Systems and methods for packet based timing offset determination using timing adjustment information

1. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave-*master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein the timing adjustment information comprises topology type information that identifies a type of topology relevant to the communications path.

2. The method of claim 1 wherein the topology type information identifies one of a set of pre-defined possible configurations.

3. The method of claim 1 wherein the topology type information identifies some or all of the communications path to be one of:

direct connection;

a link with fixed delay with constant jitter;

a link with small and fixed amount of asymmetrical offset;

a link having a protection path that is of fixed delay, small constant jitter, and small asymmetrical delay;

a topology in which each network device is a network device that makes adjustments to timing packets to reflect delay introduced by the network device;

a topology in which each intermediate network device is a network device that makes adjustments to timing packets to reflect delay introduced by the network device;

a topology in which any network devices that make adjustments to timing packets to reflect delay are connected through direct connections;

a topology formed of network devices that are managed and controlled by a common entity;

a topology in which no network device that makes adjustments to timing packets to reflect delay introduced by the network device;

a topology providing a managed service (leased line, E-line) for which specific management information is available, but control is by a separate entity;

a topology that is path performance bounded in terms of at least one of delay and jitter;

a topology for which there is no management visibility; and

a topology for which there is no bounded performance, unknown paths and unknown protection capability.

4. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

the method further comprising:

transmitting and receiving timing packets on an ongoing first basis; and

after a change in communications path to a different communications path, increasing a frequency of transmitting and receiving timing packets to speed up acquisition of delay characteristics for the different communications path.

5. The method of claim 4 further comprising detecting a change in path by performing at least one of:

receiving a notification of the change of path; and

detecting an out of bounds delay for a timing packet.

6. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

the method further comprising generating an estimate of a fractional frequency offset using the timing adjustment information and using transmit and receive times for multiple master→slave timing packets, wherein said generating an estimate comprises:

estimating a mean delay from the master device to the slave device using transmit and receive times for multiple master→slave timing packets and using the timing adjustment information; and

generating an estimate of the fractional frequency offset using the mean delay.

7. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein obtaining the timing adjustment information comprises at least one of:

employing DCC (Data Communication Channel) in SONET/SDH to carry the information;

employing GCC (General Communication Channel) in OTN to carry the information;

employing management packets in Ethernet; and

employing PTPv2 over UDP Signalling TLV (Type-Length-Value) in IP networks.

8. A network device comprising:

a timing protocol module configured to transmit a slave→master timing packet and to receive a master→slave timing packet; the timing protocol module further configured to receive a topology update pertaining to at least part of a communications path over which the slave→master timing packet was transmitted and the master→slave timing packet was received indicating a change to the communications;

a timing adjustment module further configured to perform at least one of:

a) generate an estimate of a timing offset using the topology update and using transmit and receive times for the slave→master timing packet and the master→slave timing packet; and

b) generate an estimate of a fractional frequency offset using the topology update and using transmit and receive times for multiple master→slave timing packets;

wherein the network device is further configured to increase a speed of transmission of slave→master timing packets and receipt of a master→slave timing packets upon receipt of the topology update to increase a speed of acquisition of delay characteristics.

9. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein the timing adjustment information is representative of a change in conditions in the network, and wherein the timing adjustment information representative of the change in conditions in the network is indicative of a change in topology.

10. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein the timing adjustment information is representative of a change in conditions in the network, and wherein the offset is a timing offset, and wherein generating the estimate of the timing offset comprises:

updating a mean master→slave delay based on the transmit and receive times for the master→slave timing packets and the timing adjustment information by applying a correction to the mean master→slave delay to account for the change in conditions in the network;

updating a mean slave→master delay based on the transmit and receive times for the slave→master timing packets and the timing adjustment information by applying a correction to the mean master→slave delay to account for the change in conditions in the network; and

determining the timing offset according to:

timing offset=(mean master→slave delay mean+slave→master delay)/2; and

wherein the timing adjustment information representative of the change in conditions in the network is indicative of a change in topology.

11. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein the offset is a timing offset and wherein generating an estimate of the timing offset comprises:

updating a mean master→slave delay based on the transmit and receive times for the master→slave timing packets and the timing adjustment information;

updating a mean slave→master delay based on the transmit and receive times for slave→master timing packets and the timing adjustment information; and

determining the timing offset according to:

timing offset=(mean master→slave delay+mean slave→master delay)/2; and

wherein at least one of:

updating a mean master→slave delay based on the transmit and receive times for the master→slave timing packets and the timing adjustment information comprises employing a weighted averaging approach in which each master→slave delay is given a weight that is representative of the reliability of the accuracy of the delay;

updating a mean slave→master delay based on the transmit and receive times for the slave→master timing packets and the timing adjustment information comprises employing a weighted averaging approach in which each slave→master delay is given a weight that is representative of the reliability of the accuracy of the delay.

12. A method in a slave device to estimate an offset between the slave device and a master device, the method comprising:

receiving a master→slave timing packet;

obtaining timing adjustment information pertaining to at least part of a communications path between the slave device and the master device, at least some of the timing adjustment information obtained otherwise than from any received master→slave timing packet, transmit and receive times of the any received master→slave timing packet, and transmit and receive times of any transmitted slave→master timing packet;

generating an estimate of the offset using the timing adjustment information and using the transmit and receive times for the master→slave timing packet;

wherein generating the estimate comprises determining a mean delay for timing packets based on the transmit and receive times for the timing packets, and the timing adjustment information comprises employing a weighted averaging approach in which each master→slave delay is given a weight that is representative of the reliability of the accuracy of the delay.