Session Link Research Sues Ribbon in Marshall Over a VoLTE Transit Network Signaling Patent.

Session Link Research LLC filed Session Link Research LLC v. Ribbon Communications Inc., No. 2:26-cv-00996 (E.D. Tex., Marshall Division), on November 3, 2026. The complaint describes the plaintiff as a Texas limited liability company and Ribbon, on information and belief, as a Delaware corporation with its principal place of business in Plano, Texas. For venue under 28 U.S.C. §§ 1391 and 1400(b), the complaint alleges that Ribbon maintains a regular and established place of business at its United States headquarters in Plano. The docket shows the case assigned to Judge Rodney Gilstrap and referred to Magistrate Judge Roy S. Payne. The plaintiff demands a jury.

The patent

The complaint asserts one patent, U.S. Patent 9,392,436, "Method and Apparatus for Voice Over LTE," issued July 12, 2016. It says the patent relates to a transit network that handles signaling messages between service provider networks and that the technology was developed by the named inventors, Richard H. Xu and Hwan Jang Tang, at the company that was the patent's original applicant and assignee. The patent issued from Application No. 14/212,290, filed March 14, 2014. The exemplary claim is claim 1, which the complaint describes as a method of handling signaling messages at a transit network connected between mobile networks: receiving a session control message from a mobile network, determining a signaling type associated with it, and routing it by domain routing if the type is roaming signaling and by called party routing if it is non-roaming signaling.

The accused products

The accused products are Ribbon Session Border Controllers, Policy and Routing Servers, and IMS Core / Cloud-Native IMS, with associated hardware and software. The complaint maps claim 1 to the Ribbon SBC acting as an interconnection border control function (I-BCF), relying on 3GPP TS 24.229 for how the function detects roaming indicators such as the g.3gpp.trf and g.3gpp.loopback feature capability parameters and routes requests accordingly.

What the complaint alleges

The single count alleges direct infringement under 35 U.S.C. § 271, induced infringement, and contributory infringement under § 271(c). It pleads knowledge at least as of the date of the complaint and, in the alternative, alleges on information and belief that Ribbon was willfully blind through a policy of not reviewing the patents of others. It says the plaintiff, and on information and belief prior assignees and licensees, complied with the marking statute.

Relief requested

The prayer asks for a judgment of direct infringement, a permanent injunction under § 283, damages no less than a reasonable royalty with interest and costs, and an exceptional case finding with attorneys' fees under § 285.

Where the case stands

Through November 4, 2026, the docket shows the complaint with the patent as Exhibit 1, the patent and trademark form, the plaintiff's disclosure statement, notices of appearance, and a summons issued to Ribbon on November 4. Session Link Research filed three other patent suits in the Marshall Division the same day, Nos. 2:26-cv-00992, 2:26-cv-00994, and 2:26-cv-00995. Watch for service on Ribbon and its answer or a motion. The case can end at any time, including by settlement or voluntary dismissal.