Symmetricom Patent Grants

Method for generating a robust timing correction in timing transfer systems

Granted: February 4, 2014
Patent Number: 8644348
High accuracy timing over packet networks is achieved by generating correction factors from multiple separation intervals and timing information contained in packets in both directions between a master and a slave. The methods are based on evaluating the weighted average of short-term, medium-term, and long-term measurements of local clock offset. Weighted averages are used to develop robust correction terms that are modified with an ?-shaping factor to provide additional immunity to…

Precise clock synchronization over optical fiber

Granted: December 3, 2013
Patent Number: 8600239
A clock at a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other is aligned using optical timing signals having different wavelengths. Transit delays between the first and second network elements may be determined using the same optical timing signals.

Precision time transfer over optical fiber

Granted: November 26, 2013
Patent Number: 8594134
A clock at a first network element that is connected to a second network element over an optical fiber link is aligned using bursts of timing information exchanged between the two network elements. According to one method, the bursts from the first network element to the second network element and the bursts from the second network element to the first network element are transmitted over the same wavelength channel of the optical fiber link, in which case zero asymmetry in the transit…

Network time protocol precision timestamping service

Granted: May 28, 2013
Patent Number: 8451867
Embodiments of the present invention set forth a method and system for reducing uncertainty in receive and transmit timestamps created by an NTP server. The uncertainty in the receive timestamps is removed by recording the time-of-arrival in the hardware clock of the NTP server before the incoming packets may be delayed by traversing the various layers of software in a timestamping system. The uncertainty in the transmit timestamps is removed by giving the outgoing packets a timestamp in…

Method and system for analyzing and qualifying routes in packet networks

Granted: April 23, 2013
Patent Number: 8427963
Routes of a packet network are analyzed according to various transit delay metrics. Preferred packet network routes are selected between source and destination based on these metrics. In packet networks employing boundary clocks and transparent clocks, faulty boundary clocks and faulty transparent clocks are identified using the metrics.

Method and apparatus for finding latency floor in packet networks

Granted: February 26, 2013
Patent Number: 8385212
A latency floor between two nodes of a packet-switched network is estimated using transit times of a group of packets traversing the two nodes. In particular, a periodically generated histogram of packet transit times is used to estimate the latency floor. In some packet-switched networks, the behavior of some network elements changes drastically when the network is congested. Because latency floor cannot be accurately estimated under such conditions, packet transit times collected…

Method and apparatus for analyzing and qualifying packet networks

Granted: September 25, 2012
Patent Number: 8274999
Packet network performance is assessed using transit delay metrics and compliance masks generated at various evaluation nodes of the network. The evaluation nodes may employ network probes that make precise measurements of transit delays and thereby of transit delay variations. Based on the assessments, a master may be added to the network or relocated within the network, rate of timing packets generated by the master may be adjusted up or down, or oscillators used at the slaves may be…

Method and apparatus for monitoring packet networks

Granted: January 31, 2012
Patent Number: 8107502
A packet probe for a packet network accurately generates and monitors packets within the network. The packet probe supports packet generation and packet transmission. When a packet is ready for transmission, a hardware-based time stamp unit affixes a time stamp to the packet reflecting an actual transmission time. The packet probe also supports receiving, filtering, and time stamping received packets. When a packet is received, a packet filter determines whether the received packet…

Enhanced clock control in packet networks

Granted: November 22, 2011
Patent Number: 8064484
One embodiment of the present invention sets forth a method for autonomously validating the time and frequency data obtained from multiple sources, and generating a suitable estimate of the frequency difference between the client clock and the source. The method includes the steps of protocol data unit validation, offset measurement, minimum offset filtering, and frequency filtering. With these steps, the negative effects of packet delay variation may be mitigated and a frequency…

Adaptive play-out buffers and adaptive clock operation in packet networks

Granted: February 22, 2011
Patent Number: 7894489
Methods and apparatus for a play-out buffer that may adjust offsets between clocks of two ends of a network link with an adaptive play-out buffer and adaptive clock control. The play-out buffer is a circular jitter buffer that permits the absorption of a frequency offset using controlled slips between two nodes of a network. The play-out buffer also accommodates some wander introduced by the time-delay variation across the network. The adaptive clock control reduces the frequency offset…

Network time transfer

Granted: January 25, 2011
Patent Number: 7876788
The invention comprises a method and apparatus for reducing uncertainty in timing on the network. The uncertainty in receive buffers is removed by time stamping the arriving packets before sending the packets to the receive buffer. The uncertainty in the transmission buffer is removed by giving the packets a timestamp in the future, and holding the packets until precisely that time. Time precision is ensured by only releasing time packets at the host physical layer to network boundary at…

Supporting synchronization status messages on building integrated timing supply synchronization supply unit remote shelves

Granted: February 9, 2010
Patent Number: 7660332
Systems and methods are described for supporting synchronization status messages (SSM) on building integrated timing system synchronization supply unit (BITS-SSU) remote shelves. A method includes providing a composite clock reference to a remote synchronization supply unit from a master synchronization supply unit; providing a synchronization status message to the remote synchronization supply unit; relaying the composite clock reference from the remote synchronization supply unit; and…

Adaptive play-out buffers and clock operation in packet networks

Granted: December 22, 2009
Patent Number: 7636022
Methods and apparatus are described for a play-out buffer. A method includes writing a data packet into a jitter buffer at a write address specified by a write address generator; incrementing the write address generator; generating the difference between the write address and a current read address specified by a read address generator; reading a data packet from the jitter buffer from the current read address specified by the read address generator; generating a new read address based…

Network forwarding device and method that forward timing packets through the device with a constant delay

Granted: December 15, 2009
Patent Number: 7633870
The variable latency associated with standard network forwarding devices is eliminated by forwarding timing packets through a network forwarding device with a constant delay. The network forwarding device of the invention time stamps timing packets that are received by the input ports with a predefined future time, and then outputs the timing packets from the output ports at the predefined time so that the transmission delay through the network forwarding device is the same from any port…

Image complexity computation in packet based video broadcast systems

Granted: October 27, 2009
Patent Number: 7609769
A method to determine real time image complexity in video streaming, IPTV and broadcast applications using a statistical model representing channel bandwidth variation and image complexity that considers scene content changes. Available channel bandwidth is distributed unevenly among multiple video streams in proportion to bandwidth variation and image complexity of the broadcast video stream. The distribution of available channel bandwidth is determined based upon an image complexity…

Multiple transmission bandwidth streams with defferentiated quality of service

Granted: May 19, 2009
Patent Number: 7535900
Methods and apparatus are described for providing multiple transmission bandwidth streams with differentiated quality of service on a inter-machine trunk. One approach includes time-division multiplexing. Another approach includes statistical multiplexing. Another approach includes packet segmentation. The approaches are commercially important because they significantly reduce time-delay variation.

Two-way timing protocol

Granted: May 19, 2009
Patent Number: 7535931
A two-way time transfer protocol includes: sending a signal from a first node including a first clock and a first time interval counter coupled to the first clock over a transport physical layer coupled to the first node to a second node coupled to the transport physical layer, the second node including a second clock and a second time interval counter coupled to the second clock; then sending a last second node time interval counter value from the second time interval counter of the…

Distribution of synchronization in an ethernet local area network environment

Granted: June 3, 2008
Patent Number: 7382845
Systems and methods are described for distribution of synchronization in a packet switched local area network environment. A method for extracting network synchronization timing from a data transmission burst includes: recovering a clock during the data transmission burst; and then holding over the clock after the data transmission burst ceases. A method for inserting network synchronization timing into a data transmission burst includes encoding data using a time-base reference signal…

Modified asymmetric digital subscriber line for use with long loops

Granted: April 29, 2008
Patent Number: 7366286
Systems and methods are described for modified asymmetric digital subscriber line for use with long loops. A method includes modifying a digital signal processor including reallocating a portion of an original guard band to a modified downstream band and reallocating a portion of an original upstream band to a modified guard band. An apparatus includes a digital signal processor defining an expanded downstream band; and a high pass filter coupled to the digital signal processor to…

Bonded G.shdsl links for ATM backhaul applications

Granted: March 25, 2008
Patent Number: 7349401
Systems and methods are described for deploying bonded G.shdsl links for ATM backhaul applications. A method includes transporting digital data including: coupling a first end of a plurality of unbundled network elements to a first modem; coupling a second end of the plurality of unbundled network elements to a second modem; providing the first modem with a first single stream of asynchronous transfer mode cells; sequence-cell division multiplexing to divide the first single stream of…