News Column

Patent Issued for Message Synchronization over a Stochastic Network

June 25, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventors Picco, Martin Raptis (Santa Cruz, CA); Koren, Noam (Haniel, IL), filed on September 14, 2012, was published online on June 10, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8750409 is assigned to Harmonic, Inc. (San Jose, CA).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The following disclosure relates to network communication.

"In some communication systems, components need to adjust transmission parameters such as data rates or packet sizes during operation. In one possible scenario, a multiplexer that is connected to multiple variable bitrate encoders (e.g., in an MPEG-based video transmission system) may be configured to instruct the encoders to transmit data at a specific rate. For example, a multiplexer that delivers a constant bitrate stream to subscribers can instruct encoders to send at bitrates that correspond to the complexity of the signal that is being encoded, while ensuring that the sum of the individual encoder bitrates is not greater than the constant bitrate that the multiplexer has to provide. In this scenario, it is important that the encoders change transmission parameters when requested to do so such that data transmitted with the changed parameters from the multiple encoders can be multiplexed together. If, for example, one of the encoders did not reduce the bitrate of the encoded data for a frame, more bits might arrive at the multiplexer for the frame than the multiplexer could place in the constant-bitrate output stream. Such systems, in which high-precision synchronization is desirable, typically use a deterministic connection (e.g., a connection with a constant or predictable delay) for communication so that messages can be synchronized using deterministic delays.

"Components in a communication system can be connected using a stochastic (non-deterministic) network (e.g., a packet-based network using the internet protocol). A delay between the transmission of a message over a stochastic network and the receipt of the message typically is a random variable, so message synchronization can be difficult. Upper and lower bounds on the delay typically can be determined. For some stochastic networks, the upper bound on delay can be infinite (e.g., a packet can be lost and never arrive at the packet's destination), and for other stochastic networks the upper bound on delay can be finite."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "In one aspect, a method is provided for communicating between a local component and a remote component, where the local component is connected to the remote component using a non-deterministic communication link. A local clock of the local component is synchronized with a remote clock of the remote component to within a maximum offset. A rate message from the remote component is received at the local component, where the rate message includes a first time stamp. A data rate of the local component is adjusted using the rate message when the time of the local clock substantially matches a time determined using the first time stamp. A data message is sent from the local component to the remote component using the adjusted data rate, where the data message includes a second time stamp for use in processing data in the data message.

"Particular implementations may include one or more of the following features. A complexity message is transmitted from the local component to the remote component, and the rate message is produced using the complexity message. Adjusting the data rate includes determining the first time of the local clock using a phase-locked loop or statistically estimating the first time of the local clock. The time determined using the first time stamp is further determined using information about a communication link delay and/or information about an offset between the local clock and a remote clock. The information about an offset includes information about a maximum offset, which can include a maximum positive offset and a maximum negative offset. The information about a communication link delay includes information about a maximum communication link delay between the local component and the remote component, which can include information about a delay from the remote component to the local component and information about a delay from the local component to the remote component.

"The first time stamp includes the information about the communication link delay and/or the information about the offset between the local clock and the remote clock. The second time stamp includes information about the communication link delay and/or information about the offset between the local clock and the remote clock. Adjusting a data rate includes queuing rate information included in the rate message. The rate message is buffered until the first time of the local clock substantially matches the time determined using the first time stamp.

"In another aspect, a method is provided for communicating between a local component and a remote component, where the local component is connected to the remote component using a non-deterministic communication link, and a local clock of the local component is synchronized with a remote clock of the remote component to within a maximum offset. A rate message is sent from the local component to the remote component. The rate message includes a first time stamp that is used by the remote component to send a data message to the local component using a data rate included in the rate message when a first time of a remote clock substantially matches a time determined using the first time stamp. The data message is received at the local component, where the data message includes a second time stamp. Data included in the data message is processed using the second time stamp.

"Particular implementations may include one or more of the following features. A complexity message is received from the remote component, and the rate message is generated using the complexity message. The data included in the data message is processed when a second time of a local clock substantially matches a time determined using the second time stamp. The time determined using the second time stamp is further determined using information about a communication link delay and/or information about an offset between the local clock and the remote clock. The information about the offset includes information about a maximum offset, which can include information about a maximum positive offset and a maximum negative offset.

"The information about a communication link delay includes information about a maximum communication link delay between the local component and the remote component, which can include information about a delay from the remote component to the local component and information about a delay from the local component to the remote component. The second time stamp includes the information about the communication link delay and/or the information about the offset between the local clock and the remote clock. The first time stamp includes information about the communication link delay and/or information about the offset between a local clock and the remote clock. Processing data included in the data message includes buffering the data message until a time of the local clock substantially matches a time determined using the second time stamp.

"In another aspect, a method is provided for communicating between a local component and a remote component. A non-deterministic communication link connecting the local component to the remote component is provided. A local clock of the local component is synchronized with a remote clock of the remote component to within a maximum offset. A rate message is sent from the remote component to the local component, where the rate message includes a first time stamp. A data rate of the local component is adjusted using the rate message when a first time of the local clock substantially matches a time determined using the first time stamp, information about a communication link delay, and information about the maximum offset. A data message is sent at the first time from the local component to the remote component using the adjusted data rate, where the data message includes a second time stamp. Data included in the data message is processed when a second time of the remote clock substantially matches a time determined using the second time stamp, information about the communication link delay, and information about the maximum offset.

"Particular implementations may include one or more of the following features. The local component is an encoder and the remote component is a multiplexer. A complexity message is transmitted from the local component to the remote component, where the rate message is produced using the complexity message.

"In one aspect, a local component is provided that is connected to a remote component using a non-deterministic communication link. The local component includes means for synchronizing a local clock of the local component to a remote clock of the remote component to within a maximum offset and means for adjusting a data rate of the local component using a rate message from the remote component. The local component also includes means for guaranteeing that a data message sent from the local component to the remote component will arrive at the remote component in time to be processed by the remote component.

"Particular implementations may include one or more of the following features. The means for synchronizing include a phase-locked loop. The means for synchronizing include statistical estimation. The means for adjusting include a rate adjustment unit. The means for guaranteeing include a time-stamping component.

"In another aspect, a multiplexer is provided that includes an output assembly unit, which assembles data into an output stream. An input unit receives a data message including data and a time stamp and provides the data to an output assembly unit when a time of a local clock substantially matches a time determined using the time stamp. A rate control unit sends a time-stamped rate message to a remote component, where the rate message includes information about a data rate of a future data message.

"Particular implementations may include one or more of the following features. The rate control unit generates the rate message using information about a complexity of the future data message. The rate control unit timestamps the rate message using information about the time of the local clock. The input unit provides the data to the output assembly unit using information about a communication link delay and/or information about an offset between the local clock and a remote clock.

"In another aspect, an encoder is provided that includes a synchronization unit, which synchronizes an encoder clock with a remote clock to within a maximum offset. A transmitter time stamps and transmits a data message at a data rate, and a rate adjustment unit adjusts the data rate responsive to a corresponding rate message when a time of the encoder clock substantially matches a time determined using a time stamp in the corresponding rate message.

"Particular implementations may include one or more of the following features. The synchronization unit includes a phase-locked loop. The transmitter time stamps the data message using information about the time of the encoder clock. The rate adjustment unit adjusts the data rate using information about a communication link delay and/or information about the maximum offset. The transmitter transmits a timestamped complexity message that is used to generate the corresponding rate message.

"Implementations can include one or more of the following advantages. Methods and apparatus are disclosed that can be used to allow communication components to synchronize messages accurately using a stochastic network. Systems or components designed to communicate over a deterministic network can be configured to allow communication over the stochastic network. Components in a communication system can be located remotely without being directly connected using a dedicated communication link. Connections between components in the communication system can be changed dynamically without requiring rewiring. A small pool of backup devices can be used in the communication system because the connections can be changed dynamically and are very flexible. Variations in message delivery times can be kept small, even when using a stochastic network having large delays and/or large variations in delay.

"The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims."

URL and more information on this patent, see: Picco, Martin Raptis; Koren, Noam. Message Synchronization over a Stochastic Network. U.S. Patent Number 8750409, filed September 14, 2012, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8750409.PN.&OS=PN/8750409RS=PN/8750409

Keywords for this news article include: Harmonic Inc.

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Source: Journal of Engineering


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