# ITU-T G.8273.3 (T-TC) One-Page Summary

**Title: ***Timing characteristics of Telecom Transparent Clocks (T-TC)*

*Timing characteristics of Telecom Transparent Clocks (T-TC)*

**Summary**

Clock specification for T-TC (transparent clock) for full timing support architecture, including noise tolerance, noise generation, noise transfer, phase transients

Two clock types defined, classes A and B

Class A intended for short chains (up to 10 clocks), to meet ±1.5µs overall requirement

Class B intended for long chains (up to 20 clocks), to meet ±1.5µs overall requirement

T-TCs are considered a direct replacement for T-BCs in the full timing support architecture, provided the T-TCs comprise no more than eight clocks in the overall chain (as per II.2.1 of G.8271.1)

**Status**

Current version:

plus**1st. Edition, October 2017****Amd. 1, November 2018**Download from: http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=13327

**Key Contents**

**Noise Generation:**

Parameter | Conditions | Class A | Class B |
---|---|---|---|

Max |TE| | Unfiltered, 1000s | 100ns | 70ns |

Max|TE | 0.1Hz low-pass filter,1000s | - | - |

cTE | Averaged over 1000s | 50ns | 20ns |

dTE | 0.1Hz low-pass filter, Const. temp, 1000s | 40ns | 40ns |

0.1Hz low-pass filter, Var. temp, 10000s | 40ns | 40ns | |

dTE | 0.1Hz low-pass filter, Const. temp, 1000s | 4ns | 4ns |

dTE | 0.1Hz high-pass filter, Const. temp, 1000s | 70ns | 70ns |

**Transfer Function:**

- No filtering of noise from PTP input to output
- Low-pass filtering of noise on physical layer frequency input, bandwidth between 1 and 10Hz

**Holdover:**

- No holdover provided by a T-TC

**Simplified Functional Model:**

**On this page:**