Claim 1 of 5,862,312 defined a network as "interconnecting each one of said processor systems in a point-to-point two way channel interconnection with each other one of said processor systems". Claim 37 was broader, leaving out the "point-to-point" limitation: "interconnecting each one of said processor systems through a network for data communications with each other one of said processor systems". Seachange sued C-COR for infringement of claim 37, but not claim 1. As the CAFC observed:

Claim 37 does not suggest that the claimed “network” is limited to networks employing direct, point-to-point interconnections. The language specifies only that each processor system be interconnected to each other processor system. Moreover, the technical dictionary definition of “network” does not suggest the point-to-point limitation; indeed, it implies that a “network for data communications” can employ direct or indirect interconnections. See The New IEEE Standard Dictionary of Electrical and Electronics Terms 842 (5th ed. 1993) (hereinafter “IEEE”).

Seachange agrees with this assessment and asks that we apply the doctrine of claim differentiation. The doctrine of claim differentiation stems from “the common sense notion that different words or phrases used in separate claims are presumed to indicate that the claims have different meanings and scope.” Karlin Tech. Inc. v. Surgical Dynamics, Inc., 177 F.3d 968, 971-72 (Fed. Cir. 1999). Although the doctrine is at its strongest “where the limitation sought to be ‘read into’ an independent claim already appears in a dependent claim,” Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 910 (Fed. Cir. 2004), there is still a presumption that two independent claims have different scope when different words or phrases are used in those claims, Kraft Foods, Inc. v. Int’l Trading Co., 203 F.3d 1362, 1365-69 (Fed. Cir. 2000); see also Tandon Corp. v. U.S. Int’l Trade Comm’n, 831 F.2d 1017, 1023 (Fed. Cir. 1987). However, the doctrine “only creates a presumption that each claim in a patent has a different scope; it is not a hard and fast rule of construction.” Kraft, 203 F.3d at 1368 (internal quotations omitted). “[T]he doctrine of claim differentiation can not broaden claims beyond their correct scope, determined in light of the specification and the prosecution history and any relevant extrinsic evidence. . . . [C]laims that are written in different words may ultimately cover substantially the same subject matter.” Multiform Desiccants, Inc. v. Medzam, Ltd., 133 F.3d 1473, 1480 (Fed. Cir. 1998).

So, the daylight for non-infringement that C-COR sought, but was denied by the district court, was that claim 37 was essentially the same as claim 1 ("different words may ultimately cover substantially the same subject matter"), "in light of the specification and the prosecution history and any relevant extrinsic evidence".

C-COR argued that both the specification and the prosecution history directed that claim 37 be limited to point-to-point interconnection. The CAFC didn't bite on the specification argument, finding the evidence inconclusive - that the point-to-point embodiment might reasonably be considered exemplary, not necessarily limiting.

During prosecution, the Examiner rejected claims based upon a 103(a) prior art combination. The prosecuting attorney overcame the rejections by arguing that the prior art did not disclose a network of point-to-point communications. Further, oddly, there was a protest by a third party after the claims were initially allowed, and the prosecutor made the same point-to-point argument again to regain allowance.

The CAFC properly corked Seachange's claim construction weaseling.

C-COR argues that Applicant’s arguments made during prosecution narrowed the scope of the “network for data communications” limitation in claim 37 (40) to cover only a point-to-point network. Seachange counters that Applicant’s arguments did not amount to a clear and unambiguous disclaimer of claim scope. We agree with C-COR.

“The prosecution history constitutes a public record of the patentee’s representations concerning the scope and meaning of the claims, and competitors are entitled to rely on those representations when ascertaining the degree of lawful conduct, such as designing around the claimed invention.” Hockerson-Halberstadt, Inc. v. Avia Group Int’l, Inc., 222 F.3d 951, 957 (Fed. Cir. 2000). Thus, in construing the claim, we consider the prosecution history to determine “whether the patentee disclaimed or disavowed subject matter, narrowing the scope of the claim terms.” Nystrom v. Trex Co., 374 F.3d 1105, 1113 (Fed. Cir. 2004) (internal quotation omitted). In doing so, we examine the entire prosecution history, which includes amendments to claims and all arguments to overcome and distinguish references. Rheox, Inc. v. Entact, Inc., 276 F.3d 1319, 1326 (Fed. Cir. 2002); Elkay Mfg. Co. v. Ebco Mfg. Co., 192 F.3d 973, 979 (Fed. Cir. 1999). Where an applicant argues that a claim possesses a feature that the prior art does not possess in order to overcome a prior art rejection, the argument may serve to narrow the scope of otherwise broad claim language. Rheox, Inc., 276 F.3d at 1325 (“Explicit arguments made during prosecution to overcome prior art can lead to narrow claim interpretations . . . .”); Ekchian v. Home Depot, Inc., 104 F.3d 1299, 1304 (Fed. Cir. 1997) (“[S]ince, by distinguishing the claimed invention over the prior art, an applicant is indicating what the claims do not cover, he is by implication surrendering such protection.”). A disclaimer must be clear and unambiguous. Omega Eng’g, Inc. v. Raytek Corp., 334 F.3d 1314, 1323-25 (Fed. Cir. 2003).