Session Link Research Sues AT&T in Marshall on Seven Network and Calling Patents.

Session Link Research LLC filed Session Link Research LLC v. AT&T Mobility LLC, No. 2:26-cv-00992 (E.D. Tex., Marshall Division), on November 3, 2026, against AT&T Mobility LLC, AT&T Services, Inc., and AT&T Enterprises LLC. The complaint describes the plaintiff as a Texas limited liability company based in Marshall, Texas, AT&T Mobility as a Delaware limited liability company based in Atlanta, Georgia, AT&T Services as a Delaware corporation, and AT&T Enterprises as a Delaware limited liability company. The docket shows the case assigned to Judge Rodney Gilstrap and referred to Magistrate Judge Roy S. Payne. The plaintiff demands a jury.

The seven patents

The complaint asserts seven patents, each attached as an exhibit, which Session Link says it owns outright (paragraphs 13 to 20): U.S. Patent 9,961,209, "Codec Selection Optimization," issued May 1, 2018; U.S. Patent 9,392,436, "Method and Apparatus for Voice Over LTE," issued July 12, 2016; U.S. Patent 8,265,062, "System and Method for Accomplishing Special Call Treatment in a Voice Over Internet Protocol Telephone System," issued September 11, 2012; U.S. Patent 9,083,771, "System and Methods for Multi-Participant Teleconferencing Using Preferred Forms of Telecommunication," issued July 14, 2015; U.S. Patent 10,057,429, "Pre-Paid Voice Calling Using Sponsored Data Roaming," issued August 21, 2018; U.S. Patent 11,284,459, "Data Access Security," issued March 22, 2022; and U.S. Patent 10,979,462, "Identifying Voice Over LTE Users," issued April 13, 2021. The complaint says the named inventors developed the technology of the '209, '436, '062, and '771 patents at one company, which all seven patents list as their assignee (paragraphs 27 to 30).

The exemplary claims are claim 1 of the '209, '436, '062, and '462 patents, claim 11 of the '771 patent, claim 15 of the '429 patent, and claim 24 of the '459 patent (paragraphs 35, 50, 65, 82, 102, 119, and 135).

The complaint describes the '209 patent as providing listings of codecs for offers and answers, the '436 patent as a transit network that handles signaling messages between service provider networks, the '062 patent as special treatment of an internet telephone call routed from an originating gateway to a destination gateway, and the '771 patent as a teleconferencing system in which a telecommunication manager sets up connections with participants (paragraphs 27 to 30). Claim 15 of the '429 patent recites a system with a calling service that receives connection information from a mobile device over a packetized data path that includes a data roaming connection between a visited network and the home network, determines a call rate from that information, places the call, and carries the call audio over that path. Claim 24 of the '459 patent recites authenticating, in a GRX or IPX interconnect network, the network and subscriber information in a GTP request to create a new session, and blocking the GTP tunnel when the request cannot be authenticated. Claim 1 of the '462 patent recites requesting from an IP exchange, based on a terminating user's identifier, a service identifier for the type of service that user is provisioned for on another operator's network, and using it to choose how to route the call.

The accused network

The accused products are AT&T's 5G and 5G+ network, including the AT&T 5G Standalone Core or AT&T's independent 5G Core, data centers, 5G cellular base stations (including 5G and 5G+ base stations), 5G hardware, software, radio units, and baseband units, and associated equipment, services, and platforms such as AT&T PREPAID (paragraph 25). The complaint alleges, on information and belief, that AT&T's 5G and 5G+ networks, AT&T 5G Standalone Core and independent 5G Core, and IMS networks are designed and operated in compliance with 3GPP, GSMA, and IETF standards, including those governing VoLTE, VoNR, SIP and SDP signaling, codec negotiation, inter-operator connectivity, and roaming (paragraph 26).

Count by count, the complaint maps the '209 patent to codec negotiation in AT&T's 5G core and IMS core for VoNR calls, relying on 3GPP TS 23.228 and TS 24.229 for how interconnection border functions process SDP offers and answers (paragraphs 35 and 36); the '436 patent to AT&T's mobile networks that support IMS-based VoLTE and VoNR (paragraph 50); the '771 and '429 patents to its 4G LTE and 5G networks that support IMS-based VoLTE and VoNR (paragraphs 82 and 102); the '062 patent to its 5G network with IMS-based voice services, a 5G core, and an IMS network (paragraph 65); the '459 patent to its 4G/LTE and 5G network, including LTE/EPC-based packet-data services and inter-operator roaming, citing the GSMA FS.20 specification for GTP security at the interconnect-facing network edge (paragraphs 119 and 120); and the '462 patent to its 4G/LTE and 5G network with IMS-based voice services, citing GSMA IMS standards and the GSMA NG.105 ENUM/IPX framework for identifying the service a terminating user is provisioned for (paragraphs 135 and 136).

What the complaint alleges

Each of the seven counts alleges direct infringement, induced infringement, and contributory infringement under 35 U.S.C. § 271(c). The complaint pleads knowledge at least as of the date of the complaint and, in the alternative, alleges on information and belief that the defendants were willfully blind through a policy of not reviewing the patents of others. In the count on the '436 patent, a footnote also alleges, in the alternative, knowledge of the '459 patent no later than July 7, 2018, through a patent issued to an AT&T affiliate that, the footnote says, cites the '459 patent family (paragraph 55, note 55). For the '462 patent, a footnote alleges, in the alternative, knowledge no later than May 18, 2018, through four patents issued to an AT&T affiliate between 2018 and 2020 that, the complaint says, cite the '462 patent family (paragraph 142, note 225). It says Session Link has complied with the marking statute and, on information and belief, that prior assignees and licensees did too.

Relief requested

The prayer asks for a judgment that the defendants directly infringed one or more claims of each patent, a permanent injunction under 35 U.S.C. § 283, damages no less than a reasonable royalty with interest and costs, and an exceptional case finding with attorney fees under § 285 (pages 168 and 169).

Where the case stands

Through November 4, 2026, the docket shows the complaint with the seven patents as exhibits, the patent and trademark form, the plaintiff's disclosure statement, notices of appearance, and a summons issued to all three defendants on November 3. Session Link Research filed three other patent suits in the Marshall Division the same day, Nos. 2:26-cv-00994, 2:26-cv-00995, and 2:26-cv-00996. Nos. 2:26-cv-00994 and 2:26-cv-00995 assert the same seven patents, and the '436 patent is the one patent asserted in No. 2:26-cv-00996. Watch for service on the defendants and their answers or motions. The case can end at any time, including by settlement or voluntary dismissal.