Method of detecting drift between two clocks
First Claim
1. A clock drift evaluator comprising:
- a. a time stamp extractor for extracting time stamp values from each received data packet of a data stream, the time stamp values being generated by a source clock;
b. an arithmetic unit providing a time difference value between the time stamp value extracted from each received data packet and a current local time value derived from a local clock;
c. comparison means comparing the time difference value against a time reference value to determine whether each received data packet is one of;
an early received packet, an on-time received packet, and a late received packet;
d. means for providing an evaluation of clock drift based on indications of an extent of early and late packet arrivals.
1 Assignment
0 Petitions
Accused Products
Abstract
A method of and apparatus for detecting drift between two clocks is presented. The apparatus comprises a hardware implementation of a clock drift evaluator. The evaluator monitors received packets associated with a data stream, and extracts a time stamp generated by a source clock from each packet. A difference d between the extracted time stamp and the local time is compared against a d_ref value to determine whether the packet was received early or late. On a prescribed schedule, the degree of late and early receipt of packets is compared against a tolerance level to determine whether a relative drift exists between the pacing of the source clock and the pacing of the local clock. The detection of drift between the two clocks provides support for service level guarantees in provisioning data streaming services in packet-switched environments.
151 Citations
23 Claims
-
1. A clock drift evaluator comprising:
-
a. a time stamp extractor for extracting time stamp values from each received data packet of a data stream, the time stamp values being generated by a source clock;
b. an arithmetic unit providing a time difference value between the time stamp value extracted from each received data packet and a current local time value derived from a local clock;
c. comparison means comparing the time difference value against a time reference value to determine whether each received data packet is one of;
an early received packet, an on-time received packet, and a late received packet;
d. means for providing an evaluation of clock drift based on indications of an extent of early and late packet arrivals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A method of detecting clock drift between two clocks comprising the steps of:
-
a. extracting a time stamp value generated by a source clock from each received packet of a monitored data stream downstream from the source clock;
b. deriving a time difference value between the stamp value and a current local time value provided by a local clock;
c. determining whether each received data packet is one of;
an early received packet, an on-time received packet, and a late received packet;
d. determining whether clock drift exists between the source clock and the local clock by comparing degrees of late and early packet arrivals against an adjustment threshold level. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
-
Specification