TICTOC Linlang Zhou Internet Draft China Mobile Intended status: Informational July 8, 2009 Expires: January 8, 2010 RAN Synchronization Requirements draft-zhou-tictoc-ran-sync-req-02.txt 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 January 8, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Zhou Expires January 8, 2010 [Page 1] Internet-Draft RAN Synchronization Requirements July 2009 Abstract This Internet draft describes RAN synchronization requirements, mainly about synchronization description and requirements, also includes some applications and problem description. Table of Contents 1. Introduction......................................... 2 2. Applications Description............................... 2 2.1. Time requirements by Service Applications............. 2 2.2. Frequency requirement by Service Applications ......... 3 3. Synchronization Description and Requirements.............. 3 3.1. Network Synchronization ........................... 4 3.1.1. Synchronization Description.................... 4 3.1.2. Minimum Requirements.......................... 4 3.2. Node Synchronization.............................. 4 3.2.1. Synchronization Description.................... 4 3.2.2. Minimum Requirements.......................... 5 4. Security Considerations................................ 5 5. IANA Considerations................................... 5 6. References.......................................... 6 6.1. Normative References.............................. 6 Author's Addresses...................................... 6 1. Introduction RAN has its own synchronization requirements whatever its backhaul is based on IP/MPLS packet switched networks or TDM/ATM links. Besides radio interface synchronization for the NodeB, both Iub and Iu have the same synchronization requirements when is based on packet network. In this RAN synchronization requirements we give some applications description about UTRAN synchronization. Also we list synchronization scenarios in UTRAN and give the detail requirements. 2. Applications Description 2.1. Time requirements by Service Applications There are many applications in telecommunications that need to know the time with great precision. RAN system has to provide precise time synchronization, for there would be some services which require great precision such as position services, streaming services, etc. In TDD mode of 2G/3G systems, in radio interface time synchronization is also needed for smooth handover. Zhou Expires January 8, 2010 [Page 2] Internet-Draft RAN Synchronization Requirements July 2009 2.2. Frequency requirement by Service Applications Cellular base stations require highly accurate frequency synchronization as reference from which they derive transmission frequencies and operational timing however their transport is over E1/T1 or PSN, such as Ethernet IP and MPLS. The radio frequencies should be accurate. To use radio spectrum efficiently transmission frequencies which are allocated to a given base station and its neighbors had better not interfere with each other. There is an additional requirement derived from the need for smooth handover when a mobile station crosses from one cell to another. 3. Synchronization Description and Requirements As to RAN synchronization issues, we may say it include "Network synchronization" "Node Synchronization" "Transport Channel synchronization" "Radio Interface synchronization" "Time Alignment Handling" "Uplink synchronization"[1]. Actually when we mention these six "Synchronization", we mean different synchronization mechanisms in RAN system, and not mean synchronization requirements. AS to RAN synchronization requirements, it can be simpler. We could conclude into only two kinds of synchronization requirements: network synchronization and node synchronization. |-------| |Vocoder| |-------| --- | | |TIME ALIGNMENT | |-------| | | | | | RNC | | |-------| | --- | | NNETOWRK | | | SYNC | |-------| |-------| | NODE | Node | | Node | | SYNC | B | | B | | | |-------| |-------| | | | | | | +-------+ --- --- | | | UE | |-------| Figure 1 RAN SYNC REQUIREMENTS Zhou Expires January 8, 2010 [Page 3] Internet-Draft RAN Synchronization Requirements July 2009 3.1. Network Synchronization 3.1.1. Synchronization Description Network synchronization relates to the distribution of synchronization references to the RAN Nodes and the stability of the clocks in the RAN. This distribution of synchronization references includes the distribution in Iu interface, Iub interface and radio interface. To fulfill the distribution of an accurate frequency reference to the network elements in the UTRAN, network has to provide a synchronization reference with enough frequency accuracy. RNC should be able to pick-up synchronization information from Iu interface. Synchronization of Iub interface is provided from RNC. The clock to be implemented in UTRAN Nodes shall be chosen with characteristics that depend on the adopted L1 or L2 medium. For example in order to support STM-N interfaces at the RNC, the ITU-T Recommendation G.813 (see reference) may be sufficient. But we still have some common requirement for RNC. 3.1.2. Minimum Requirements The reference frequency accuracy of RNC shall be better than or equal to 4.6ppm.When outside reference clock is invalid, system clock of RNC should be able to change into Holdover mode. Output of system clock should be able to hold original phase and accuracy of 4.6ppm. As to Iub and Iu interfaces, different kinds of links and interfaces have different synchronization requirement. For E1 interfaces frequency accuracy should be better than or equal to 50ppm(see reference to ITU-T G.703). For STM-N interfaces frequency accuracy should be better than or equal to 4.6ppm see (reference to ITU-T G.813). For packet switched network frequency accuracy requirement level is not so strict. The frequency accuracy of base stations shall be better than or equal to 0.05ppm on the radio interface whatever based TDD mode or FDD mode. 3.2. Node Synchronization 3.2.1. Synchronization Description Node Synchronization relates to the estimation and compensation of timing difference among RAN nodes. Node synchronization includes two types: "RNC-NodeB" and "Inter NodeB" Node Synchronization. Zhou Expires January 8, 2010 [Page 4] Internet-Draft RAN Synchronization Requirements July 2009 "RNC-NodeB" Node Synchronization allows getting knowledge of the timing differences between RNC and its NodeBs. When there is some position service, "RNC-NodeB" Node Synchronization would be important. "Inter NodeB" Node Synchronization aims to achieve a common timing reference among NodeB's. The achievement of a common timing reference among NodeB's may be used in TDD to support Cell synchronization in order to minimize cross-interference. 3.2.2. Minimum Requirements As to "RNC-NodeB" Node Synchronization, timing accuracy requirement level in packet switched network is not so strict. For example, as to Ethernet, accuracy better than 1ms may be sufficient. If position service is provided, the requirements of "RNC-NodeB" synchronization are to be discussed. "Inter NodeB" Node Synchronization in TDD should be better than or equal to 3us(3GPP TS 25.123). Base station synchronization accuracy is defined as the maximum deviation in frame start times between any pair of base stations on the same frequency that have overlapping coverage areas. If "Inter NodeB" Node Synchronization pick-up radio timing reference from external clock reference, such as GPS, then the timing accuracy requirement between NodeB and reference clock should be better than or equal to 1.5us. If "Inter NodeB" Node Synchronization pick-up radio timing reference from Iu interface, then the timing accuracy requirement between NodeB and reference RNC should be better than or equal to 1.5us. 4. Security Considerations Time and frequency services are critical in RAN. Hence time and frequency transfer services MUST be protected from being compromised. The most significant threat is a false time or frequency server being accepted instead of a true one, thus enabling a hacker to bring down critical services. Protection mechanisms must be deployed and these mechanisms should not degrade the quality of synchronization. 5. IANA Considerations No IANA actions are required as a result of the publication of this document. Zhou Expires January 8, 2010 [Page 5] Internet-Draft RAN Synchronization Requirements July 2009 6. References 6.1. Normative References [1] "Synchronization in UTRAN Stage 2(Release7)", 3GPP TR 25.402 V7.3.0, June 2007. [2] S.Bryant, Y(J).Stein, "TICTOC Problem Statement", January 19, 2007, Author's Addresses LinLang Zhou China Mobile 53A, Xibianmennei Ave. Xuanwu District Beijing China Email: zhoulinlang@chinamobile.com Zhou Expires January 8, 2010 [Page 6]