Packet network clock distribution by line timing synchronisation with clock accuracy packets and selection amongst incoming timing signals

摘要

In a packet network 400 (eg Ethernet) line timing signals 419 are injected on to the communication lines. At the receivers 402-5 the clock information is extracted 441. For node with multiple incoming port 404 selection is made amongst the clock signals to feed the local timing engine 446 and a derived clock signal output 454/456. In other nodes 405 one or more of these derived signal 456 may be received and selected amongst 435 to drive the local timing engine 447. The packet data streams may include synchronisation status packets that identify the accuracy level of the reference clock source 411. Receivers can select amongst the available incoming clocks by comparing pairs of clocks in turn. Nodes may redistribute the derived clock signals as line timing over output ports. The system may be used to distribute clocks from central offices to base stations in wireless telephone networks. The base stations may use the clocks to generate air interface clocks.