Aviat Networks, Inc. · NASDAQ:AVNW
Aviat Networks — Technical Presentation (October 2010)
32 slides from Aviat Networks's technical presentation, October 2010
Slide 1: Clock Synchronization in Cellular/Mobile Networks
CLOCK SYNCHRONIZATION IN CELLULAR/MOBILE NETWORKS P E T E R C R OY S E N I O R N E T W O R K A R C H I T EC T AV I AT N E T W O R K S 1
Slide 2: Agenda
Agenda • Sync 101: Frequency and phase synchronization basics • ‘Legacy sync’: GPS and SDH/Sonet overview • Q&A part 1: Sync 101 & Legacy sync • Summary of packet sync standards • Sync in cellular/mobile networks: Overview and challenges • Impact of sync on backhaul networks migration • Summary • Q&
Slide 3: Classical Music Example
Classical Music Example Question: What do we need to make a lot of instruments play a classical symphony? 3 AVIAT NETWORKS | October 2010
Slide 4: Synchronizing an Orchestra
Synchronizing an Orchestra Answer: A conductor with a baton. 4 AVIAT NETWORKS | October 2010
Slide 5: Synchronization in Telecommunications
Synchronization in Telecommunications Master The network master clock is Clock playing the role of the (PRC) orchestra conductor, so the independent cellular network users can transmit and receive wireless data at the same rate. We call this clock the network Primary Reference Clock (PRC) or stand a
Slide 6: Clock Signal Phase Definitions
Clock Signal Phase Definitions • Phase relations between two clock signals Clocks are in phase, signals are perfectly aligned: Clock frequency and phase are synchronized Clocks have an accumulating phase offset: This is a frequency accuracy problem! Clocks have a changing phase offset: This is a fre
Slide 7: Clock Signal Quality Definitions
Clock Signal Quality Definitions • Frequency offset: Average phase change accumulated within a 100 seconds observation period example foffset = Δt/t = 1ns / 100s = 10‐11 7 AVIAT NETWORKS | October 2010
Slide 8: Clock Signal Quality Definitions
Clock Signal Quality Definitions • Frequency accuracy: MTIE (maximum time interval error) is the largest phase change during the observation interval. Note: MTIE only increases and hides periods of small errors 8 AVIAT NETWORKS | October 2010
Slide 9: Clock Signal Quality Definitions
Clock Signal Quality Definitions • Time domain stability uses statistical observations of frequency sources over observation time - Deviations from a nominal value are expressed with statistical methods - TDEV (time deviation, calculated from ‘Allan Deviation’) characterizes the statistical time err
Slide 10: Network Synchronization Standards
Network Synchronization Standards • The ITU has released numerous recommendations to define clock accuracy & quality requirements for networks • TDM transport networks have used clock synchronization for decades to ensure correct data transmission Requirements SDH/PDH Network Packet Network Function
Slide 11: Network Synchronization using GPS
Network Synchronization using GPS • GPS system uses synchronized atomic clocks on the ground and in the satellites to measure time differences of coded signals to determine a position on earth • The frequency and phase synchronized GPS system clock can be received and used to sync a local oscillator
Slide 12: GPS Receiver Clock Sync: Pro's and Con's
GPS Receiver Clock Sync: Pro’s and Con’s • Pro’s + Very accurate sync of frequency & phase plus time/day (UTC) + Equivalent to distributed PRC clocks + Relatively inexpensive receivers • Con’s - Additional outdoor antenna installation required - Vulnerable to local interference and malicious radio j
Slide 13: Legacy Sync: SDH/Sonet & PDH Networks
Legacy Sync: SDH/Sonet & PDH Networks • Circuit switched networks are per definition synchronized - SDH/Sonet defines synchronous transmit/receive data clocks for transmission - PDH hierarchy is derived from SDH/Sonet clock timing (plesiochronous clock) - PDH circuits (E1/T1, etc.) use HDB3 coded si
Slide 14: Legacy Sync: SDH/Sonet & PDH Networks Pro's and Con's
Legacy Sync: SDH/Sonet & PDH Networks • Pro’s + Very accurate sync delivered through physical layer + Ubiquitously available throughout the transmission network + Well established and understood (e.g. trouble‐shooting) • Con’s - Frequency only sync; Phase sync separately needed - PDH circuits scalab
Slide 15: Q&A Sync 101 & Legacy Sync
Q&A SYNC 101 & LEGACY SYNC • Questions, comments on synchronization basics? • What legacy sync method is your network using? • Are your network sync requirements changing?
Slide 16: New Standards: Packet Network Synchronization
New Standards: Packet Network Synchronization • Fixed and mobile network operators are migrating from circuit towards packet‐based transport for scalability and cost reasons - But: Packet transport is typically based on asynchronous clocks, i.e. independent clocks for transmitting and receiving stat
Slide 17: Synchronous Ethernet: A Brief History
Synchronous Ethernet: A Brief History • The first attempt to investigate time synchronization over packet networks dates back to ITU Study Group 15, Question 13 in October 2003 – Subsequently became the ITU G.pactiming project • Synchronous Ethernet PHY was initially proposed by British Telecom and
Slide 18: Synchronous Ethernet
Synchronous Ethernet Principle of Ethernet Synchronization Source: ITU G.8261 document Switch A Switch B Switch C MAC MAC MAC PRC clock PHY PHY PHY S M S M S Ethernet connections (electrical/optical) Example: Switch A transports data & clock over the PHY links to switch C ‐‐> Ethernet ports are Mast
Slide 19: Synchronous Ethernet: Pro's and Con's
Synchronous Ethernet: Pro’s and Con’s • Pro’s – Very accurate sync at physical layer (like SDH/Sonet) – Accuracy unaffected by traffic load • Con’s – Frequency only sync; Phase sync separately needed – Requires all switches and routers along the transmission path to support Synchronous Ethernet 19 A
Slide 20: Packet Sync IEEE 1588v2: A Brief History
Packet Sync IEEE 1588v2: A Brief History • IEEE working group was setup in 2001 after prototype work from vendors showed successes • Original version 1 released in 2002, but lacked robustness, accuracy; It was multicast only and frames were long and sent infrequently • Version 2 was released in 2008
Slide 21: IEEE 1588v2 Overview
IEEE 1588v2 Overview • IEEE 1588v2 uses hardware time‐stamped messages to distribute time information between Master and Slaves • The Best Master Clock Algorithm (BMCA) is used to determine the clock sync hierarchy in the 1588v2 domain • Standard does not specify the clock recovery algorithm for sla
Slide 22: IEEE 1588v2 Clock Timing Calculations
IEEE 1588v2 Clock Timing Calculations • 1588v2 is highly sensitive to delay variation of packets and to asymmetries in the transmit/receive path! 22 AVIAT NETWORKS | October 2010
Slide 23: IEEE 1588v2: Pro's and Con's
IEEE 1588v2: Pro’s and Con’s • Pro’s + Frequency and phase sync along time/day are provided + Relatively simple hardware implementation • Con’s - Accuracy varies with traffic load across the network path - Requires symmetrical transport and low delay variation - Equipment of different vendors does n
Slide 24: IETF NTP: A brief history
IETF NTP: A brief history • Network Time Protocol (NTP) is in use since 1985 and is currently in version 4 (NTPv4) • It computes UTC time from a hierarchy of clock sources, Stratum‐1 being the most accurate (atomic clocks), Stratum‐2 and Stratum‐3 derived and synchronized to Stratum‐1 master • NTPv4
Slide 25: IETF NTP: Pro's and Con's
IETF NTP: Pro’s and Con’s • Pro’s + Well established algorithm for timing offset calculations • Con’s - Accuracy varies with traffic load across the network path - Requires very accurate (expensive) local oscillators - Originally designed only for computer clock synchronization 25 AVIAT NETWORKS | O
Slide 26: Cellular/Mobile Base Station Sync
Cellular/Mobile Base Station Sync BTS2 drifts outside 50ppb window F 1 + f2 +/‐ 50ppb BTS 2 Mobile cannot lock to BTS2 and call is dropped F1 +/‐ 50ppb BTS 1 T1 T2 Time • Handset moves from BTS1 coverage area to BTS2 • Traffic to/from the core network needs the exact same timing, otherwise the hands
Slide 27: Cellular/Mobile Radio Sync Requirements
Cellular/Mobile Radio Sync Requirements Frequency Synchronization Mobile Network Frequency Time/Phase TA=1/fA Architecture Sync Sync A t TB=1/fB CDMA2000 9 B fA=fB t GSM 9 UMTS-FDD 9 Phase Synchronization TA=1/fA LTE-FDD 9 A t TB=1/fB UMTS-TDD 9 9 B fA=fB t LTE-FDD with MBMS- 9 9 Single Freq. Networ
Slide 28: Clock Frequency Accuracy Requirements
Clock Frequency Accuracy Requirements • In cellular/mobile applications, the frequency accuracy on the air interface must remain within 50 ppb for seamless handover of mobile devices between radio base stations - 50pbb applies at the radio/antenna interface • Transport nodes in a synchronization cha
Slide 29: Synchronization Transport Chain for 2G/3G/LTE
Synchronization Transport Chain for 2G/3G/LTE PRC Core Transport Network BTS1 BTS2 BTS3 RNC M S S M S M S M S x pbb y pbb z pbb Transport chain accuracy x+y+z<50pbb against PRC • Daisy chained synchronization accuracy decreases with the number of transport network hops • Tighter clock accuracy per h
Slide 30: Complexity of Transport Network Migration
Complexity of Transport Network Migration BTS config in 2010: BTS config in 2012: 2G: E1/T1 2G: E1/T1 (converted to IP) 3G Voice: E1/T1 3G/HSPA: IP/Ethernet (no sync) HSPA: IP/Ethernet (no sync) LTE: IP/Ethernet (sync+phase) Network Migration Progress • Keeping clock sync from SDH/PDH circuits may h
Slide 31: Summary of Synchronization
Summary of Synchronization • Precise and synchronized frequency oscillators are essential for modern telecommunication systems • Traditional TDM transmission systems inherently provides hierarchical clock synchronization • Cost pressures and capacity limits of TDM networks accelerate move to asynchr
Slide 32: Thank You! Time for Your Questions
THANK YOU! TIME FOR YOUR QUESTIONS… pete r. croy@aviat net.com
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