Method for Synchronizing Clocks in a Communication Network

A method for synchronizing clocks comprising:

• (a) a master element of a network sending a first sync message to a first slave element, the first sync message having information identifying a first time, the first time being a time of a clock of the master element at which the first sync message was sent by the master element;
• (b) the first slave element of the network receiving the first sync message at a second time, the second time being a time of a clock of the first slave element at which the first sync message was received by the first slave element;
• (c) in response to receiving the first sync message, the first slave element sending a first line delay request message to the master element at a third time, the third time being a time of the clock of the first slave element at which the first line delay request message is sent to the master element;
• (d) the master element receiving the first line delay request message at a fourth time, the fourth time being a time of the clock of the master element at which the first line delay request message is received by the master element;
• (e) in response to receiving the first line delay request message, the master element sending a first line delay response message having information identifying the fourth time to the slave element;
• and
• (f) the slave element receiving the first line delay response message such that the slave element knows the first time, the second time, the third time, and the fourth time;
• and
• (g) the slave element calculating a line delay based on the first, second, third and fourth times.

A communication network comprising:

• a first network element communicatively connected to a second network element, the first network element having a first clock, the second network element having a second clock;
• the first network element sending a plurality of first messages to the second network element, each of the first messages having a first counter identifying a time of the first clock at which the first message was sent by the first network element, each of the first messages being a synchronization message to synchronize the first clock with the second clock of the second network element;
• the second network element receiving each of the first messages;
• in response to receiving each of the first messages, the second network element recording a time of the second clock corresponding to when the first message was received by the second network element as a first message received time value;
• the second network element saving the first counter of the first message for each of the received first messages;
• the second network element sending a plurality of second messages to the first network element, each of the second messages identifying a second counter to identify a time of the second clock at which the second network element sent the second message;
• the second network element saving the second counter for each of the second messages;
• the first network element receiving each of the second messages;
• in response to the second messages, the first network element sending a plurality of third messages, each of the third messages sent in response to a respective one of the second messages received by the first network element, each of the third messages having a third value identifying a value of the first clock at a time the first network element received the second message;
• the second network element receiving each of the third messages from the first network element;
• the second network element saving the third value of the third message for each of the received third messages;
• the second network element applying a filtering method to filter data from the first messages and third messages for determining a line delay affecting communications between the first and second network elements, the filtering method comprising:
• identifying data from first messages received from the first network element that are from first messages having a transmission delay in passing from the first network element to the second network element in which a difference between the first counter and the first message received time value is at or below a first threshold to filter the first messages so that a filtered subset of the first messages is identified and data from the filtered subset of first messages is identified to determine the line delay, and
• identifying data from third messages received from the first network element that are from third messages that respond to second messages that have a transmission delay in passing from the second network element to the first network element in which a difference between the second counter and the third value is at or below a second threshold so that a filtered subset of the third messages is identified and data from the filtered subset of third messages is identified to determine the line delay;
• the second network element determining a line delay utilizing data from the filtered subset of first messages and the filtered subset of third messages;
• and
• the second network element applying the determined line delay to time information communicated by the first network element to synchronize the second clock with the first clock.

A method for synchronizing clocks in a communication network, wherein a first clock of a first network element is used for synchronizing at least one second clock of one or more second network elements, comprising:

• the first network element sending a plurality of first messages to one of the second network elements, each of the first messages having a first counter identifying a time of the first clock at which the first message was sent by the first network element, each of the first messages being a synchronization message to synchronize the first clock with the second clock of the second network element;
• the second network element receiving each of the first messages;
• in response to receiving each of the first messages, the second network element recording a time of the second clock corresponding to when the first message was received by the second network element as a first message received time value;
• the second network element saving the first counter of the first message for each of the received first messages;
• the second network element sending a plurality of second messages to the first network element, each of the second messages identifying a second counter to identify a time of the second clock at which the second network element sent the second message;
• the second network element saving the second counter for each of the second messages;
• the first network element receiving each of the second messages;
• in response to the second messages, the first network element sending a plurality of third messages, each of the third messages sent in response to a respective one of the second messages received by the first network element, each of the third messages having a third value identifying a value of the first clock at a time the first network element received the second message;
• the second network element receiving each of the third messages from the first network element;
• the second network element saving the third value of the third message for each of the received third messages;
• applying a filtering method to filter data from the first messages and third messages for determining a line delay affecting communications between the first and second network elements, the filtering method comprising:
• identifying data from first messages received from the first network element that are from first messages having a transmission delay in passing from the first network element to the second network element in which a difference between the first counter and the first message received time value is at or below a first threshold to filter the first messages so that a filtered subset of the first messages is identified and data from the filtered subset of first messages is identified to determine the line delay, and
• identifying data from third messages received from the first network element that are from third messages that respond to second messages that have a transmission delay in passing from the second network element to the first network element in which a difference between the second counter and the third value is at or below a second threshold so that a filtered subset of the third messages is identified and data from the filtered subset of third messages is identified to determine the line delay;
• the second network element determining a line delay utilizing data from the filtered subset of first messages and the filtered subset of third messages;
• and
• the second network element applying the determined line delay to time information communicated by the first network element to synchronize the second clock with the first clock.