Network distributed packet-based synchronization

1. A method of providing a transparent clock path through a non-precision time protocol network, the method comprising:

synchronizing a clock of a first Ethernet line card and a clock of a second Ethernet line card separated by a non-precision time protocol network, the first Ethernet line card being part of a first network device of the non-precision time protocol network and the second Ethernet line card being part of a second network device of the non-precision time protocol network, the first Ethernet line card and the second Ethernet line card each being connected to a precision time protocol network, the first Ethernet line card including a first PHY and the second Ethernet line card including a second PHY;

determining, by the first PHY, a time of arrival of a packet from the precision time protocol network at the first Ethernet line card;

inserting an indication of the time of arrival of the packet at the first Ethernet line card into a reserved field of the packet;

transmitting the packet over the non-precision time protocol network from the first network device to the second network device;

determining, by the second PHY, a time of departure of the packet from the second Ethernet line card to the precision time protocol network; and

adding a value equal to the determined time of departure of the packet from the second Ethernet line card minus the determined time of arrival of the packet at the first Ethernet line card to a value of a correction field of the packet.

2. The method of claim 1 , wherein the indication of the time of arrival includes less resolution than allowed for by the reserved field of the packet.

3. The method of claim 2 , wherein the indication of the time of arrival omits information with a resolution greater than an expected delay of transmission between the first Ethernet line card and the second Ethernet line card.

4. The method of claim 1 , wherein the first network device includes at least the first Ethernet line card, a system card, and a specialized medium line card, with the specialized medium line card connected to another network device of the non-precision time protocol network.

5. The method of claim 4 , wherein the other network device is the second network device.

6. The method of claim 4 , wherein the non-precision time protocol network is a passive optical network.

7. The method of claim 1 , wherein the clock of the first Ethernet line card and the clock of the second Ethernet line card are each synchronized to each other via a communication protocol of the non-precision time protocol network.

8. The method of claim 7 , wherein each of the first network device and the second network device comprise respective specialized medium line cards, wherein said transmitting the packet over the non-precision time protocol network from the first network device to the second network device comprises transmitting the packet from the respective specialized medium line card of the first network device to the respective specialized medium line card of the second network device.

9. A system arranged to provide a transparent clock path through a non-precision time protocol network, the system comprising:

a first network device of the non-precision time protocol network, said first network device of the non-precision time protocol network comprising a first Ethernet line card and having an associated first clock, said first Ethernet line card in communication with a device of a precision time protocol domain; and

a second network device of the non-precision time protocol network, said second network device of the non-precision time protocol network comprising a second Ethernet line card and having an associated second clock, said second network device associated clock different from said first network device associated clock and synchronized with said first network device associated clock, said first network device in communication with said second network device over the non-precision time protocol network,

said first network device of the non-precision time protocol network arranged to:

determine a time of arrival of a packet, at the first Ethernet line card, from the device of the precision time protocol network;

insert an indication of the time of arrival of the packet at the first Ethernet line card into a reserved field of the packet; and

transmit the packet over the non-precision time protocol network to the second network device of the non-precision time protocol network,

said second network device of the non-precision time protocol network arranged to:

determine a time of departure of the packet from the second Ethernet line card to at least one additional device of the precision time protocol network; and

add a value equal to the determined time of departure of the packet from the second Ethernet line card minus the determined time of arrival of the packet at the first Ethernet line card to a value of a correction field of the packet.

10. The system according to claim 9 , wherein said first Ethernet line card comprises a respective PHY, said first Ethernet line card PHY arranged to determine said time of arrival of the packet.

11. The system according to claim 10 , wherein said second Ethernet line card comprises a respective PHY, said second Ethernet line card PHY arranged to determine said time of departure of the packet.

12. The system according to claim 9 , wherein said synchronization of said second network device associated clock with said first network device associated clock is responsive to a communication protocol of the non-precision time protocol network.

13. The system according to claim 9 , wherein said first network device of the non-precision time protocol network further comprises a system card and a specialized medium line card, said specialized medium line card connected to another network device of the non-precision time protocol network.

14. The system according to claim 13 , wherein the other network device is the second network device.

15. The system according to claim 9 , wherein the non-precision time protocol network is a passive optical network.

16. The system according to claim 9 , wherein each of the first network device and the second network device of the non-precision time protocol network comprise respective specialized medium line cards, wherein said transmitting the packet over the non-precision time protocol network from the first network device to the second network device comprises transmitting the packet from the respective specialized medium line card of the first network device to the respective specialized medium line card of the second network device.