TICTOC Linlang Zhou Internet Draft China Mobile Intended status: Informational Aug 3, 2007 Expires: January 2008 RAN Synchronization Requirements draft-zhou-tictoc-ran-sync-req-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document may not be modified, and derivative works of it may not be created, except to publish it as an RFC and to translate it into languages other than English, other than to extract section XX as-is for separate use. 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 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract Zhou Expires January 2008 [Page 1] Internet-Draft RAN Synchronization Requirements July 2007 This Internet draft describes RAN synchronization requirements, mainly about synchronization description and requirements, also includes some applications description. 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 RFC-2119. Table of Contents 1. Introduction................................................2 2. Applications Description.....................................3 2.1. Time Service Applications...............................3 2.2. Frequency 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....................................5 3.2.1. Synchronization Description........................5 3.2.2. Minimum Requirements...............................5 3.3. Time Alignment.........................................6 3.3.1. Synchronization Description........................6 3.3.2. Minimum Requirements...............................6 4. Security Considerations......................................6 5. IANA Considerations.........................................6 6. Acknowledgments.............................................6 7. References..................................................7 Author's Addresses.............................................7 Intellectual Property Statement.................................7 Disclaimer of Validity.........................................7 1. Introduction RAN has its own synchronization requirements whatever its backhaul based on IP/MPLS packet switched networks and TDM/ATM links. Besides radio interface synchronization, Iub and Iu have the same synchronization requirements when is based packet network. In this RAN synchronization requirements we give some applications description about RAN synchronization. Also we list synchronization scenario and requirements in RAN. Zhou Expires January 2008 [Page 2] Internet-Draft RAN Synchronization Requirements July 2007 2. Applications Description 2.1. Time Service Applications There are many applications in telecommunications that need to know the time with great precision. If there would be some services that require great precision such as position services, then RAN system has to provide precise time synchronization. In TDD mode of 2G/3G system, radio interface time synchronization is also needed for smooth handover. 2.2. Frequency Service Applications Cellular base-stations require a highly accurate frequency 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, not mean synchronization requirements.AS to RAN synchronization requirements, it can be more simple. We could conclude into only three kinds of synchronization requirements: network synchronizationˇ˘node synchronization and time alignment over Iu interface. Zhou Expires January 2008 [Page 3] Internet-Draft RAN Synchronization Requirements July 2007 +-------+ |Vocoder| |-------| --- | | | |TIME ALIGNMENT | +-------+ | | | | | RNC | | |-------| NETWORK --- | | | | | SYNC NODE +-------+ +-------+ | | Node | | Node | | SYNC | B | | B | | | |-------| |-------| | | | | | | +-------+ --- --- | | | UE | |-------| Figure 1 RAN SYNC REQUIREMENTS 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 L1 adopted. 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 Zhou Expires January 2008 [Page 4] Internet-Draft RAN Synchronization Requirements July 2007 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 L1 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. "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, better than 1ms may be sufficient. If radio timing reference would pick-up time from Iu interface, then "RNC- NodeB" Node Synchronization would be stricter, for example maybe to support 3us. "Inter NodeB" Node Synchronization in TDD should be better than or equal to 3us.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. Zhou Expires January 2008 [Page 5] Internet-Draft RAN Synchronization Requirements July 2007 3.3. Time Alignment over Iu 3.3.1. Synchronization Description Time Alignment over Iu mainly aims to provide an accurate timing reference to Iub or even radio reference. 3.3.2. Minimum Requirements Node Synchronization, timing accuracy requirement level in packet switched network is not so strict. For example as to Ethernet, better than 1ms may be sufficient. But if radio timing reference would pick- up time from Iub through Iu interface, then time alignment over Iu would be stricter, for example maybe to support 3us. 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. Any protection mechanism must be designed in such a way that it does not degrade the quality of the time transfer. 5. IANA Considerations No IANA actions are required as a result of the publication of this document. 6. Acknowledgments Zhou Expires January 2008 [Page 6] Internet-Draft RAN Synchronization Requirements July 2007 7. References [3GPP TR 25.402 V7.3.0] "Synchronisation in UTRAN Stage 2(Release7)", June 2007 [IETF draft-bryant-tictoc-probstat-00]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 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS Zhou Expires January 2008 [Page 7] Internet-Draft RAN Synchronization Requirements July 2007 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Zhou Expires January 2008 [Page 8]