Method and device for resident time calculation and synchronization

1. A method in a communications network comprising a communications link connecting a first device to a second device, wherein the communications link comprises an upper layer having a variable delay and a lower layer having a constant delay, wherein the first device comprises a first clock and the second device comprises a second clock, the method comprising:

synchronizing the first clock via the lower layer of the communications link with the second clock; and

determining, at the second device, a residence time for a fifth message when transmitted from the first device to the second device via the upper layer of the communications link,

wherein the first device further comprises a third clock and the second device comprises a fourth clock, wherein the third clock is a replica of the fourth clock, and

wherein the determining, at the second device, the residence time for the fifth message when transmitted from the first device to the second device via the upper layer of the communications link further comprises:

determining at the first device, an eleventh time stamp using the third clock for the transmission of the fifth message from the first device to the second device;

determining, at the second device, a twelfth time stamp using the fourth clock, which twelfth time stamp is associated with the receipt of the fifth message at the second device; and

determining, at the second device, a second difference between the twelfth time stamp and the eleventh time stamp; and

wherein the fifth message further comprises the eleventh time stamp.

2. The method according to claim 1 , wherein the determining, at the second device, the residence time for the fifth message when transmitted from the first device to the second device via the upper layer of the communications link further comprises:

determining, at the first device, a ninth time stamp using the first clock for the transmission of the fifth message from the first device to the second device;

transmitting the fifth message comprising the ninth time stamp from the first device to the second device via the upper layer of the communications link;

determining, at the second device, a tenth time stamp using the second clock, which tenth time stamp is associated with receipt of the fifth message at the second device; and

determining, at the second device, a first difference between the tenth time stamp and the ninth time stamp.

3. The method according to claim 2 , further comprising:

selecting at the second device, the first difference as the residence time; and

selecting at the second device, the ninth time stamp as an ingress time stamp associated with the fifth message in the communications link.

4. The method according to claim 1 , wherein the first device further comprises a third clock and the second device comprises a fourth clock, and wherein the method further comprises:

synchronizing the third clock via the lower layer of the communications link with the fourth clock.

5. The method according to claim 1 , wherein the communications link is a microwave radio link.

6. A communications network comprising:

a communications link connecting a first device to a second device, wherein the communications link comprises an upper layer having a variable delay and a lower layer having a constant delay, wherein the first device comprises a first clock and the second device comprises a second clock,

wherein the communications network is configured to synchronize the first clock via the lower layer of the communications link with the second clock; and

wherein the communications network is configured to determine, at the second device, a residence time for a fifth message when transmitted from the first device to the second device via the upper layer of the communications link,

wherein the first device further comprises a third clock and the second device comprises a fourth clock, wherein the third clock is a replica of the fourth clock,

wherein the first device is further configured to determine an eleventh time stamp using the third clock for the transmission of the fifth message from the first device to the second device; and

wherein the second device is further configured to:

determine a twelfth time stamp using the fourth clock, which twelfth time stamp is associated with the receipt of the fifth message at the second device; and to

determine a second difference between the twelfth time stamp and the eleventh time stamp; and

wherein the fifth message further comprises the eleventh time stamp.

7. The communications network according to claim 6 ,

wherein the first device is further configured to:

determine, a ninth time stamp using the first clock for the transmission of the fifth message from the first device to the second device; and to

transmit the fifth message comprising the ninth time stamp from the first device to the second device via the upper layer of the communications link; and

wherein the second device is further configured to:

determine a tenth time stamp using the second clock, which tenth time stamp is associated with receipt of the fifth message at the second device; and to

determine a first difference between the tenth time stamp and the ninth time stamp.

8. The communications network according to claim 7 , wherein the second device is further configured to:

select the first difference as the residence time; and to

select the ninth time stamp as an ingress time stamp associated with the fifth message in the communications link.

9. The communications network according to claim 6 , wherein the first device is further configured to synchronize the third clock via the lower layer of the communications link with the fourth clock.

10. The communications network according to claim 6 , wherein the communications link is a microwave radio link.

11. A method in a second device connected to a first device via a communications link in a communications network, wherein the communications link comprises an upper layer having a variable delay and a lower layer having a constant delay, wherein the second device comprises a second clock, the method comprising:

determining a residence time for a fifth message when transmitted from the first device to the second device via the upper layer of the communications link,

wherein the first device further comprises a third clock and the second device comprises a fourth clock, wherein the third clock is a replica of the fourth clock, and wherein the method further comprises:

determining a twelfth time stamp using the fourth clock, which twelfth time stamp is associated with the receipt of the fifth message at the second device; and

determining a second difference between the twelfth time stamp and an eleventh time stamp; and

wherein the fifth message further comprises the eleventh time stamp.

12. The method according to claim 11 , further comprising:

receiving a fifth message comprising a ninth time stamp from the first device via the upper layer of the communications link, which ninth time stamp is associated with transmission of the fifth message from the first device;

determining a tenth time stamp using the second clock, which tenth time stamp is associated with receipt of the fifth message at the second device; and

determining, at the second device, a first difference between the tenth time stamp and the ninth time stamp.

13. A method in a second device connected to a first device via a communications link in a communications network, wherein the communications link comprises an upper layer having a variable delay and a lower layer having a constant delay, wherein the second device comprises a second clock, the method comprising:

determining a residence time for a fifth message when transmitted from the first device to the second device via the upper layer of the communications link;

receiving a first message from the first device with the constant delay in the lower layer of the communications link;

determining a second time stamp using the second clock, which second time stamp is associated with receipt of the first message at the second device;

determining a third time stamp using the second clock for a transmission of a second message from the second device to the first device;

transmitting the second message to the first device with the constant delay in the lower layer of the communications link;

receiving a first time stamp and a fourth time stamp from the first device, which first time stamp is associated with transmission of a first message from the first device and which fourth time stamp is associated with receipt of the second message at the first device;

synchronizing the second clock in the second device to the first clock in the first device using the first time stamp, the second time stamp, the third time stamp and the fourth time stamp;

determining a fifth time stamp using the fourth clock for a transmission of a third message from the second device to the first device;

transmitting the third message to the first device with the constant delay in the lower layer of the communications link;

receiving a fourth message from the first device with the constant delay in the lower layer of the communications link;

determining an eighth time stamp using the fourth clock, which eighth time stamp is associated with receipt of the fourth message; and

transmitting the fifth time stamp and the eighth time stamp to the first device.