Patent Drafting Error? Claim Language Interpreted as Oft-Dreaded Means-Plus-Function Element

Intellectual Property Law

On August 28, the Federal Circuit issued its decision in Egenera, Inc. v. Cisco Systems, Inc.,1 offering a timely reminder of the importance of carefully drafting claim language as well as the technical specification that is used to interpret that claim language. A dispute over the interpretation of the claim language “logic to modify” ended in a Federal Circuit affirmation of a lower court decision holding that, because the technical specification did not disclose sufficient structure to perform the claimed modify function, the phrase should be considered an oft-dreaded “means plus function” element. Egenera had argued that the phrase “logic to modify” connoted generally software, firmware and/or circuitry to perform the modify function. However, the Federal Circuit considered the use of the claim term “logic” to merely recite generic black box structure that was purely a generic substitute for “means.”

The case began in August 2016, when Egenera, Inc. sued Cisco Systems, Inc. claiming that Cisco’s enterprise server systems infringed its U.S. Patent No. 7,231,430 (the ’430 patent).2

The ’430 patent was directed to a platform for automatically establishing a scalable and reconfigurable virtual network using software. It explained that the platform provided a significant collection of processors for the virtual network. A subgroup of the processors was configured as a virtual network for a specific group of applications or particular customers.3

Claim 1 recited the following:

1. A platform for automatically deploying at least one virtual processing area network, in response to software commands, said platform comprising:

a plurality of computer processors connected to an internal communication network;

at least one control node in communication with an external communication network and in communication with an external storage network having an external storage address space, wherein the at least one control node is connected to the internal communication network and thereby in communication with the plurality of computer processors, said at least one control node including logic to receive messages from the plurality of computer processors, wherein said received messages are addressed to the external communication network and to the external storage network and said at least one control node including logic to modify said received messages to transmit said modified messages to the external communication network and to the external storage network;

configuration logic for receiving and responding to said software commands, said software commands specifying (i) a number of processors for a virtual processing area network (ii) a virtual local area network topology defining interconnectivity and switching functionality among the specified processors of the virtual processing area network, and (iii) a virtual storage space for the virtual processing area network, said configuration logic including logic to select, under programmatic control, a corresponding set of computer processors from the plurality of computer processors, to program said corresponding set of computer processors and the internal communication network to establish the specified virtual local area network topology, and to program the at least one control node to define a virtual storage space for the virtual processing area network, said virtual storage space having a defined correspondence to a subset of the external storage address space of the external storage network; and

wherein the plurality of computer processors and the at least one control node include network emulation logic to emulate Ethernet functionality over the internal communication network.4

The “logic to modify” claim language within the control node modified outbound messages to be compatible with the destination/external network. Cisco argued before the district court that the “logic to modify” term should be construed as a means-plus-function element. The district court agreed and determined that the structure in the specification corresponding to the claimed “logic to modify” function was a virtual LAN proxy, a physical LAN driver and a virtual LAN server.5

Egenera appealed, challenging the interpretation of “logic to modify,” and the Federal Circuit affirmed the interpretation.

35 U.S.C. § 112(f) states:

An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.6

Claim language that employs the word “means” is presumed to invoke § 112(f), and claim language without the word “means” does not trigger the presumption. The circuit court said:

This presumption, however, does not permit patentees to freely engage in functional claiming while circumventing § 112(f) simply by avoiding the word “means,” . . . . And so the presumption against means-plus-function interpretation is rebuttable if a challenger demonstrates that a claim term either fails to recite sufficiently definite structure or recites function without reciting sufficient structure for performing that function. . . . [T]he presumption against means-plus-function claiming is not “strong” and that a challenger need not show that the limitation is essentially . . . devoid of anything that can be construed as structure. Rather, a challenger need only show that the structure is not sufficient. . . . For example, generic terms such as “mechanism,” “element,” “device,” and other . . . verbal constructs may be used in a claim in a manner that is tantamount to using the word means because they typically do not connote sufficiently definite structure and therefore may invoke § 112(f). . . . Such terms may amount to generic terms or black box recitations of structure or abstractions.7

If the presumption against the application of means-plus-function is disproved, the claimed function must be identified along with the structure, if any, that is disclosed in the specification corresponding to the claimed function.8

Egenera contended that the district court incorrectly interpreted “logic to modify” as a means-plus-function element in connection with the claim language of “logic to modify said received messages to transmit said modified messages to the external communication network and to the external storage network.”9

The district court said there was no corresponding structure disclosed in the specification. The court further observed that the specification disclosed that the logic to be implemented could be software logic or Basic Input/Output System (BIOS)-based. Egenera argued that logic meant the structure of software, firmware, circuitry, or one or more of those in combination. The district court disagreed, finding Egenera’s meaning was too broad and reflected just a generic black box for carrying out the computer-implemented functions. Accordingly, the district court determined that the presumption against means-plus-function claiming was rebutted.10

On appeal, Egenera asserted that “logic” was understood in the art to mean software, firmware, circuitry or some combination of them. Cisco contended, however, that “logic” meant only a general class of items that might perform the function. The Federal Circuit observed: 

The question is not whether a claim term recites any structure but whether it recites sufficient structure—a claim term is subject to § 112(f) if it recites function without reciting sufficient structure for performing that function. . . . Egenera does not explain how its “logic”—even assuming it connotes some possible structure in the general sense of software, firmware, or circuitry—amounts to sufficient structure for performing [the modification] function.11

Egenera also asserted that based on the claim language, logic connoted structure because the “logic to modify” was part of the claimed “control node.” The Federal Circuit disagreed and explained that was not enough. According to the court:

Mere inclusion of a limitation within a structure does not automatically render the limitation itself sufficiently structural. And, again, the question is not whether “logic” is utterly devoid of structure but whether the claim term recites sufficient structure to perform the claimed functions.12

Therefore, the Federal Circuit agreed with Cisco that

§ 112(f) applies here. As used, “logic” is no more than a “black box recitation of structure” that is simply a generic substitute for “means.” . . . We therefore conclude that Cisco overcame the presumption against applying § 112(f).13

Takeaways:

Means-plus-function claims create significant uncertainty regarding the scope of the claims when employed, which in some ways is ironic because the statute was supposed to endorse such a claim technique and provide additional clarity by incorporating the corresponding structure performing the function as part of the claim interpretation. The Federal Circuit has added to this uncertainty by considering claim language that does not directly employ the use of the word “means” as a means-plus-function element with the creation of a “not strong” rebuttable presumption.

Not certain why this is important? It’s not an unreasonable question in view of the complexity of patent claims. Patent claims are to inventions as property boundaries are to real estate. If you have an incorrect description of your property boundaries, you could end up with less property. The same applies to an invention—an incorrect claim description can result in an unnecessarily narrow or limited invention.

Ask yourself (if you are still reading): Would the decision have been different if the claim was slightly changed to read as follows?

wherein said received messages are addressed to the external communication network and to the external storage network and said at least one control node including logic to modifying said received messages to transmit said modified messages to the external communication network and to the external storage network;

This revised language has the control node directly performing the modify function. If a control node is not sufficient structure, what structure would be sufficient for a computer software-related invention? A computer processor? Has the Federal Circuit unknowingly increased the application of means-plus-function language?

Didn’t the Court of Customs and Patent Appeals (CCP), the predecessor court to the Federal Circuit that is considered as an en banc court, hold a while ago in 1971, after 35 U.S.C. § 112(f) codified means-plus-function language, that functional language is not impermissible and can be clear without invoking § 112(f)?

We take the characterization “functional” . . . to indicate nothing more than the fact that an attempt is being made to define something (in this case, a composition) by what it does rather than by what it is (as evidenced by specific structure or material, for example). In our view, there is nothing intrinsically wrong with the use of such a technique in drafting patent claims. Indeed we have even recognized in the past the practical necessity for the use of functional language.14

Does the Federal Circuit’s decision “put the cart before the horse” by reviewing the specification to determine whether the claim language is means plus function (as opposed to reviewing the claim language itself)?

In the end, claims are interpreted in view of the specification. Accordingly, a specification that describes software and hardware implementation details is more likely to reduce unintended claim interpretation meanings. Thus, patent applicants would be wise to draft technical details, including software design/architecture and software functionality associated at least with the inventive features and functionality, and preferably any technical and software details that one of ordinary skill would consider important in understanding the invention. The decision serves as notice to patent applicants that failing to include detailed descriptions of software and hardware implementation information can result in an unintended claim interpretation.


Irah Donner is a partner in Manatt’s intellectual property practice and is the author of Patent Prosecution: Law, Practice, and Procedure, Eleventh Edition, and Constructing and Deconstructing Patents, Second Edition, both published by Bloomberg Law. Irah was also a software developer and former Member of Technical Staff at Bell Communications Research (Bellcore).


1 Egenera, Inc. v. Cisco Systems, Inc., 972 F.3d 1367, 2020 USPQ2d 10997, 2020 WL 5084288 (Fed. Cir. 2020).

2 Id., 972 F.3d at 1369.

3 Id., 972 F.3d at 1370.

4 Id., 972 F.3d at 1370-71 (quoting U.S. Patent No. 7,231,430, claim 1) (emphasis added).

5 Id., 972 F.3d at 1371-72.

6 Id., 972 F.3d at 1372 (quoting 35 U.S.C. § 112(f)).

7 Id., 972 F.3d at 1373 (quoting Williamson v. Citrix Online LLC, 792 F.3d 1339, 1350, 115 USPQ2d 1105, 1112 (Fed. Cir. 2015) and MTD Prods. Inc. v. Iancu, 933 F.3d 1336, 1341, 2019 USPQ 298144, at *4 (Fed. Cir. 2019)) (quotation marks omitted).

8 Id., 972 F.3d at 1373 (quoting Williamson v. Citrix Online LLC, 792 F.3d 1339, 1351, 115 USPQ2d 1105, 1113 (Fed. Cir. 2015)) (quotation marks omitted).

9 Id., 972 F.3d at 1373.

10 Id., 972 F.3d at 1373-74.

11 Id., 972 F.3d at 1374 (quoting Williamson v. Citrix Online LLC, 792 F.3d 1339, 1348, 115 USPQ2d 1105, 1111 (Fed. Cir. 2015)) (emphasis added by court) (quotation marks omitted).

12 Id., 972 F.3d at 1374.

13 Id., 972 F.3d at 1374 (citing Williamson v. Citrix Online LLC, 792 F.3d 1339, 1350, 115 USPQ2d 1105, 1112 (Fed. Cir. 2015)).

14 In re Swinehart, 439 F.2d 210, 169 USPQ 226, 228-29 (C.C.P.A. 1971) (emphasis added).

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