Time measurements in a transmission path
First Claim
1. In a communication system comprising a first and a second communication interface coupled by a transmission path, method of determining round-trip signal transmission delay through the path, comprising the steps of:
- transmitting through the path a first signal indicating time of its transmission from the first interface to the second interface;
transmitting through the path a second signal from the second interface to the first interface in response to receipt of the first signal at the second interface, the second signal indicating the time of transmittal of the first signal; and
determining, in response to receipt of the second signal at the first interface, the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay through the path.
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Accused Products
Abstract
In a voice packet switching network (10), following call path set-up, continuity packets (500a-c) are transmitted between the call originating (100) and destination (101) nodes to check call path continuity. The continuity packets carry time stamps of their (503) and the preceding continuity packet'"'"'s (504) time of transmission, to permit determination of call path transit delay, and computation of asynchrony between clocks (200) of the two nodes. A call path is considered acceptable if one half the path round trip transit delay does not exceed a predetermined maximum acceptable delay. Subsequently transmitted data packets are discarded if their transit delay exceeds the predetermined maximum acceptable delay. Transit delay of a data packet is computed from originating and terminating node clock readings at the time of transmission and reception of the packet, respectively, adjusted for asynchrony of the two clocks.
176 Citations
29 Claims
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1. In a communication system comprising a first and a second communication interface coupled by a transmission path, method of determining round-trip signal transmission delay through the path, comprising the steps of:
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transmitting through the path a first signal indicating time of its transmission from the first interface to the second interface; transmitting through the path a second signal from the second interface to the first interface in response to receipt of the first signal at the second interface, the second signal indicating the time of transmittal of the first signal; and determining, in response to receipt of the second signal at the first interface, the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay through the path. - View Dependent Claims (2, 3, 4)
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5. In a communication system comprising a first and a second communication interface coupled by a transmission path, each interface including time-indicating means, method of synchronizing the time-indicating means of the first and the second interface, comprising the steps of:
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transmitting through the path a first signal indicating time of its transmittal from the first interface to the second interface; transmitting through the path a second signal from the second interface to the first interface in response to receipt of the first signal at the second interface, the second signal indicating the time of transmittal of the first signal and the time of transmittal of the second signal; determining, in response to receipt of the second signal at the first interface, the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay through the path; determining the difference between the time of receipt of the second signal and the time of transmittal of the second signal plus half of the delay to obtain the time period of asynchrony between the time-indicating means of the first and the second interface; and adjusting the time-indicating means of the first interface by the time period of asynchrony to synchronize the time-indicating means of the first and the second interface. - View Dependent Claims (6)
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7. In a communication system comprising a first and a second communication interface interconnected by a transmission path, method of controlling communications passing between the first and the second interface, comprising the steps of:
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transmitting through the path a first signal indicating time of its transmittal from the first interface to the second interface; transmitting through the path, in response to receipt of the first signal at the second interface, a second signal from the second interface to the first interface, the second signal indicating the time of transmittal of the first signal; determining, in response to receipt of the second signal at the first interface, the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay through the path; comparing half of the transmission delay with a predetermined maximum acceptable one-way delay; and ceasing further transmissions between the first and second interface over the path when the half of the transmission delay exceeds the predetermined delay. - View Dependent Claims (8, 9, 10)
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11. In a packet switching network that includes a first communication node having a first clock and a second communication node having a second clock, the nodes interconnected by at least one transmission path, method of controlling communications between the nodes comprising the steps of:
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setting up a communication path over one of the at least one transmission path; transmitting over the communication path a first packet from the first node to the second node, the first packet bearing a first time stamp that represents the time indicated by the first clock at transmittal of the first packet; transmitting over the communication path a second packet from the second node to the first node in response to receipt of the first packet at the second node, the second packet bearing the first stamp and a second time stamp that represents the time indicated by the second clock at transmittal of the second packet; determining at the first node, in response to receipt of the second packet at the first node, the time period of asynchrony between the first and second clocks as half of the sum of the first stamp and the time indicated by the first clock at receipt of the second packet, less the second stamp; determining at the first node the one-way transmission delay through the communication path as the time indicated by the first clock at receipt of the second packet less the sum of the time period of asynchrony determined at the first node and the second stamp; comparing the transmission delay determined at the first node with a predetermined maximum acceptable one-way delay; and taking down the communication path when the transmission delay determined at the first node exceeds the predetermined delay. - View Dependent Claims (12, 13, 14)
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15. In a communication system that includes a first and a second communication interface coupled by a transmission path, apparatus for determining round-trip signal transmission delay through the path comprising:
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means associated with the first interface for transmitting through the path a first signal indicating time of its transmittal from the first interface to the second interface; means associated with the second interface and responsive to receipt of the first signal at the second interface for transmitting through the path a second signal from the second interface to the first interface, the second signal indicating the time of transmittal of the first signal; and first means associated with the first interface and responsive to receipt of the second signal at the first interface for determining the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A first communication interface for determining round-trip signal transmission delay through a transmission path of a communication system that includes the first and a like second communication interface connected by the the path, the first interface comprising:
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means for transmitting through the path a first signal indicating time of its transmittal from the first interface to the second interface; means, responsive to receipt of a second signal transmitted by the second interface to the first interface through the path upon receipt by the second interface of the first signal, the second signal indicating the time of transmittal of the first signal, for determining the difference between the time of transmittal of the first signal and the time of receipt of the second signal to obtain the round-trip transmission delay through the path. - View Dependent Claims (22, 23, 24, 25)
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26. A second interface for determining round-trip signal transmission delay through a transmission path of a communication system that includes the second and a like first communication interface connected by the path, the second interface comprising:
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means, responsive to receipt by the second interface of a first signal transmitted through the path by the first interface, the first signal indicating time of its transmittal from the first interface, for transmitting through the path to the first interface a second signal indicating the time of transmittal of the first signal and the time of transmittal of the second signal; means, responsive to receipt by the second interface of a third signal transmitted through the path by the first interface upon receipt of the second signal, the third signal indicating the time of transmittal of the second signal, for determining the difference between the time of transmittal of the second signal and the time of receipt of the third signal to obtain the round-trip transmission delay through the path. - View Dependent Claims (27, 28, 29)
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Specification