Frame transmitting apparatus, frame receiving apparatus, and frame transmission/reception system and method
View Patent ↗To enable more precise synchronization of distributed clocks, before a high-level frame is converted to a low-level frame for transmission over a communication network, if the high-level frame includes a certain type of message, it is flagged. The flag is detected during the conversion process, and the time of detection is stored as a transmission timestamp. When a low-level frame is received from the network, it is immediately timestamped with the time of reception. The timestamped frame is then converted to a high-level frame, and if the high-level frame includes the certain type of message, the timestamp is stored as a reception timestamp.
1. A frame receiving apparatus, comprising:
a processor that performs processes of:
receiving a low-level frame belonging to a physical layer from a communication network;
generating a timestamp representing a time at which the low-level frame is received and adding the timestamp to the low-level frame, thereby generating a timestamped frame;
removing the timestamp from the timestamped frame, thereby holding the removed timestamp;
converting a frame obtained by removing the timestamp from the timestamped frame, to a high-level frame belonging to an upper layer; and
restoring the removed timestamp to the high-level frame; and
a storing unit for selectively storing the time represented by the timestamp, depending on content of the high-level frame.
2. The frame receiving apparatus of claim 1 , wherein the storing unit removes the timestamp from the high-level frame.
3. The frame receiving apparatus of claim 1 , wherein the storing unit stores the time represented by the timestamp when the high-level frame includes a Sync message or a DelayReq message.
4. A frame transmitting apparatus comprising:
a processor that performs processes of:
selectively flagging high-level frames, depending on content of the high-level frames;
removing flags from the flagged high-level frames respectively, thereby holding the removed flags;
converting each frame obtained by removing the flag from the flagged high-level frame to a low-level frame belonging to a physical layer;
restoring the removed flag to the low-level frame, thereby generating a flagged low-level frame;
transmitting the flagged low-level frame over a communication network; and
determining, during conversion of the high-level frame to the low-level frame, whether the high-level frame was flagged; and
a storing unit for storing a time of detection that the high-level frame was flagged as a transmission time.
5. The frame transmitting apparatus of claim 4 , wherein the processor performs a process of flagging the high-level frame if the high-level frame includes a Sync message or a DelayReq message.
6. A frame transmission and reception system including frame transmitting apparatus and frame receiving apparatus for transmitting and receiving frames over a communication network, wherein:
the frame transmitting apparatus comprises
a first processor that performs processes of:
selectively flagging first high-level frames belonging to an upper layer, depending on content of the high-level frames,
removing flags from the flagged first high-level frames respectively, thereby holding the removed flags,
converting each frame obtained by removing a flag from a flagged first high-level frame to a low-level frame belonging to a physical layer,
restoring the removed flag to the low-level frame, thereby generating a flagged low-level frame,
transmitting the flagged low-level frame over the communication network, and
determining, during conversion of the first high-level frame to the low-level frame, whether the first high-level frame was flagged, and
a first storing unit for storing a time of detection that the first high-level frame was flagged as a transmission time; and
the frame receiving apparatus comprises
a second processor that performs processes of:
receiving the low-level frame from the communication network,
generating a timestamp representing a time at which the low-level frame is received and adding the timestamp to the low-level frame, thereby generating a timestamped frame,
removing the timestamp from the timestamped frame, thereby holding the removed timestamp,
converting a frame obtained by removing the timestamp from the timestamped frame, to a second high-level frame belonging to the upper layer, and
restoring the removed timestamp to the second high-level frame, and
a second storing unit for selectively storing the time represented by the timestamp, depending on content of the second high-level frame.
7. The frame transmission and reception system of claim 6 , wherein the second storing unit removes the timestamp from the second high-level frame.
8. The frame transmission and reception system of claim 6 , wherein the second storing unit stores the time represented by the timestamp if the second high-level frame includes a Sync message or a DelayReq message.
9. The frame transmission and reception system of claim 6 , wherein the second processor performs a process of flagging the second high-level frame if the high-level frame includes a Sync message or a DelayReq message.
10. The frame transmission and reception system of claim 6 , wherein the first processor and the second processor perform security processing.
11. A method of transmitting frames over a communication network, comprising:
selectively flagging high-level frames belonging to an upper layer, depending on content of the high-level frames;
removing flags from the flagged high-level frames respectively, thereby holding the removed flags,
converting each frame obtained by removing the flag from the flagged high-level frame to a low-level frame belonging to a physical layer;
restoring the removed flag to the low-level frame, thereby generating a flagged low-level frame,
transmitting the flagged low-level frame over the communication network;
determining, during conversion of the first high-level frame to the low-level frame, whether the first high-level frame was flagged;
storing a time of detection that the first high-level frame was flagged as a transmission time;
receiving the low-level frame from the communication network;
generating a timestamp representing a time at which the low-level frame is received and adding the timestamp to the low-level frame, thereby generating a timestamped frame;
removing the timestamp from the timestamped frame, thereby holding the removed timestamp;
converting a frame obtained by removing the timestamp from the timestamped frame, to a second high-level frame belonging to the upper layer; and
restoring the removed timestamp to the second high-level frame, and
selectively storing the time represented by the timestamp, depending on content of the second high-level frame.
12. The method of claim 11 , wherein selectively storing the time represented by the timestamp further comprises removing the timestamp from the second received high-level frame.
13. The method of claim 11 , wherein the time represented by the timestamp is stored if the second high-level frame includes a Sync message or a DelayReq message.
14. The method of claim 11 , wherein the high-level frame is flagged if the second high-level frame includes a Sync message or a DelayReq message.