Method and apparatus for precision time distribution in telecommunication networks

A time-transfer apparatus for synchronizing a network, the network including a plurality of intermediate nodes serially bridged across an incoming transmission path and an outgoing transmission path, and including one loop node connected across the incoming and outgoing transmission paths, the time-transfer apparatus comprising:

• (1) means for transmitting a first trigger signal along the outgoing transmission path;
• (2) means for returning a second trigger signal on the incoming transmission path, the second trigger signal having time information appended to it, on arrival of the first trigger signal at the loop node;
• (a) means for detecting the first trigger signal on the outgoing transmission path and the second trigger signal on the incoming transmission path;
• (b) means for counting the elapsed time between the detection of the first trigger signal on the outgoing transmission path and detection of the second trigger signal on the incoming transmission path;
• (c) means for adjusting the elapsed time for two way travel time and for processing delays, to produce adjusted time information representative of the one way travel time delay between the intermediate node and the loop node;
• (d) means for latching the time information appended to the second trigger signal returning on the incoming transmission path;
• (e) means for adding the latched time information to the adjusted time information to produce synchronized tie information;
• and
• (f) real time clock register means for storing the synchronized time information.

A time transfer apparatus for a network element in a network having a plurality of network elements connected by a bi-directional transmission path, the bi-directional transmission path having an incoming transmission path and an outgoing transmission path, one of the plurality of network elements including means for returning a second trigger signal on the incoming transmission path with appended time information and the network including means for sending a first trigger signal along the outgoing transmission path, the time transfer apparatus comprising:

• a real time clock register;
• first detector means connected to the outgoing transmission path and responsive to the first trigger signal for generating a first detection signal;
• second detector means connected to the incoming transmission path and responsive to the second trigger signal on the incoming transmission path for generating a second detection signal;
• counter means responsive to the first and second detection signals for detecting elapsed time between detection of the first and second trigger signals by the first and second detector means;
• means connected to the incoming transmission path and responsive to the second detector means for latching the time information appending to the second trigger signal;
• means connected to the counter means for adjusting the elapsed time detected by the counter means for two-way travel time and processing delay;
• and
• means for adding the latched time information to the elapsed time information to create absolute time synchronized information and for storing the absolute time synchronized information in the real time clock register.

A time transfer apparatus for a network element in a network having a plurality of nodes, in which the network element is connected to the network by incoming and outgoing transmission paths, the network including means for sending a first trigger signal along the outgoing transmission path, the time transfer apparatus comprising:

• a real time clock register capable of containing time information;
• detector means connected to the incoming transmission path and responsive to the first trigger signal for generating a detection signal;
• return circuit means for returning a second trigger signal on the outgoing transmission path upon detection of the first trigger signal;
• and
• sender means connected to the real time clock register and responsive to the detection signal for injecting the time information into the outgoing transmission path appended to the second trigger signal.