Timing synchronization for networks with radio links
Precision Timing Protocol (PTP) related functions for use in packet communications carried in part by a microwave communications link include setting of time of day values across the microwave link and providing transparent clock functions. The PTP functions may be used for synchronizing radio base stations in a cellular network. The transparent clock can bridge Ethernet switches associated with microwave stations providing the microwave communications link.
1. A method of performing timing related processing in a packet-based network communications over a microwave communications link, the method comprising:
synchronizing clocks of a first packet handling circuitry element and a second packet handling circuitry element separated by a microwave communications link, the first packet handling circuitry element being part of a first microwave station and the second packet handling circuitry element being part of a second microwave station, by determining, by a one of the first packet handling circuitry element and the second packet handling circuitry element, an expected time of day (TOD) value for a time in the future at which a periodic signal is to be commonly received or generated by the first packet handling circuitry element and the second packet handling circuitry element, and transmitting the expected TOD value over the microwave communications link to the other of the first packet handling circuitry element or the second packet handling circuitry element;
determining a time of arrival of a packet at the first packet handling circuitry element;
transmitting the time of arrival of the packet at the first packet handling circuitry element over the microwave communications link to the second packet handling circuitry element;
determining a time of departure of the packet from the second packet handling circuitry element; and
setting a correction field of the packet to a value based on at least the time of departure of the packet from the second packet handling circuitry element and the time of arrival of the packet at the first packet handling circuitry element.
2. The method of claim 1 , further comprising setting, by the other of the first packet handling circuitry or the second packet handling circuitry, a local TOD to the expected TOD value upon receipt or generation of the periodic signal.
3. The method of claim 1 , wherein setting the correction field of the packet to the value based on at least the time of departure of the packet from the second packet handling circuitry element and the time of arrival of the packet at the first packet handling circuitry element comprises setting the correction field of the packet to a value equal to a value of the correction field plus the difference between the time of departure of the packet from the second packet handling circuitry element and the time of arrival of the packet at the first packet handling circuitry element.
4. The method of claim 1 , wherein the first packet handling circuitry and the second packet handling circuitry each include a switch for routing packets.
5. The method of claim 1 , wherein the first packet handling circuitry comprises a first Ethernet switch and the second packet handling circuitry comprises a second Ethernet switch.