MONITORING CLOCK ACCURACY IN ASYNCHRONOUS TRAFFIC ENVIRONMENTS
Various exemplary embodiments relate to a method and related network system including one or more of the following: a first network device comprising a first clock; and a second network device comprising a second clock, wherein the first network device and the second network device are configured to employ a frequency distribution scheme to attempt to set the second clock to operate at the same frequency as the first clock; the first network device is configured to generate and transmit a synchronous stream of timing packets to the second network device, wherein the timing packets are periodically transmitted based on the first clock; and the second network device is configured to receive the synchronous stream of timing packets and determine, based on comparing the synchronous stream of timing packets to the second clock, whether the second clock is out of sync with the first clock.
1 . A network device for enabling downstream monitoring clock accuracy comprising:
a network interface configured to communicate with a downstream device; and
a processor configured to:
communicate with the downstream device via the network interface according to a frequency distribution scheme to distribute a local clock frequency to the downstream device,
periodically generate timing packets based on the local clock frequency, and
transmit the generated timing packets to the downstream device via the network interface as a first synchronous stream.
2 . The network device of claim 1 , wherein, in periodically generating the timing packets based on the local clock frequency, the processor is configured to:
count clock pulses generated according to the local clock frequency; and
generate a timing packet when a number of counted clock pulses exceeds a predetermined threshold.
3 . The network device of claim 1 , wherein the processor is further configured to:
receive an asynchronous stream of data packets; and
forward the asynchronous stream of data packets to the downstream node via the network interface.
4 . The network device of claim 1 , wherein the processor is further configured to:
communicate with an upstream device according to the frequency distribution scheme to establish the local clock frequency;
receive timing packets as part of a second synchronous stream;
verify the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency.
5 . The network device of claim 4 , wherein the processor is further configured to:
initiate recovery for the local clock frequency when the processor determines, as a result of verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency, that the local clock frequency is not sufficiently accurate.
6 . The network device of claim 4 , wherein, in verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency, the processor is configured to:
count a number of timing packets received via the second synchronous stream within a window;
estimate a number of timing packets expected to be received via the second synchronous stream within the window based on the local clock frequency; and
compare the counted number to the estimated number.
7 . The network device of claim 4 , wherein, in verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency, the processor is configured to:
add data into a buffer based on the second synchronous stream,
remove data from the buffer based on the local clock frequency, and
monitor the buffer for at least one of overrun and underrun.
8 . A method performed by a network device for enabling downstream monitoring clock accuracy comprising:
communicating, by the network device, with the downstream device according to a frequency distribution scheme to distribute a local clock frequency to the downstream device;
periodically generating timing packets based on the local clock frequency; and
transmitting the generated timing packets to the downstream device as a first synchronous stream.
9 . The method of claim 8 , wherein periodically generating the timing packets based on the local clock frequency comprises:
counting clock pulses generated according to the local clock frequency; and
generating a timing packet when a number of counted clock pulses exceeds a predetermined threshold.
10 . The method of claim 8 , further comprising:
receiving an asynchronous stream of data packets; and
forwarding the asynchronous stream of data packets to the downstream node via the network interface.
11 . The method of claim 8 , further comprising:
communicating with an upstream device according to the frequency distribution scheme to establish the local clock frequency;
receiving timing packets as part of a second synchronous stream;
verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency.
12 . The method of claim 11 , further comprising:
initiating recovery for the local clock frequency when the result of verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency indicates that the local clock frequency is not sufficiently accurate.
13 . The method of claim 11 , wherein verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency comprises:
counting a number of timing packets received via the second synchronous stream within a window;
estimating a number of timing packets expected to be received via the second synchronous stream within the window based on the local clock frequency; and
comparing the counted number to the estimated number.
14 . The method of claim 11 , wherein verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency comprises:
adding data into a buffer based on the second synchronous stream,
removing data from the buffer based on the local clock frequency, and
monitoring the buffer for at least one of overrun and underrun.
15 . A non-transitory machine-readable storage medium encoded with instructions for execution by a network device for enabling downstream monitoring clock accuracy comprising:
instructions for communicating, by the network device, with the downstream device according to a frequency distribution scheme to distribute a local clock frequency to the downstream device;
instructions for periodically generating timing packets based on the local clock frequency; and
instructions for transmitting the generated timing packets to the downstream device as a first synchronous stream.
16 . The non-transitory machine-readable storage medium of claim 15 , wherein the instructions for periodically generating the timing packets based on the local clock frequency comprise:
instructions for counting clock pulses generated according to the local clock frequency; and
instructions for generating a timing packet when a number of counted clock pulses exceeds a predetermined threshold.
17 . The non-transitory machine-readable storage medium of claim 15 , further comprising:
instructions for communicating with an upstream device according to the frequency distribution scheme to establish the local clock frequency;
instructions for receiving timing packets as part of a second synchronous stream;
instructions for verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency.
18 . The non-transitory machine-readable storage medium of claim 17 , further comprising:
instructions for initiating recovery for the local clock frequency when the result of executing the instructions for verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency indicates that the local clock frequency is not sufficiently accurate.
19 . The non-transitory machine-readable storage medium of claim 17 , wherein the instructions for verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency comprise:
instructions for counting a number of timing packets received via the second synchronous stream within a window;
instructions for estimating a number of timing packets expected to be received via the second synchronous stream within the window based on the local clock frequency; and
instructions for comparing the counted number to the estimated number.
20 . The non-transitory machine-readable storage medium of claim 17 , wherein the instructions for verifying the accuracy of the local clock frequency based on comparing the second synchronous stream to the local clock frequency comprises:
instructions for adding data into a buffer based on the second synchronous stream,
instructions for removing data from the buffer based on the local clock frequency, and
instructions for monitoring the buffer for at least one of overrun and underrun.