Internet DRAFT - draft-hjxl-scsn-ps

draft-hjxl-scsn-ps



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]