Holdover in synchronization applications: Difference between revisions

Revision as of 14:58, 12 September 2011

Revision as of 15:02, 12 September 2011

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Holdover is important for E911 for example. Most critical telecom applications require precise time and frequency and synchronization to operate properly such as VoIP, video streaming, TDM (time division multiplex) services, voice switching, mobile services, and any LBS (___location based services, with E911 being the most important).<ref>http://www.eetimes.com/design/communications-design/4213947/Understanding-the-concepts-of-synchronization-and-holdover</ref>

1us for synchrophasors <ref>http://tf.nist.gov/general/pdf/2193.pdf</ref>

==How GPS Derived Timing Can Fail==

GPS is sensitive to jamming etc because the signal levels are so low <ref>tf.nist.gov/sim/2010_Seminar/SIM_2010_GPS_Lombardi.ppt</ref>

GPS outage not initially an issue because clocks can go into Holdover <ref>http://www.syncuniversity.org/drsync/q45.php</ref>

GPS suffers from interference which can be alleviated by a GPSDO, up to the stability of the GPSDO<ref>http://www.gmat.unsw.edu.au/snap/publications/khan&dempster2007b.pdf</ref>

==Defining Holdover==

[[Synchronization]]

Clock Accuracy in MIL-PRF-55310<ref>http://standards.gsfc.nasa.gov/reviews/mil/mil-prf-55310d/mil-prf-55310d.pdf</ref>

Time Error Model in ITU G.810<ref>http://www.itu.int/rec/T-REC-G.810-199608-I</ref>

Definition of Holdover<ref>http://www.etsi.org/deliver/etsi_i_ets/300400_300499/30046201/01_60/ets_30046201e01p.pdf</ref>

Definition of Holdover

Definition of a Disciplined Oscillator<ref>http://tf.nist.gov/general/enc-d.htm</ref>

==Holdover Performance Aspects==

Two independent clocks once synchronized will walk away from one another without limit. How fast this happens depends on the quality of the oscillator