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Application note ZLAN-442

Crystals and oscillators for next generation timing solutions

view or download PDF file for Application note ZLAN-442

Physical Layer Synchronization (click for details)

The oscillator requirements for physical layer synchronization are well defined in a variety of ITU-T and ATIS specifications. Namely

Freerun accuracy – lifetime;

Holdover stability – drift under constant temperature conditions, which includes ageing;

Holdover stability – frequency variation due to variable temperature;

Wander generation (MTIE & TDEV), for the respective filter cut-off frequency, under constant temperature conditions;

Wander generation (MTIE & TDEV), for the respective filter cut-off frequency, under variable temperature conditions.

The following are the general classifications used in this document

Class A1. Used with 3 mHz filter bandwidth for compliance with E1-based ITU-T G.812 Type I (SSU) requirements.

Class A2. Used with 1 mHz filter bandwidth for compliance with T1-based Stratum 3E & ITU-T G.812 Type III specifications. Note these oscillators may NOT be

compliant with 3 mHz filter bandwidth E1-based ITU-T G.812 Type I (SSU) requirements.

Class C2. Used with 0.1 Hz and higher filter bandwidths for compliance with T1-based hierarchy specifications such as ITU-T G.813 option 2 SEC, ITU-T G.8262

option 2 EEC, Stratum 3 for SONET, Stratum 3 & SMC. Note these oscillators may NOT be compliance with Class D requirements for E1-Based hierarchy specifications

such as ITU-T G.813 option 1 SEC and ITU-T G.8262 option 2 EEC (specifically frequency stability at constant temperature).

Class D. Used with 1 Hz and higher filter bandwidths for compliance with E1-based hierarchy specifications such as ITU-T G.813 option 1 SEC, ITU-T G.8262 option 2 EEC.

Class E. Used with 14 Hz and higher filter bandwidths for T1-based, E1-based and OTN line card use cases. Class E also used for Clock Synthesis applications.

Details on the test equipment, procedures and test-setups for qualifying oscillators can be found in ZLAN-472 (covering both Stratum 3 and Stratum 3E).

Oscillators For Physical Layer Synchronization

CLASSIFICATION

Below list is a summary of the various classifications of oscillator for use in physical layer synchronization and protocol layer synchronization. Some classifications represent the superset requirements of closely related clocks (where an individual clock requirement may be less than that listed for the superset).

CLASS A2

Used with 1 mHz filterbandwith for complience with T1-based Stratum 3E & ITU-T G.812 Type III specifications. Note these oscillators may NOT be compliant with class A1, used for 3 mHz filter bandwidth E1-based ITU-t G.812 Type I (SSU) requirements

OCXOs for CLASS A2

CLASS C2

Used with 0.1 Hz and higher filter bandwidths for compliance with T1-based hierarchy specifications such as ITU-T G.813 option2 SEC, ITU_T G.8262 option2 EEC, stratum 3 for SONET, Stratum 3 & SMC. Note these oscillators may NOT be compliance with Class D requirements for E1-Based hierarchy specifications such as ITU-T G.813 option 1 SEC and ITU-T G.8262 option 2 EEC (specifically frequency stability at constant temperature)

OCXOs for CLASS C2

TCXOs for CLASS C2

CLASS D

Used with 1 Hz and higher filter bandwidths for compliance with E1-based hierarchy specifications such as ITU-T G.813 option 1EEC

OCXOs for CLASS D

TCXOs for CLASS D

CLASS E

Used with 14 Hz and higher filter bandwidths for T1-based,E1-based and OTN line card use cases.Also listed are oscillators/crystals for Clock Synthesis applications

CLOCK OSCILLATORS for CLASS E

CRYSTALS for CLASS E

Protocol Layer Synchronization (click for details)

The oscillator requirements for protocol layer synchronization are not finalized as most of the ITU-T development work on synchronization over packet networks is still under development (in draft status, or incomplete). The following three classifications are used as a guide

Class A2. Used for unaware networks with frequency synchronization, suitable for ITU-T G.8263 and/or ITU-T G.8261.1 PDV network limits. Used for unaware networks with frequency synchronization, based on ITU-T G.8261 Appendix VI profiles. Note that the first revision on ITU-T G.8263 is published, but additional amendments and revisions are expected to clarify items such as wander tolerance testing. Oscillator requirements are taken from Stratum 3E. Note that Microsemi (API v4) has allocated 5 ppb pk-pk for the temperature effects of the Stratum 3E oscillator over a reduced temperature range profile for ITU-T G.8263 testing (see ITU-T G.8263 Amendment 1 Appendix VI).

Class B. Used for partially aware networks (3-4 nodes) with phase synchronization, such as T-BC-P, T-TSC-P and APTSC clocks. This class is under development in ITU-T G.8273.2 and G.8273.4 drafts and will be subject to change. Also may be used for unaware aware networks with relaxed frequency synchronization requirements, based on ITU-T G.8261 Appendix VI profiles.

Class C1. Used for fully aware BC networks with phase synchronization suitable for ITU-T G.8273.2 T-BC and T-TSC. Note that the first revision of ITU-T G.8273.2 is published, but additional amendments and revisions are expected to clarify items such as wander generation (TDEV), wander generation under variable temperature and holdover. Therefore deviations (tougher requirements) from these requirements may be expected, especially related to wander generation (at 0.05 Hz) and holdover stability under variable temperature.

Class D1. Used for fully aware BC networks when combined with EEC option 1 reference chain, with phase synchronization suitable for ITU-T G.8273.2 T-BC and T-TSC. Note that the first revision of ITU-T G.8273.2 is published, but additional amendments and revisions are expected to clarify items such as wander generation (TDEV), wander generation under variable temperature and holdover. Therefore deviations (tougher requirements) from these requirements may be expected, especially related to holdover performance under variable temperature conditions without SyncE.

Oscillators For Protocol Layer Synchronization

CLASSIFICATION

CLASS B

Used for partially aware networks with phase synchronization, such as T-BC-P, T-TSC-P and APTSC clocks. Used for unaware aware networks with relaxed frequency synchronization requirements, based on ITU-T G.8261 Appendix VI profiles.

OCXOs for CLASS B