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Covad Does Not Infringe Bell Atlantic’s ADSL Patent

August 17, 2001

Decision icon Decision

Last Month at the Federal Circuit - September 2001

Judges: Gajarsa (author), Lourie, and Plager

In Bell Atlantic Network Services, Inc. v. Covad Communications Group, Inc., No. 00- 1475 (Fed. Cir. Aug. 17, 2001), the Federal Circuit affirmed a district court’s grant of SJ that Covad Communications Group, Inc.; Dieca Communications, Inc.; and Covad Communications Company (collectively “Covad”) did not infringe Bell Atlantic Networks Services, Inc.’s (“Bell Atlantic”) U.S. Patent No. 5,812,786 (“the ‘786 patent”).

The ‘786 patent relates to digital subscriber line (“DSL”) technology, which allows a regular telephone line to be used as a highspeed, multichannel data delivery system. Through a technique known as “frequency division multiplexing,” the transceivers enable regular telephone lines to carry both regular, low-speed voice data as well as higher speed digital communications. Symmetric DSL (“SDSL”) uses a range of frequencies as a single two-way channel, transmitting and receiving data on the channel at the same rate, whereas asymmetric DSL (“ADSL”) allocates different amounts of bandwidth based on customer

The ‘786 patent discloses and claims a data transmission system that provides DSL service with variable rates and modes using existing hardware and equipment. In particular, the claimed invention improved existing DSL technology by providing an ADSL system with adjustable variable rate functionality, i.e., the system could controllably increase the data rate of a channel to permit operation in an optimum mode at an optimum rate for the customer’s chosen function.

The district court had granted Covad’s motion for SJ of noninfringement based on its construction of the following terms from the asserted independent claims 1 and 21: “the plurality of different modes,” ”ADSL/AVR transceiver,” first and second “channels,” and “selectively changing [the] transmission rates.” Once apprised of the district court’s claim construction, Bell Atlantic conceded literal infringement. The district court ruled in favor of Covad with respect to the DOE.

Relying exclusively on the intrinsic evidence, the Federal Circuit affirmed the district court’s conclusion that “the plurality of different modes” and “ADSL/AVR transceiver” limitations restricted the claimed invention to only the three types of modes of operation described in the specification, specifically, data transfer modes. Bell Atlantic argued that different “modes” could include different data transfer rates, as well as different directional operations such as conventional, bidirectional, and reversible. Rejecting Bell Atlantic’s argument that the claim language’s ordinary meaning should control, the Federal Circuit focused instead on the meaning the specification imparted to the word “mode.” Carefully parsing all portions of the patent, the Federal Circuit concluded that the patentees had defined the term “mode” by implication through consistent use of that term throughout the ‘786 patent specification. In this situation, the Federal Circuit concluded that the specification compelled restricting the claim to the described three modes of channel direction operation, explaining that the usage “preferred” does not of itself broaden the claims beyond their support in the specification. The Federal Circuit also considered the prosecution arguments made by Bell Atlantic to explain away a prior art reference to support its affirmance.

Turning to the “channel” limitation, the Federal Circuit agreed with Bell Atlantic that the district court had erred in construing “channel” as “an amount of bandwidth isolated for communications that may be either unidirectional or bi-directional.” Rather, the intrinsic evidence, particularly the claim language and the specification, make clear that the word “channel” encompasses only oneway communication. Contrary to Covad’s suggestion, the specification’s multiple references to bidirectional channels did not mandate a broader construction since those statements were made with reference to the prior art.

The Federal Circuit, however, agreed with the district court that the claimed “channels” are separated by frequency. Although the Federal Circuit acknowledged that the ordinary meaning of the word “channel” is quite broad, the district court’s narrower interpretation was justified because the only type of channels contemplated by the ‘786 patent are those that occupy an amount of bandwidth and are separated in frequency.

Finally, the Federal Circuit rejected Covad’s challenge to the district court’s construction of the “selectively changing” claim language as meaning a change is chosen and occurs, although it need not occur during a communication session. According to Covad, the limitation required a change during a communication session.

The Federal Circuit first dealt with Bell Atlantic’s jurisdictional challenge to Covad’s argument. Relying on the general rule that a prevailing party may present any argument that supports the judgment in its favor without taking a cross appeal, the Court sided with Covad, explaining that it could entertain Covad’s challenge despite Covad’s failure to file a cross appeal.

As to the merits, however, the Court concluded that notwithstanding that the specification discloses changing the transmission mode and rate during a communication session, the specification expressly stated that the mode and rate could be changed at times other than during a communication session. Such a varied use of a limitation throughout a patent specification demonstrates breadth rather than restriction, the Court reasoned.

The Federal Circuit then affirmed the district court’s finding of noninfringement under the DOE. According to Bell Atlantic, evidence in the record established that Covad’s single bidirectional SDSL linecards were insubstantially different from the two unidirectional channels described in the ‘786 patent. Without examining the alleged evidence, the Federal Circuit concluded that affirmance was mandated under the “all elements rule,” which requires that every element (or its equivalent) of a claim must be found in the accused device. Specifically, Bell Atlantic’s theory of equivalent infringement would entirely vitiate the claim limitations that require the transceivers to “selectively change” the rate or mode of operation and the limitations that require two unidirectional channels separated by frequency.