DCT

6:20-cv-00495

WSOU Investments LLC v. ZTE Corp

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 6:20-cv-00495, W.D. Tex., 11/06/2020
  • Venue Allegations: Venue is alleged based on Defendants’ places of business within the Western District of Texas, including a research and development center in Austin, and through the commission of infringing acts within the district.
  • Core Dispute: Plaintiff alleges that Defendant’s ZXR10 series of networking switches, which support the Quantized Congestion Notification protocol, infringe a patent related to advanced traffic flow control in data communications systems.
  • Technical Context: The technology concerns methods for managing network congestion by intelligently and selectively reducing the transmission rate of different types of data traffic based on granular feedback, aiming to prioritize critical data and maximize bandwidth utilization.
  • Key Procedural History: The patent-in-suit, U.S. Patent No. 9,258,232, was the subject of an Ex Parte Reexamination, which resulted in the cancellation of several claims and the amendment of the asserted independent claim 1. Specifically, reexamination added a new limitation requiring the generation of a "traffic preference message," which may significantly narrow the scope of the asserted claim compared to its original form.

Case Timeline

Date Event
2007-10-18 Priority Date for U.S. Patent No. 9,258,232
2016-02-09 Issue Date for U.S. Patent No. 9,258,232
2020-11-06 First Amended Complaint Filing Date

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 9,258,232: INGRESS TRAFFIC FLOW CONTROL IN A DATA COMMUNICATIONS SYSTEM (Issued Feb. 9, 2016)

The Invention Explained

  • Problem Addressed: The patent identifies a problem with conventional network flow control, where simple on/off "backpressure" signals treat all traffic identically. This can allow a flood of low-priority data to halt the flow of essential, high-priority network-control traffic, potentially causing network instability or data loss, while also leading to underutilized bandwidth when all traffic is stopped. (’232 Patent, col. 1:36-44, 1:52-59).
  • The Patented Solution: The invention describes an intelligent flow control system featuring a controller that receives "multi-priority" or "advanced" backpressure messages from a downstream device. (’232 Patent, col. 2:40-46). Unlike simple halt signals, these messages contain detailed information about the fill levels of various priority-specific receive queues. Based on this granular feedback and a configurable mapping table, the controller determines specific "weighting factors" (e.g., W1, W2, W3) to apply to rate limiters for different classes of traffic (e.g., High, Medium, Low), thereby selectively throttling data flows instead of halting them entirely. (’232 Patent, Fig. 1; col. 4:5-20). This method aims to prioritize critical traffic while maximizing overall throughput.
  • Technical Importance: This approach provides a more granular method for managing network congestion than binary on/off signaling, which is critical for maintaining performance and reliability in complex networks handling diverse types of data with varying priorities. (’232 Patent, col. 2:56-62).

Key Claims at a Glance

  • The complaint asserts infringement of at least independent claim 1. (Compl. ¶40).
  • The essential elements of independent claim 1, as amended by the Ex Parte Reexamination Certificate issued Dec. 11, 2024, are:
    • A method performed by a traffic flow control system for performing flow control on a flow of data packets for transmission over a link, comprising:
    • receiving, by a controller of the traffic flow control system, a backpressure signal, wherein the backpressure signal indicates a period of congestion;
    • determining, by the controller..., at least one weighting factor to be applied to the flow of data packets based on the received backpressure signal;
    • adjusting an amount of rate limiting applied to at least a portion of the flow of data packets based on both the determined at least one weighting factor and a content of the backpressure signal; and
    • generating a traffic preference message for transmission to a source of the flow of data packets, the traffic preference message indicating a type of data packet preferred for transmission over the serial link in accordance with the determined at least one weighting factor.
  • The complaint’s prayer for relief seeks judgment of infringement on "one or more claims" of the ’232 Patent, preserving the right to assert additional claims. (Compl. p. 16).

III. The Accused Instrumentality

Product Identification

The Accused Products are Defendant's ZXR10 5900 series and ZXR10 5960-H series routing switches. (Compl. ¶27).

Functionality and Market Context

The complaint describes the Accused Products as "next-generation" switches with high capacity and port density, intended for use in data centers and carrier aggregation scenarios. (Compl. p. 6). The infringement allegations focus on the products' support for the Data Center Bridging (DCB) protocol family, and specifically the Quantized Congestion Notification (QCN) protocol, which is part of the IEEE 802.1Q standard. (Compl. ¶¶26-28). The complaint alleges that the QCN protocol is used for traffic flow control and includes a "Congestion Point Algorithm" that generates feedback messages and a "Reaction Point Algorithm" that adjusts data flow rates in response to those messages. (Compl. ¶29). A screenshot from a ZTE datasheet shows the ZXR10 5960 Series Switches are marketed for cloud-computing data centers. (Compl. p. 6).

IV. Analysis of Infringement Allegations

’232 Patent Infringement Allegations

Claim Element (from Independent Claim 1, as amended) Alleged Infringing Functionality Complaint Citation Patent Citation
receiving, by a controller..., a backpressure signal, wherein the backpressure signal indicates a period of congestion; The Accused Products' Reaction Point (RP) algorithm receives a Congestion Notification Message (CNM), which indicates congestion at a Congestion Point (CP). A screenshot shows the QCN algorithm is composed of a CP and RP. ¶29 col. 5:8-12
determining, by the controller..., at least one weighting factor to be applied... based on the received backpressure signal; The Congestion Point Algorithm allegedly configures a "cpW (Congestion Point Weight)" variable, described as a "weight factor that applies to the change in queue length" and is used to calculate feedback. A screenshot from an IEEE standard details the "cpW" variable. ¶31 col. 5:13-17
adjusting an amount of rate limiting... based on both the determined at least one weighting factor and a content of the backpressure signal; The Reaction Point algorithm uses a Rate Limiter to adjust the "rpCurrentRate". This adjustment is a function of "dec_factor", which is dependent on the received feedback ("rpFb"), which in turn is calculated using the "cpW" (the alleged weighting factor). ¶¶37-39 col. 5:18-24
and generating a traffic preference message for transmission to a source... indicating a type of data packet preferred for transmission... The complaint does not appear to contain explicit allegations mapping to the "generating a traffic preference message" limitation, which was added to the claim during reexamination. N/A col. 5:34-45

Identified Points of Contention

  • Scope Questions: A primary question for claim construction will be whether the QCN protocol’s "cpW" parameter, as described in the complaint, constitutes a "weighting factor" within the meaning of the patent. The patent’s embodiment describes multiple distinct weighting factors (W1, W2, W3) corresponding to different traffic priorities, whereas the complaint describes a single "cpW" value used within a feedback calculation formula. (Compl. ¶31; ’232 Patent, Fig. 1).
  • Technical Questions: The complaint’s infringement theory appears to be based on the original, unamended version of claim 1. What evidence, if any, can the Plaintiff provide to demonstrate that the Accused Products perform the function of "generating a traffic preference message," a limitation added during reexamination to secure patentability and now essential for a finding of literal infringement? The complaint's supporting documents, such as the diagram of congestion detection in a QCN Congestion Point, do not show such a message being generated. (Compl. p. 10).

V. Key Claim Terms for Construction

The Term: "weighting factor"

  • Context and Importance: The infringement case hinges on mapping the accused QCN protocol’s "cpW" parameter to this claim term. Practitioners may focus on this term because the patent’s specification and figures appear to teach a different mechanism (multiple, discrete weights for different traffic types) than the one alleged in the complaint (a single weight variable in a feedback formula).
  • Intrinsic Evidence for a Broader Interpretation: The claim requires "at least one weighting factor," which could support an argument that a single factor like "cpW" is sufficient. (’232 Patent, col. 5:14). The term itself is not explicitly defined, potentially allowing for a broader functional interpretation.
  • Intrinsic Evidence for a Narrower Interpretation: The specification’s only detailed embodiment shows a plurality of weighting factors (W1, W2, W3) that correspond to distinct priority levels (High, Medium, Low) and are used to adjust respective rate limiters. (’232 Patent, Fig. 1; col. 4:18-20). This may support an interpretation that a "weighting factor" is one of a set of priority-specific values, not a general-purpose variable in a calculation.

The Term: "traffic preference message"

  • Context and Importance: This term was added to claim 1 during reexamination and is therefore critical to the claim's scope. Its interpretation will be central to the dispute, as the complaint does not appear to allege any corresponding functionality in the Accused Products.
  • Intrinsic Evidence for a Broader Interpretation: The patent does not define the exact format of this message, which a party could argue allows for flexibility. A party might contend that any signal that results in the preferential transmission of one data type over another could meet this limitation functionally.
  • Intrinsic Evidence for a Narrower Interpretation: The specification describes the "traffic preference message" (46) as a distinct signal generated by the controller (42) and sent to an "upstream data processor" to "inform the upstream unit of the most appropriate type of data that should be transmitted." (’232 Patent, Fig. 1; col. 5:34-45). This suggests it is a separate, affirmative message distinct from the "backpressure message" (40), and its purpose is to request a specific data type, not merely to report congestion.

VI. Other Allegations

  • Indirect Infringement: The complaint alleges induced infringement, stating that ZTE provides product descriptions, operating manuals, and other instructions that encourage and facilitate the use of the infringing QCN functionality. (Compl. ¶43). Several URLs for product datasheets are provided as examples of such materials. (Compl. ¶43).
  • Willful Infringement: Willfulness is alleged based on knowledge of the ’232 Patent obtained "since at least the date of service of this Complaint." (Compl. ¶42). The complaint does not allege pre-suit knowledge of the patent.

VII. Analyst’s Conclusion: Key Questions for the Case

  • A core issue will be one of post-reexamination scope: Can Plaintiff prove that the accused switches practice the "generating a traffic preference message" limitation, which was added to independent claim 1 during reexamination to overcome prior art? The absence of allegations mapping to this element in the complaint raises a significant question about the viability of the infringement claim as pleaded.
  • A second central question will be one of technical and functional mapping: Does the accused QCN protocol's use of a single "cpW" variable within a feedback calculation formula meet the "determining... at least one weighting factor" and "adjusting... rate limiting based on" that factor, as those limitations are understood in the context of the patent's disclosure of applying distinct, priority-based weights directly to rate limiters?
  • Finally, an evidentiary question will be whether discovery reveals functionality in the accused switches that is not described in the public-facing documents cited in the complaint, particularly any function that could plausibly be argued to meet the "traffic preference message" limitation, either literally or under the doctrine of equivalents.