Inband timestamping
Embodiments are directed to timing synchronization between network nodes, such as, for example, based upon IEEE 1588. Example embodiments provide for a node in a IEEE 1588 message exchange to obtain the T3 timestamp without using its host interface to access the physical layer. Methods and systems include aspects of determining an egress timestamp corresponding to a time at which a first packet is transmitted from a physical interface of a first network entity on to a network media, storing the egress timestamp in a memory associated with the physical interface, receiving a second packet at the physical interface, retrieving the egress timestamp from the memory based upon the second packet, and updating the second packet with the retrieved egress timestamp. Embodiments may further include providing the updated second packet for protocol processing in the first network entity, or transmitting the updated second packet from the physical interface on to a network media.
1. A method, comprising:
determining an egress timestamp corresponding to a time at which a first packet is transmitted from a physical interface of a first network entity;
storing the egress timestamp and an identifier of the first packet in a memory associated with the physical interface;
receiving at the physical interface a second packet from a second network entity;
retrieving the egress timestamp from the memory based upon the received second packet;
updating the second packet with the retrieved egress timestamp; and
providing the updated second packet for protocol processing in the first network entity.
2. The method of claim 1 , wherein the second packet is transmitted by the second network entity in response to receiving the first packet.
3. The method of claim 1 , wherein the retrieving comprises:
determining an identifier for the received second packet; and
accessing the memory using the determined identifier.
4. The method of claim 3 , wherein the determining an identifier comprises:
combining a plurality of header fields from the received second packet to form the identifier.
5. The method of claim 1 , wherein the updating comprises:
writing the retrieved egress timestamp in a reserved field in a header of the received second packet.
6. The method of claim 5 , wherein the updating further comprises:
calculating a checksum after writing the retrieved egress timestamp; and
writing the checksum in the received second packet.
7. The method of claim 1 , wherein the memory and the physical interface are on a network physical layer chip.
8. The method of claim 1 , wherein the retrieving and the updating are performed in a network physical layer chip.
9. The method of claim 1 , wherein the providing comprises:
sending the updated second packet from a network physical layer to a higher layer in response to a request over a host interface to the physical interface.
10. The method of claim 1 , further comprising:
obtaining the egress timestamp and an ingress timestamp from the provided second packet; and
determining a clock correction for the first network entity based at least upon the obtained egress and ingress timestamps.
11. The method of claim 10 , wherein the ingress timestamp corresponds to a time at which the first packet is received at the second network entity.
12. The method of claim 1 , wherein the first and second packets are IEEE 1588 packets, and wherein the egress timestamp corresponds to an egress time of a delay request packet.
13. A method, comprising:
determining an egress timestamp corresponding to a time at which a first packet is transmitted from a physical interface of a first network entity;
storing the egress timestamp in a memory associated with the physical interface;
receiving a second packet at the physical interface;
retrieving the egress timestamp from the memory based upon the received second packet;
updating the second packet with the retrieved egress timestamp; and
transmitting the updated second packet from the physical interface on to a network media.
14. The method of claim 13 , wherein the retrieving and the updating are performed in a network physical layer chip.
15. The method of claim 13 , wherein the retrieving comprises:
determining an identifier for the received second packet; and
accessing the memory using the determined identifier.
16. A system, comprising:
(a) a network physical layer (PHY) configured to be accessed by a central processing unit (CPU) using a host interface, the network PHY comprising:
a physical interface configured to transmit packets to and receive packets from a network medium; and
a timestamp memory,
and the network PHY being further configured to:
determine an egress timestamp corresponding to a time at which a first packet is transmitted from the physical interface to the network medium;
store the egress timestamp in the timestamp memory;
receive at the physical interface a second packet from a second network entity;
retrieve the egress timestamp from the timestamp memory based upon the received second packet;
update the second packet with the retrieved egress timestamp; and
provide the updated second packet for protocol processing on the CPU.
17. The system of claim 16 , further comprising:
(a) a system memory coupled to the CPU; and
(b) a protocol processing module configured to execute on the CPU, and further configured to:
receive the second packet from the network PHY; and
obtain the egress timestamp and one or more other timestamps from the second packet.
18. The system of claim 17 , wherein the protocol processing module is further configured to:
obtain the egress timestamp and an ingress timestamp from the provided second packet; and
determine a clock correction for the first network entity based at least upon the obtained egress and ingress timestamps.
19. The system of claim 18 , wherein the ingress timestamp corresponds to a time the first packet is received at the second network entity.
20. The system of claim 16 , wherein the second packet is transmitted by the second network entity in response to the first packet.