PACKET-BASED TIMING MEASUREMENT

1 . A method of determining a time of transit of a packet over a communication network, comprising:

providing a physical layer portion of a slave communication device a packet including a value indicating an approximate time of transmission of the packet by the slave communication device;

having the physical layer portion of the slave communication device insert a correction value into the packet, the correction value indicating a difference between the approximate time of transmission and an actual time of transmission of the packet by the slave communication device;

transmitting, by the physical layer portion of the slave communication device, the packet to a master communication device;

receiving, by the slave communication device, a responsive packet from the master communication device, the responsive packet including a time value indicating a time of receipt of the packet by the master communication device and an indication of the correction value; and

calculating the time of transit by the packet over the communication network using the approximate time of transmission, the indication of the correction value, and the time of receipt by the master communication device.

2 . The method of claim 1 , wherein the calculating the time of transit is performed in a higher layer of the slave communication device.

3 . The method of claim 2 , wherein the higher layer is a media access controller (MAC).

4 . The method of claim 1 , wherein the packet sent by the physical layer portion of the slave communication device comprises a Delay_Req message.

5 . The method of claim 1 , wherein the responsive packet received by the master communication device comprises a Delay_Resp message.

6 . The method of claim 1 , wherein the master and slave devices follow precision time protocol (PTP).

7 . The device of claim 1 , wherein the physical layer portion does not retain information of the actual time of transmission after transmission of the packet transmission time information.

8 . A network communication device for determining a time of transit for a packet over a communication network, comprising:

at least one port for transmitting and receiving network packets;

a higher layer configured to provide packets to a physical layer, at least some of the packets including a value indicating an approximate time of transmission of the packet by the communication device; and

the physical layer configured to insert a correction value in at least some of the packets the correction value indicating a difference between the approximate time of transmission and the actual time of transmission of the packet by the communication device, to transmit the packet over a communication network to a master communication device, to receive responsive packets from the master communication device, at least some of the responsive packets including a time value indicating a time of receipt of the packet by the master communication device and the correction value.

9 . The device of claim 8 , wherein the higher layer is a media access controller.

10 . The device of claim 8 , wherein the physical layer portion is an integrated circuit.

11 . A method for determining a time of transit for a packet over a communication network, comprising:

receiving from a media access controller (MAC) by a packet physical layer portion of a slave communication device, the packet including a value indicating an approximate time of transmission of the packet by the slave communication device;

modifying a correction field of the packet to indicate a difference between the approximate time of transmission and an actual time of transmission of the packet by the slave communication device;

transmitting the packet from the physical layer portion of the slave communication device over a communication network to a master communication device;

receiving, by the slave communication device, a responsive packet from the master communication device, the responsive packet including a time value indicating a time of receipt of the packet by the master communication device and the correction value; and

calculating the time in transit of the packet over the communication network using the approximate time of transmission, the correction value, and the time of receipt by the master communication device.

12 . The method of claim 11 , wherein the correction value is a time value measurement.

13 . The method of claim 11 , wherein the packet sent by the physical layer portion of the slave communication device comprises a Delay_Req message.

14 . The method of claim 11 , wherein the packet sent by the master communication device comprises a Delay_Resp message.

15 . The method of claim 11 , wherein the slave device physical layer portion does not retain transmission time information.

16 . The method of claim 11 , wherein the correction value is further corrected for resident time in a device on the communication network.

17 . The method of claim 11 , wherein the calculation is performed in a higher layer of the slave communication device.