G.811

G.811 Timing characteristics of primary reference clocks is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T). It specifies requirements for primary reference clock devices in synchronization networks. It discusses timing requirements for connecting national telecommunications networks.{{cite book |last1=Smith |first1=David R. |title=Digital Transmission Systems |date=2003 |publisher=Springer Science & Business Media |isbn=978-1-4020-7587-2 |page=652 |url=https://books.google.com/books?id=4IASeihofskC&dq=%22G.811%22&pg=PA652 |language=en}} Primary reference clocks need to be highly accurate and are often based on caesium atomic clocks that meet the standards of G.811.{{cite book |last1=Manning |first1=Trevor |title=Microwave Radio Transmission Design Guide |date=2009 |publisher=Artech House |isbn=978-1-59693-457-3 |page=88 |url=https://books.google.com/books?id=15wiVQwLMNwC&dq=%22G.811%22+&pg=PA88 |language=en}}