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EP-4487503-B1 - METHOD OF MEASURING TIMING HOLDOVER PERFORMANCE IN AN R-PHY SYSTEM

EP4487503B1EP 4487503 B1EP4487503 B1EP 4487503B1EP-4487503-B1

Inventors

  • NEUGEBOREN, Yair

Dates

Publication Date
20260513
Application Date
20230228

Claims (11)

  1. A remote device of a distributed access architecture of a communications network, the remote device operatively connected to a core providing data to the remote device, the remote device including a dejitter buffer and a processor configured to measure sequential values, each value representing an instantaneous fullness state of the dejitter buffer, and use the values to determine a magnitude of drift of a first clock of the remote device relative to a second clock of the core; wherein the remove device includes a low pass filter that filters the sequential values, wherein the output of the low pass filter is used to determine a sequence of fractional frequency offset values.
  2. The remote device of claim 1 comprising an remote physical device, RPD.
  3. The remote device of claim 1 where the low pass filter blocks variations in the sequential values due to network jitter.
  4. The remote device of claim 1 where the processor accumulates the sequence of fractional frequency offset values to provide an accumulated value and compares the accumulated value to a threshold.
  5. The remote device of claim 4 where the remote device provides an alert based on the comparison.
  6. A method comprising: measuring sequential values representing a fullness state of a dejitter buffer of a first network device having a first clock; and using the sequential values to determine a magnitude of drift of the first clock relative to a second clock associated with a second device providing data to the dejitter buffer; wherein the method includes applying a low pass filter to the sequential values, wherein the output of the low pass filter is used to determine a sequence of fractional frequency offset values.
  7. The method of claim 6 where the first network device is at least one of a remote physical device, RPD, and a remote MACPHY device, RMD.
  8. The method of claim 6 where the low pass filter blocks variations in the sequential values due to network jitter.
  9. The method of claim 6 including accumulating the sequence of fractional frequency offset values to provide an accumulated value.
  10. The method of claim 9 including comparing the accumulated value to a threshold.
  11. The method of claim 10 including providing an alert based on the comparison.

Description

CROSS REFERENCE TO RELATED APPLICATIONS The present application claims priority to U.S. Provisional Application. No. 63/314,904 filed February 28, 2022. BACKGROUND The subject matter of this application generally relates to delivery of video content using distributed access architectures (DAA) of a hybrid CATV network, and more particularly to architectures that distribute the functions of the Cable Modem Termination System between a core and a remote device synchronized to the core, such as a Remote PHY device or Remote MACPHY device. Although Cable Television (CATV) networks originally delivered content to subscribers over large distances using an exclusively RF transmission system, modem CATV transmission systems have replaced much of the RF transmission path with a more effective optical network, creating a hybrid transmission system where cable content terminates as RF signals over coaxial cables, but is transmitted over the bulk of the distance between the content provider and the subscriber using optical signals. Specifically, CATV networks include a head end at the content provider for receiving signals representing many channels of content, multiplexing them, and distributing them along a fiber-optic network to one or more nodes, each proximate a group of subscribers. The node then de-multiplexes the received optical signal and converts it to an RF signal so that it can be received by viewers. The system in a head end that provides the video channels to a subscriber typically comprises a plurality of EdgeQAM units operating on different frequency bands that are combined and multiplexed before being output onto the HFC network. A traditional HFC architecture includes a head end having a Cable Modem Termination System (CMTS), used to provide high speed data services, such as video, cable Internet, Voice over Internet Protocol, etc. to cable subscribers. Typically, a CMTS will include both Ethernet interfaces (or other more traditional high-speed data interfaces) as well as RF interfaces so that traffic coming from the Internet can be routed (or bridged) through the Ethernet interface, through the CMTS, and then onto the optical RF interfaces that are connected to the cable company's hybrid fiber coax (HFC) system. Downstream traffic is delivered from the CMTS to a cable modem in a subscriber's home, while upstream traffic is delivered from a cable modem in a subscriber's home back to the CMTS. Many modem HFC CATV systems have combined the functionality of the CMTS with the video delivery system in a single platform called the Converged Cable Access Platform (CCAP). In these traditional HFC architectures, the video is modulated onto the RF network by a video Edge QAM (VEQ). A VEQ receives Internet-Protocol (IP) encapsulated Single & Multiple Program Transport Streams (SPTSs & MPTSs) from various sources (unicast / multicast) and, after removing any jitter from the network ingress stream, statically or dynamically maps these streams onto a QAM channel via one or more ports of the VEQ, remapping program identifiers (PIDs), while multiplexing as necessary individual SPTSs into a single MPTS. The VEQ may also perform local encryption of the video's elementary streams (ESs). As networks have expanded and head ends have therefore become increasingly congested with equipment, many content providers have recently used distributed architectures to spread the functionality of the CMTS/CCAP throughout the network. This distributed architecture keeps the cable data and video signals in digital format as long as possible, extending the digital signals beyond the CMTS/CCAP deep into the network before converting them to RF. It does so by replacing the analog links between the head end and the access network with a digital fiber (Ethernet/PON) connection. One such distributed architecture is Remote PHY (R-PHY) distributed access architecture that relocates the physical layer (PHY) of a traditional CMTS or CCAP - including the VEQs - by pushing the physical layer to the network's fiber nodes. Thus, while the core in the CMTS/CCAP performs the higher layer processing, the R-PHY device in the node converts downstream video data packets sent by the core from digital to analog to be transmitted on radio frequency, and also converts the upstream RF data sent by cable modems from analog to digital format to be transmitted optically to the core. Another distributed access architecture is Remote MAC PHY (R-MACPHY) where, not only is the physical layer of the traditional CMTS pushed into the network, but the functionality Media Access Control (MAC) layer, which is one of the two layers that constitute the data link layer of a transport stream, is also assigned to one or more nodes in the network in what is called a Remote MACPHY device (RMD). In DAA architectures, it is therefore the remote video capable devices, such as an RMD and RPD, that include the VEQs that modulate a fully formed MPTS stream, sent by a core, onto the R