MINIMIZING SYMMETRICAL LATENCY IMPACT BY JITTER BUFFER FOR TDM CES
A method and system are provided for allowing time-alignment of teleprotection measurements of power signals. Teleprotection observations are communicated between teleprotection ends through a packet switched network. At each end of a teleprotection segment, a teleprotection device communicates with the network through a router providing CES and located at the edge of the network. Playout of the jitter buffers of the CES routers is initiated only if the PDV is acceptable such that confidence that the packets from each CES router to the associated teleprotection device are synchronized. The fill level of the jitter buffer is determined a number of times, and then the average of the determined fill levels is compared with an expected fill level. If the difference between the average of the determined fill levels and the expected fill level exceeds a threshold, then the TDM CES is restarted. This is repeated until the difference is acceptable, indicating that playout of each jitter buffer is initiated at the same time.
1 . A method of providing teleprotection services over a packet switched network, the packet switched network including a first router providing Circuit Emulation Service (CES) and in TDM communication with a first teleprotection device and a second router providing CES and in TDM communication with a second teleprotection device, the first router and the second router being separated by the packet switched network, the method comprising:
establishing a TDM CES between the first teleprotection device and the second teleprotection device;
at the first router, receiving packets into a jitter buffer;
at regular periods, determining the fill level of the jitter buffer;
after a configured number of such determinations, determining an average of the determined fill levels;
comparing the average of the determined fill levels with an expected fill level in order to evaluate a jitter buffer latency; and
if the comparison indicates that the jitter buffer latency is unacceptable, then restarting the TDM CES.
2 . The method of claim 1 wherein the comparison indicates that the jitter buffer latency is unacceptable if the absolute value of the difference between the average of the determined fill levels and the expected fill level exceeds a predetermined threshold.
3 . The method of claim 1 wherein the comparison indicates that the jitter buffer latency is unacceptable if the difference between the average of the determined fill levels and the expected fill level exceeds a predetermined threshold or if the difference between the average of the determined fill levels and the expected fill level is below zero.
4 . The method of claim 1 further comprising:
maintaining the TDM CES if the comparison indicates that the jitter buffer latency is acceptable; and
periodically:
determining the fill level of the jitter buffer at regular periods, determining an average of the determined fill levels after the configured number of such determinations, comparing the newly determined average with the expected fill level, and taking action if the comparison indicates that the jitter buffer latency is unacceptable.
5 . The method of claim 4 wherein the action comprises at least one of purchasing additional bandwidth within the packet switched network and generating an alarm.
6 . The method of claim 1 wherein the TDM CES is restarted a configurable number of times, after which at least one of generating an alarm and refraining from providing teleprotection services is carried out.
7 . A router providing Circuit Emulation Services (CES) to a first teleprotection device, comprising:
a jitter buffer;
a CESoP processor for establishing a TDM CES between the first teleprotection device and a second teleprotection device, receiving packets received over a packet switched network and placing the packets in the jitter buffer, and playing out the packets into a TDM bitstream to the first teleprotection device; and
a teleprotection supporter for determining the fill level of the jitter buffer at regular periods, determining an average of the determined fill levels after a configured number of such determinations, comparing the average of the determined fill levels with an expected fill level in order to evaluate a jitter buffer latency, and instructing the CESoP processor to restart the TDM CES if the comparison indicates that the jitter buffer latency is unacceptable.
8 . The router of claim 7 wherein the teleprotection supporter determines that the jitter buffer latency is unacceptable if the absolute value of the difference between the average of the determined fill levels and the expected fill level exceeds a predetermined threshold.
9 . The router of claim 7 wherein the teleprotection supporter determines that the jitter buffer latency is unacceptable if the difference between the average of the determined fill levels and the expected fill level exceeds a predetermined threshold or if the difference between the average of the determined fill levels and the expected fill level is below zero.
10 . The router of claim 7 wherein the teleprotection supporter periodically: determines the fill level of the jitter buffer at regular periods, determines an average of the determined fill levels after the configured number of such determinations, compares the newly determined average with the expected fill level, and takes action if the comparison indicates that the jitter buffer latency is unacceptable.
11 . The router of claim 10 wherein the action comprises at least one of purchasing additional bandwidth within the packet switched network and generating an alarm.
12 . The router of claim 7 wherein the teleprotection supporter instructs the CESoP processor a configurable number of times, after which the teleprotection supporter does at least one of generating an alarm and refraining from providing teleprotection services.