multicast operation for further study. PTPv2 was developed based on IEEE 1588-2008 for the transport of phase and time. [G.8271] presents the need for time and phase synchronization in a carrier environment and specifies the time-phase synchronization methods and interfaces as well as its related performance. The architecture and requirements for packet-based time and phase distribution using PTP is described in [G.8275]. According to the architecture, [G.8275.1] defines the PTP profile for telecom networks for time and phase distribution. 2.2. A Survey of IEEE work [IEEE 1588] defines the PTP protocol to synchronize Wide Area Networks. It includes synchronization methodology, datasets and state machine maintained by each clock, to synchronize clocks of distributed nodes in a system using packet-based networks and the Best Master Clock Algorithm (BMCA). It allows all nodes to synchronize system-wide in the sub-microsecond range. Its second version [IEEE 1588-2008] enhances the usability and precision for large networks by defining shorter synchronization frames, mappings to UDP/IP and other protocols, options for redundancy and fault tolerance, and by specifying message extensions using TLV, asymmetry corrections and optional unicast messaging in addition to multicast. It provides flexible configuration by means of configuration sets known as "profiles" used by specific devices to guarantee the proper behavior and performance. Its latest revision [IEEE 1588-20XX] currently under development defines optional data sets required by PTP options, complements the description about granting port operations and about using an alternate timescale, and introduces an optional mechanism for external configuration for a node's port state. It permits synchronization accuracies better than 1 ns. Definitions of a common MIB enabling the use of 1588 in a heterogeneous environment and a link state protocol used to establish redundant synchronization path are currently under study. [IEEE 802.1AS] specifies synchronization based on [IEEE 1588-2008] in Audio/Video Bridging (AVB) networks. It defines a PTP profile with the time-aware bridge acting as boundary clock and time-aware end Jiang and et al Expires September 21, 2016 [Page 5] Internet-Draft SCSN Gap Analysis March 2016 station acting as ordinary clock. The BMCA specified in this standard is an alternate BMCA which is similar but not identical to that specified in [IEEE 1588-2008]. This standard also defines a complete SMIv2 Management Information Base (MIB) set for all features it specifies. Its revision [IEEE 802.1ASbt/D0.7] enhances support for redundant grandmasters and/or paths using multiple gPTP domains, link aggregation and new media types with additional parameter sets for non-Audio/Video applications. Its latest revision [IEEE 802.1AS-Rev] enhances the way needed for a port to determine whether its neighbor is asCapable in a particular domain by adding the per-port global variable tmFtmSupport. Details about redundancy-related definitions, functions and algorithms are currently under study. 2.3. A Survey of IETF work [RFC5905] defines the Network Time Protocol version 4 (NTPv4), which is widely used to synchronize system clocks among a set of distributed time servers and clients with potential accuracies in the low microseconds range. NTPv4 obsoletes both [RFC1305] (NTPv3) and [RFC4330] (SNTP)) and describes the core architecture, protocol, state machines, data structures and algorithms. [draft-ietf-tictoc-ptp-mib-06] defines some managed objects used for managing PTP devices of IEEE 1588 including the ordinary clock, transparent clock, boundary clocks. But this MIB is read-only and not intended to provide the ability to configure PTP clocks. 3. Discussions With the worldwide deployment of 4G/LTE networks, we have already seen tens of thousands of network nodes deployed in a single metro network. In the future, 5G mobile networks will have a greater number of cells and it is expected that the backhaul network will grow even larger. Therefore, the computation of distribution path and configuration for such a large synchronization network will pose a great challenge. Until now, little work has been done on the scalability of synchronization. SyncE work is focused on the general synchronization requirements and architecture (TDM and packet network), it is assumed that a loop-free distribution path will be computed for each end node externally and configured beforehand. Though Synchronization Status Message (SSM) message provides some indication on the quality of the synchronization signal, it cannot locate a fault in synchronization path. Thus, it mainly resorts to onerous, error-prone and time- consuming manual operations at present. Jiang and et al Expires September 21, 2016 [Page 6] Internet-Draft SCSN Gap Analysis March 2016 In IEEE 1588, each node can automatically compute and select synchronization source based on knowledge of the network topology in a domain, but it is difficult to compute and configure a large network in such a distributed manner. Furthermore, it is also assumed that the network operator has assigned specific ports for synchronization. IEEE 1588 does not provide fault diagnosis capability, and resilience is realized by automatic re-computation of a new distribution path based on the new converged network. Therefore, it is crucial to provide a synchronization path computation, configuration and restoration tools for a large synchronization network, and provide necessary OAM tools for its diagnosis. These tools must be generic, vendor-independent and protocol-neutral. 4. Security Considerations This document analyzes the standardization work on synchronization in different SDOs. As no solution is proposed in this document, no security concerns are raised. 5. IANA Considerations There are no IANA actions required by this document. 6. References 6.1. Informative References [RFC1305] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation and Analysis", RFC 1305, March 1992 [RFC4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI", RFC 4330, January 2006 [RFC5905] Mills, D., "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, June 2010 [G.803] ITU-T, Architecture of transport networks based on the synchronous digital hierarchy (SDH), March, 2000. Jiang and et al Expires September 21, 2016 [Page 7] Internet-Draft SCSN Gap Analysis March 2016 [G.823] ITU-T, The control of jitter and wander within digital networks which are based on the 2048 Kbit/s hierarchy, March, 2000. [G.824] ITU-T, The control of jitter and wander within digital networks which are based on the 1544 Kbit/s hierarchy, March, 2000. [G.825] ITU-T, The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH), March, 2000. [G.781] ITU-T, Synchronization layer functions, September, 2008. [G.783] ITU-T, Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks, March, 2006. [G.8261] ITU-T, Timing and synchronization aspects in packet networks, August, 2013. [G.8262] ITU-T, Timing characteristics of synchronous Ethernet equipment slave clock (EEC), January, 2015. [G.8263] ITU-T, Timing characteristics of packet based equipment clocks, February, 2012. [G.8264] ITU-T, Distribution of timing information through packet networks, May, 2014. [G.8265] ITU-T, Architecture and requirements for packet-based frequency delivery, October, 2010. [G.8265.1] ITU-T, Precision time protocol telecom profile for frequency synchronization, July, 2014. [G.8271] ITU-T, Time and phase synchronization aspects of packet networks, February, 2012. [G.8275] ITU-T, Architecture and requirements for packet-based time and phase distribution, November, 2013. [G.8275.1] ITU-T, Precision time protocol telecom profile for phase/time synchronization with full timing support from the network, July, 2014. [IEEE-1588] IEEE, Precision Clock Synchronization Protocol for Networked Measurement and Control Systems, July, 2008. Jiang and et al Expires September 21, 2016 [Page 8] Internet-Draft SCSN Gap Analysis March 2016 [IEEE 802.1AS] IEEE, Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks, March, 2011. [IEEE 802.1ASbt/D0.7] IEEE, Timing and Synchronization for Time- sensitive Applications, November, 2014. [IEEE 802.1AS-Rev/D2.0] IEEE, Timing and Synchronization for Time- Sensitive Applications, October, 2015. [draft-ietf-tictoc-ptp-mib-06] IETF, Precision Time Protocol Version 2 (PTPv2) Management Information Base, work in progress. 7. Acknowledgments TBD Authors' Addresses Yuanlong Jiang Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129, China Email: jiangyuanlong@huawei.com Xian Liu Huawei Technologies Co., Ltd. Bantian, Longgang district Shenzhen 518129, China Email: lene.liuxian@huawei.com Liang Geng China Mobile Xuanwumenxi Ave, Xuanwu District Beijing 100053, China Email: gengliang@chinamobile.com Daniel Philip Venmani Orange Labs 2, avenue Pierre Marzin, Lannion 22307, France Email: danielphilip.venmani@orange.com Jiang and et al Expires September 21, 2016 [Page 9]