262 F.3d 1258 (Fed. Cir. 2001)
BELL ATLANTIC NETWORK SERVICES, INC. (doing business as Verizon Services, Inc.),Plaintiff-Appellant,v.COVAD COMMUNICATIONS GROUP, INC., DIECA COMMUNICATIONS, INC. (doing business as COVAD Communications Company), and COVAD COMMUNICATIONS COMPANY, INC., Defendants-Appellees.
00-1475
United States Court of Appeals for the Federal Circuit
August 17, 2001

Appealed from: United  States  District  Court  for  the  Eastern District of Virginia  Judge Jerome B. Friedman [Copyrighted Material Omitted][Copyrighted Material Omitted][Copyrighted Material Omitted]
Richard G. Taranto, Farr & Taranto, of Washington, DC, argued for plaintiff-appellant. Of counsel on the brief were George C. Lombardi, and James F. Hurst, Winston & Strawn, of Chicago, Illinois; Adam T. Bernstein, Verizon Communications, of New York, New York; and John Thorne, Verizon Services, Inc., of Arlington, Virginia.
Ruffin B. Cordell, Fish & Richardson P.C., of Washington, DC, argued for defendants-appellees. With him on the brief were Michael J. McKeon, and Lauren A. Degnan.
Before LOURIE, Circuit Judge, PLAGER, Senior Circuit Judge, and GAJARSA, Circuit Judge.
GAJARSA, Circuit Judge.


1
Bell Atlantic Network Services, Inc. ("Bell Atlantic") is the owner of  United States Patent No. 5,812,786 ("the '786 patent"), which concerns  certain data transmission services, particularly certain digital subscriber  line ("DSL") services.1 In 1999, Bell Atlantic brought this  patent infringement action against Covad Communications Company, Inc.,  DIECA Communications, Inc., and Covad Communications Group, Inc. (collectively "Covad"), alleging that certain DSL services offered by Covad  infringe the '786 patent. On April 4, 2000, the United States District  Court for the Eastern District of Virginia ("district court") determined  that certain limitations required by claims 1 and 21 of the '786 patent are  not present in Covad's DSL systems either literally or under the doctrine  of equivalents, and granted Covad's motion for summary judgment of  noninfringement. Bell Atlantic Network Servs. v. Covad Communications  Group, Inc., 92 F.Supp.2d 438 (E.D.Va. 2000).  Bell  Atlantic appeals that judgment.


2
For the reasons discussed below, we affirm.

I. BACKGROUND
A. Introduction

3
DSL technology is a relatively new data transfer technology that can turn a  single pair of copper telephone wires ("a copper pair") into a high-speed,  multi-channel, data delivery system. A basic DSL system consists of two  high-speed modems located at each end of a conventional telephone line- one  at the telephone company's end, and one at the customer's end. This  technology allows customers to gain high-speed access to large sources of  data, including the internet, without the need for expensive additional  wiring.


4
Prior to the advent of DSL technology, copper telephone wiring transmitted  simple voice data at frequencies below four kilohertz (4 kHz). The  transmission of this common residential telephone service is known as  "POTS" ("Plain Old Telephone Service"). It has been known for some time  that additional communications streams can be carried on the same wire with  POTS through a technique called "frequency division multiplexing."  Frequency division multiplexing is a scheme in which numerous signals are  combined for transmission on a single communications line by assigning each  signal a different frequency. Until recently, much of the available range  of frequencies, or "bandwidth," on twisted-pair copper telephone wiring  remained unused. DSL technology enables high-speed transmissions over  common copper telephone wiring by exploiting the unused, higher frequencies  over twisted-pair wires.


5
In order to take advantage of the higher frequencies, DSL technology  employs high-speed modems, or transceivers, to modulate and demodulate the  high-frequency data. The transceivers allow the low frequencies to be used  for traditional POTS communication, while simultaneously using the higher  frequencies for high-speed digital communications. A transceiver must be  employed at each end of the "subscriber loop"- the customer's end and the  telephone company's switching office.


6
Currently, there are two major types of DSL technology. Symmetric or  single-line digital subscriber line ("SDSL") technology uses a range of  frequencies as a single two-way channel, and transmits and receives data on  this channel at the same rate. Asymmetric digital subscriber line ("ADSL")  technology allocates different amounts of bandwidth based on the needs of  the customer. SDSL technology may be more suitable for videoconferencing  applications, because equal upstream and downstream data transmission rates  are preferable. However, ADSL technology may be more suitable for video-on-  demand services and for customers who download more data in the  "downstream" direction than they upload in the "upstream" direction.  Traditionally, ADSL systems have allocated more bandwidth for downstream  communication than for upstream communication. Indeed, prior art ADSL  systems allocate only a small amount of bandwidth (approximately 15 kHz) to  the upstream channel, also referred to as the "control" channel.


7
Figure 4 of the '786 patent specification illustrates how conventional ADSL  systems have divided common telephone lines into different channels using  frequency division multiplexing: [Tabular or Graphical Material Omitted]


8
The diagram illustrates that in prior art ADSL systems, POTS service uses  only 4 kHz, the control channel uses about 15 kHz, and the downstream data  channel uses most of the remaining bandwidth.

B. The '786 Patent Claims

9
The invention disclosed by the '786 patent concerns data transmission  systems that can be used to provide DSL services with variable rates and  modes without replacing the underlying hardware and equipment. The written  description of the '786 patent notes that prior art ADSL systems were "not  well suited for other services in which the nature and amount of data and  control signal transfer is substantially different and changes frequently."  '786 patent, col. 2, ll. 26-28. The specification observes that "the two-  way control channel may be unacceptably slow for services such as  interactive multi-media, distance learning, or accessing a server in a  remote local area network (LAN) over a POTS line using a single copper  pair. One or more of these services may require a bi-directional control  channel of up to, for example, 384 kbps [kilobits per second] in order to  allow substantially real-time communications so that a subscriber is not  waiting for information to be transmitted." Id. at col. 2, ll. 29-36.


10
Thus, the invention disclosed by the '786 patent adds capabilities to  current DSL technology by providing an ADSL system with "adjustable  variable rate" functionality ("ADSL/AVR"). The '786 patent notes in the  Summary of the Invention that "such a network has the advantages of  conventional ADSLs, while allowing the data rate of the reverse control  signaling channel to be controllably increased so as to have a higher rate  transmission than ADSL in a bi-directional mode." Id. at col. 3, ll. 15-19.  In other words, the ADSL system described by the '786 patent allows  customers to "access any file server, download files, store information,  and perform any other functions permitted in the optimum mode and at the  optimum rate for that function." Id. at col. 15, ll. 7-9.


11
Claims 1 and 21 are the two independent claims at issue in this appeal.  The claims read as follows: 1.A transmission system for variably transmitting information data in a plurality of different modes over a network, said transmission system comprising:


12
a first transceiver, connected to a first end of a subscriber loop, for selectively operating in one of said plurality of different modes, said first transceiver transmitting or receiving signals, at a first transmission rate, on a first channel, and transmitting or receiving signals, at a second transmission rate, on a second channel, in each of said plurality of different modes;


13
a second transceiver, connected to said first transceiver via said subscriber loop, for selectively operating in one of said plurality of different modes, said second transceiver transmitting or receiving said first channel signals at said first transmission rate on said first channel and transmitting or receiving said second channel signals at said second transmission rate on said second channel; and


14
a controller connected to said first transceiver for selectively changing said first and second transmission rates.


15
21.An ADSL/AVR transmission system for variably transmitting information data over a plurality of channels, comprising:


16
a first ADSL/AVR transceiver for transmitting or receiving signals at a first transmission rate on a first channel, and transmitting or receiving signals at a second transmission rate on a second channel;


17
a second ADSL/AVR transceiver for transmitting or receiving signals at said first transmission rate on said first channel and transmitting or receiving said second channel signals at said second transmission rate on said second channel; and


18
a subscriber loop for connecting said first and second ADSL/AVR transceivers together; wherein


19
each of said first and second ADSL/AVR transceivers includes a controller for selectively changing the transmission rates on said first and second channels.


20
Id. at col. 17, ll. 5-23; col. 19, ll. 27-44 (emphasis added).

C. The Accused Covad DSL System

21
Covad provides its customers with both ADSL and SDSL services. Covad also  uses DSL transceivers, called "line cards," at both ends of the subscriber  loop. In Covad's ADSL line card transceivers, the allocation of bandwidth  between the upstream and downstream channels is fixed, with most of the  frequency allocated to the downstream channel. Because the bandwidth  allocation is fixed, Covad's ADSL line card transceivers are incapable of  shifting bandwidth between the upstream and downstream channels without  removing and reprogramming the line card transceivers. In Covad's SDSL  line card transceivers, the allocation of bandwidth to the single, two-way  SDSL channel is also fixed. Covad's SDSL line card transceivers use "echo  cancellation" techniques to allow two-way communication within the single  SDSL frequency range.2

D. Procedural Background

22
On January 20, 2000, Covad filed a motion for summary judgment of  noninfringement based on its proposed claim construction of three  limitations contained in the '786 patent. On February 11, 2000, prior to  the close of discovery, the district court conducted a hearing in which the  parties discussed the technology and claims of the '786 patent. On February  18, 2000, the district court informed the parties that it would grant  Covad's motion for summary judgment of noninfringement. On April 4, 2000,  the district court issued its opinion and order explaining its claim  constructions, and granting summary judgment of noninfringement in favor of  Covad.


23
The district court's grant of summary judgment of noninfringement was based  on the construction of three limitations contained in claims 1 and 21: (1)  the "plurality of different modes" limitation in claim 1 and the "ADSL/AVR  transceiver" limitation in claim 21; (2) the first and second "channel"  limitation in both claims; and (3) the "selectively changing [the]  transmission rates" limitation in both claims. '786 patent, col. 17, ll. 5-  23; col. 19, ll. 27-44.


24
The district court construed the first limitation to require the  transceiver described in both claims 1 and 21 to be:


25
[A] transceiver that operates by dividing available bandwidth between two channels in at least two of the following ways, (1) where the first channel is smaller than the second ("conventional ADSL" mode); (2) where the two channels are of "roughly" equal size ("bi- directional" mode); and (3) where the first channel is larger than the second ("reversible" mode).


26
Bell Atlantic, at 491. The district court relied  exclusively on the intrinsic evidence, including the claims, the written  description, and the prosecution history, in arriving at its construction.  It observed that, throughout the specification, the written description  describes only these three possible modes. It concluded that it would "not  broaden claims 1 and 21 beyond their support in the specification, as the  three modes discussed in the patent specification literally occupy the  field of possibilities contemplated by the '786 patent." Id. At 494.


27
The district court also relied solely on the intrinsic evidence for its  construction of the first and second "channels" limitation. Based on a  reading of the written description, the district court construed the first  and second "channels" to mean: "An amount of bandwidth isolated for  communications that may be either unidirectional or bi-directional." Id. at  495. Finally, it construed the "selectively changing" limitation to mean  that "a change [in transmission rates] is chosen and occurs, although it  need not occur during a communication session."  Id. at 497. Based on these  claim constructions, Bell Atlantic conceded that the accused Covad systems  do not literally infringe. Moreover, the district court determined that  Covad's SDSL transceivers do not infringe under the doctrine of equivalents  because they "perform substantially different functions in a substantially  different way to achieve substantially different results."  Id. at 498. The  district court reasoned that "Covad's single channel utilizes echo  cancellation techniques to allow two-way communications, which differs  substantially from two separate unidirectional channels."  Id. at 497.


28
Bell Atlantic timely appealed to this court. We have jurisdiction pursuant  to 28 U.S.C. § 1295(a)(1) (1994).

II. STANDARD OF REVIEW

29
We review the grant of a motion for summary judgment de novo, drawing all  reasonable inferences in favor of the non-moving party. Anderson v. Liberty  Lobby, Inc., 477 U.S. 242, 255 (1986). Summary judgment "shall be rendered  forthwith if the pleadings, depositions, answers to interrogatories, and  admissions on file, together with the affidavits, if any, show that there is no genuine issue as to any material fact and that the moving party is  entitled to a judgment as a matter of law." Fed. R. Civ. P. 56(c); Newbanks  v. Cent. Gulf Lines, Inc., 64 F. Supp. 2d 1, 4 (D. Mass. 1999).


30
The determination of infringement is a two-step process. First, the court  construes the claims to correctly determine the scope of the claims.  Second, it compares the properly construed claims to the accused device.  Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448, 1454, 46 USPQ2d 1169, 1172  (Fed. Cir. 1998) (en banc). Claim construction is an issue of law that we  review de novo. Markman v. Westview Instruments, Inc., 52 F.3d 967, 970-71,  34 USPQ2d 1321, 1322 (Fed. Cir. 1995) (en banc), aff'd, 517 U.S. 370  (1996); Cybor, 138 F.3d at 1456, 46 USPQ2d at 1172.


31
A determination of infringement, both literal and under the doctrine of  equivalents, is a question of fact. Insituform Techs., Inc. v. CAT  Contracting, Inc., 161 F.3d 688, 692, 48 USPQ2d 1610, 1614 (Fed. Cir.  1998). Thus, viewing the facts and inferences in the light most favorable  to Bell Atlantic, summary judgment is proper only if "no reasonable jury  could return a verdict for the nonmoving party." Anderson, 477 U.S. at 255 .  The determination of infringement under the doctrine of equivalents is  limited by two primary legal doctrines: (1) prosecution history estoppel  and (2) the "all elements" rule. Festo Corp. v. Shoketsu Kinzoku Kogyo  Kabushiki Co., 234 F.3d 558, 586, 56 USPQ2d 1865, 1886 (Fed. Cir. 2000) (en  banc), cert. granted, 69 U.S.L.W. 3673 (U.S. June 18, 2001) (No. 00-1543).  The application of these legal limitations is reviewed by this court de  novo. Id.

III. DISCUSSION
A.   Claim Construction

32
"It is well-settled that, in interpreting an asserted claim, the court  should look first to the intrinsic evidence of record, i.e., the patent  itself, including the claims, the specification and, if in evidence, the  prosecution history . . . . Such intrinsic evidence is the most significant  source of the legally operative meaning of disputed claim language."  Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582, 39 USPQ2d 1573,  1576 (Fed. Cir. 1996).


33
We look first to the claim language itself to define the scope of the  patented invention. Id. As a starting point, we give claim terms their  ordinary and accustomed meaning as understood by one of ordinary skill in  the art. Hockerson-Halberstadt, Inc. v. Avia Group Int'l, Inc., 222 F.3d  951, 955, 55 USPQ2d 1487, 1490 (Fed. Cir. 2000). Accordingly, a technical  term used in a patent is interpreted as having the meaning a person of  ordinary skill in the field of the invention would understand it to mean.  Interactive Gift Express, Inc. v. Compuserve Inc., 2001 WL 792669, *7 (Fed.  Cir. July 13, 2001).


34
Dictionaries and technical treatises, which are extrinsic evidence, hold a  "special place" and may sometimes be considered along with the intrinsic  evidence when determining the ordinary meaning of claim terms. Vitronics,  90 F.3d at 1584 n.6, 39 USPQ2d at 1577 n.6. Furthermore, we have previously  cautioned against the use of non-scientific dictionaries "lest dictionary  definitions . . . be converted into technical terms of art having legal,  not linguistic significance."  Multiform Desiccants, Inc. v. Medzam, Ltd.,  133 F.3d 1473, 1478, 45 USPQ2d 1429, 1433 (Fed.Cir.1998).


35
Generally, there is a "heavy presumption" in favor of the ordinary meaning  of claim language as understood by one of ordinary skill in the art.  Johnson Worldwide Assocs., Inc. v. Zebco Corp., 175 F.3d 985, 989, 50  USPQ2d 1607, 1610 (Fed. Cir. 1999). This presumption is overcome:  (1) where the patentee has chosen to be his own lexicographer, or (2) where  a claim term deprives the claim of clarity such that there is "no means by  which the scope of the claim may be ascertained from the language used."  Id. at 990, 50 USPQ2d at 1610. In the first situation, a patentee may  choose to be his own lexicographer and use terms in a manner other than  their ordinary meaning. Vitronics, 90 F.3d at 1582, 39 USPQ2d at 1576.  Therefore, the court must examine the intrinsic evidence to determine  whether the patentees have given the term an unconventional meaning.  Hockerson, 222 F.3d at 955, 55 USPQ2d at 1490. The specification acts as a  dictionary "when it expressly defines terms used in the claims or when it  defines terms by implication." Vitronics, 90 F.3d at 1582, 39 USPQ2d at  1577. "Thus, the specification is always highly relevant to the claim  construction analysis. Usually, it is dispositive; it is the single best  guide to the meaning of a disputed term." Id.


36
We have previously held that, in redefining the meaning of particular claim  terms away from the ordinary meaning, the intrinsic evidence must "clearly  set forth" or "clearly redefine" a claim term so as to put one reasonably  skilled in the art on notice that the patentee intended to so redefine the  claim term. Elektra Instr. v. O.U.R. Scientific Int'l, 214 F.3d 1302, 1307,  54 USPQ2d 1910, 1913 (Fed. Cir. 2000); N. Telecom v. Samsung, 215 F.3d  1281, 1287, 55 USPQ2d 1065, 1069 (Fed. Cir. 2000). We have also stated that  the specification must exhibit an "express intent to impart a novel  meaning" to claim terms. Schering v. Amgen, 222 F.3d 1347, 1353, 55 USPQ2d  1650, 1654 (Fed. Cir. 2000); Optical Disc v. Del Mar Avionics, 208 F.3d  1324, 1334, 54 USPQ2d 1289, 1295 (Fed. Cir. 2000). However, a claim term  may be clearly redefined without an explicit statement of redefinition.  Indeed, we have specifically held that the written description of the  preferred embodiments "can provide guidance as to the meaning of the  claims, thereby dictating the manner in which the claims are to be  construed, even if the guidance is not provided in explicit definitional  format."  Scimed Life Sys., Inc. v. Advanced Cardiovascular Sys., Inc., 242  F.3d 1337, 1344, 58 USPQ2d 1059, 1065 (Fed. Cir. 2001). In other words, the  specification may define claim terms "by implication" such that the meaning  may be "found in or ascertained by a reading of the patent documents."  Vitronics, 90 F.3d at 1582, 1584 n.6, 39 USPQ2d at 1577, 1578 n.6.


37
Moreover, we must also examine the prosecution history to determine whether  the patentee has relinquished a potential claim construction in an  amendment to the claim or in an argument to overcome or distinguish a  reference. Southwall Techs., Inc. v. Cardinal IG, Co., 54 F.3d 1570, 1576,  34 USPQ2d 1673, 1676 (Fed. Cir. 1995); Interactive Gift, 256 F.3d 1323, 1331. This history contains the complete record of all the proceedings before  the Patent and Trademark Office, including any express representations made  by the applicant regarding the scope of the claims.  Vitronics, 90 F.3d at  1582, 39 USPQ2d at 1577. The prosecution history is considered to determine  whether or not there were any express representations made in obtaining the  patent regarding the scope and meaning of the claims. Id.


38
Finally, if the meaning of the claim limitation is apparent from the  intrinsic evidence alone, it is improper to rely on extrinsic evidence  other than thatused to ascertain the ordinary meaning of the claim  limitation.  Id. However, in the rare circumstance that the court is unable  to determine the meaning of the asserted claims after assessing the  intrinsic evidence, it may look to additional evidence that is extrinsic to  the complete document record to help resolve any lack of clarity. Id. at  1584, 90 F.3d 1576, 39 USPQ2d at 1578. This additional extrinsic evidence includes such  evidence as expert testimony, articles, and inventor testimony. Id. This  extrinsic evidence may be used only to assist in the proper understanding  of the disputed limitation; it may not be used to vary, contradict, expand,  or limit the claim language from how it is defined, even by implication, in  the specification or file history. Id. at 1584-85, 39 USPQ2d at 1579.


39
1.The "Plurality of Different Modes" and "ADSL/AVR" Limitations


40
Bell Atlantic challenges the district court's claim construction of the  "plurality of different modes" limitation in claim 1 and the "ADSL/AVR  transceiver" limitation in claim 21. Based on the ordinary meaning of the  word "mode," Bell Atlantic argues that the phrase "plurality of different  modes" simply requires "multiple operational states providing different  transmission services, as distinguished by their upstream and downstream  transmission rates, whether the differences are achieved by altering  bandwidth or by the other familiar methods of altering transmission rates."  Bell Atlantic argues that the universe of "modes" contemplated by the '786  patent is not limited to the three modes discussed by the district court  (conventional, bi-directional, and reversible). Bell Atlantic reasons that  these three modes are simply "three broad categories" that may encompass  other operational "modes." Specifically, Bell Atlantic contends that the  rate of data transfer (as opposed to the bandwidth) within each of the  three broad categories can be changed to create additional modes.


41
For example, Bell Atlantic posits that a bi-directional service "offering  192 Kbps [kilobits per second] in each direction is quite different from  one offering 1.1 Mbps [megabits per second]." Under the district court's  construction, both services would operate in the same "mode" (bi-  directional) because both services allocate the same amount of bandwidth to  both the upstream and downstream directions. However, Bell Atlantic argues  that the 192 Kbps bi-directional service would operate in a different  "mode" than the 1.1 Mbps bi-directional service because the rate of data  transmission varies between the two services. Bell Atlantic also suggests  that a transmission system may be changed from a conventional ADSL mode to  a bi-directional mode by increasing the coding to allow "more bits per  baud" or by "bit stuffing" without altering the relative bandwidth  distribution of the upstream and downstream channels. In short, Bell  Atlantic argues that "a plurality of different modes" also encompasses  different methods of altering the transmission rates within the three broad  categories.


42
It may be true that the ordinary meaning of the word "mode" supports a  broader meaning than the construction ascertained by the district court.  However, we must look at the intrinsic evidence to determine whether the  patentee has given the term an unconventional meaning. Hockerson, 222 F.3d  at 955, 55 USPQ2d at 1490; Vitronics, 90 F.3d at 1582, 39 USPQ2d at 1576.  We are mindful that the patentee may act as his own lexicographer by using  the specification to define terms either expressly or "by implication."   Vitronics, 90 F.3d at 1582, 39 USPQ2d at 1577. Moreover, the ordinary  meaning of the non-technical term "mode" is sufficiently broad and  amorphous that the scope of the claim language can be reconciled only with  recourse to the written description. Comark Communications, Inc. v. Harris  Corp., 156 F.3d 1182, 1187, 48 USPQ2d 1001, 1005 (Fed. Cir. 1998).


43
a.   The '786 Patent Specification


44
At the outset, we note that the '786 patent is entitled "Variable Rate and  Variable Mode Transmission System." Consistent with the title of the  patent, the patentees, throughout the specification, use the terms "rate"  and "mode" to refer to separate and distinct concepts. In the summary of  the invention, the specification states that it is an object of the  invention to operate in:


45
a plurality of different modes and at any one of a plurality of different bit rates . . . . Still another object of the invention is to simply and easily vary the bit rates of the upstream and downstream channels, or the modes of the transceivers . . . . Another object is to either automatically control bit rate or mode by the CO or selectively control bit rate or mode by the subscriber.


46
'786 patent, col. 2, ll. 49-64 (emphasis added). Later, the Summary of the  Invention notes that the present invention "has the advantages of  conventional ADSLs, while allowing the data rate of the reverse control  signaling channel to be controllably increased so as to have a higher rate  transmission than ADSL in a bi-directional mode." Id. at col. 3, ll. 15-19  (emphasis added). The specification continues:


47
This variable rate / variable mode ADSL service will accommodate access to a wide variety of information providers . . . . In addition to variable bit rates for the control channel, the invention enables at least two modes for the ADSL transceivers, one providing bi- directional communications and the other providing asymmetrical communications.


48
Id. at col. 3, ll. 36-46 (emphasis added). Thus, before we even reach the  Detailed Description of the Preferred Embodiments, it is clear that the  '786 patent specification (in the Summary of the Invention) refers to the  terms "rate" and "mode" as two separate and distinct concepts. The term  "rate" describes the data rate within a given channel, while the term  "mode" differentiates between asymmetrical and bi-directional  communications.


49
The written description of the preferred embodiments also guides our  interpretation of the claim language, as claims must be read in light of  the specification. Scimed, 242 F.3d at 1340-41, 58 USPQ2d at 1062. We are  mindful of the fact that limitations from the specification may not be read  into the claims.  Comark, 156 F.3d at 1186, 48 USPQ2d at 1005. Indeed, Bell  Atlantic argues that by limiting the construction of the term "mode" to the  three broad categories described in the specification, the district court  improperly imported the limitations of one embodiment into the claim term.  We disagree.


50
We recognize that there is sometimes "a fine line between reading a claim  in light of the specification, and reading a limitation into the claim from  the specification." Comark, 156 F.3d at 1186, 48 USPQ2d at 1005. For  example, relying on Johnson Worldwide, Bell Atlantic argues that it is  impermissible to rely on the written description of a preferred embodiment  to limit the claim language. In Johnson Worldwide, we held that the meaning  of a claim term was not limited by its specific usage in the written  description of a preferred embodiment. 175 F.3d at 991, 50 USPQ2d at 1611.  We reasoned that the "[v]aried use of a disputed term in the written  description demonstrates the breadth of the term rather than providing a  limited definition." Id.; see also Pitney Bowes, Inc. v. Hewlett-Packard  Co., 182 F.3d 1298, 1310, 51 USPQ2d 1161, 1170 (Fed. Cir. 1999) (holding  that the written description of the preferred embodiments can set forth  more than one definition of a claim term).


51
However, Bell Atlantic's reading of Johnson Worldwide and characterization  of the role of the written description is too narrow. We held in Scimed,  242 F.3d at 1344, 58 USPQ2d at 1065, that the written description "can  provide guidance as to the meaning of the claims, thereby dictating the  manner in which the claims are to be construed, even if the guidance is not  provided in explicit definitional format."  Id. (emphasis added). Thus,  when a patentee uses a claim term throughout the entire patent  specification, in a manner consistent with only a single meaning, he has  defined that term "by implication." Vitronics, 90 F.3d at 1582, 39 USPQ2d  at 1577; see also Hockerson, 222 F.3d at 955, 55 USPQ2d at 1490.


52
In this case, in addition to the Summary of the Invention, the Detailed  Description of the Preferred Embodiments continues to use the terms "mode"  and "rate" to refer to two separate and distinct concepts. The  specification notes that the arrows used in figure seven "illustrate the  reversible mode feature of the system and no fixed data rate is given due  to the capability of the system to transmit at any one of a number of  different transmission rates." '786 patent, col. 10, ll. 64-67 (emphasis  added). This passage uses the term "rate" to refer to the speed of data  transmission, and uses the term "mode" to refer to the reversible mode  feature. When describing the microprocessor that controls the transceivers,  the specification states that "the variable transmission rates are  controlled by a first [program] and the mode of the transceiver is  controlled by a second [program]." '786 patent, col. 11, ll. 35-39  (emphasis added). Thus, the "mode" and "rate" of the transceiver are  controlled by separate programs.


53
Further, the specification states that the system "operates in one of three  selectable modes." '786 patent, col. 12, ll. 3-4 (emphasis added). The  specification describes the modes:


54
The first mode is conventional ADSL, which is appropriate for applications in which a subscriber wishes to view video data (using the fixed rate interface) or download a large amount of information in a predetermined downstream direction (utilizing the ethernet interface). The second mode is a bi-directional transmission mode which improves upon conventional ADSL by increasing the transmission rate of the upstream channel while decreasing the transmission rate of the downstream channel. This mode is preferable for certain interactive real-time applications such as video games and distance learning, in which a 8 Kbps or 16 Kbps upstream channel is insufficient for the flow of data in the upstream direction. An example of the channelization in the bi-directional mode in which the downstream and upstream channels are roughly equivalent is illustrated in FIG. 10 by channels 302', 304' and 306'.


55
The third mode is a reversible mode in which the asymmetrical transmission of data and other information is carried out in the same manner as conventional ADSL shown in FIG. 4, but the direction of flow is selectively reversed so that the upstream direction becomes the downstream direction and vice versa. This mode is especially useful for applications in which there are non-simultaneous, non-real-time, exchanges of large amounts of information in both directions.


56
'786 patent, col. 12, ll. 3-29 (emphasis added).


57
These passages refer to Figure 10 of the '786 patent, which illustrates the  described distribution of channel bandwidth. Channel 306' is the downstream  channel, while channel 304' is the upstream channel:


58
[Tabular or Graphical Material Omitted]


59
Although these passages offer the clearest description of the meaning of  the term "mode" in the specification, the remainder of the written  description also refers to the terms "mode" and "rate" as separate and  distinct concepts:


60
The structure of the chips . . . does not need to be changed to vary the mode of the transceiver or the transmission rates . . . [The] microprocessor/controller enables the rate or mode of the ADSL/AVR to be selected in any one of a number of ways . . . . A menu [may query for] the desired mode and/or data rate . . . . The changes in mode and rate for the channel can be accomplished by the ADSL/AVR interface . . . . Once the mode and rate has been set . . . . The ADSL/AVR thus effectively functions as a variable rate/variable mode modem.


61
Another passage refers to an "asymmetrical mode." '786 patent, col. 13, ll.  6-7 (emphasis added). Other passages discuss the "reversible ADSL mode."  '786 patent, col. 13, ll. 51-52. Still others explain how the system may  change from "bi-directional mode to ADSL mode." '786 patent, col. 14, ll.  7-8, 44-58.


62
In short, there is no question that the '786 patent specification uses the  terms "mode" and "rate" to refer to two different and distinct concepts.  The "rate" of data flow is characterized as the transmission rate within a  given channel. The "mode" is characterized by whether the relative  bandwidth between the upstream and downstream channels is symmetrical or  asymmetrical. Moreover, because the two terms are used separately and  distinctly, different "modes" cannot be created by varying the data rate  within one of the three broad categories. In other words, although a bi-  directional service "offering 192 Kbps in each direction is quite different  from one offering 1.1 Mbps," nevertheless, the two services do not  constitute different "modes." Thus, given the single meaning of the term  "mode" contemplated by the '786 patent specification, there are only three  possible permutations by which the relative bandwidth may be  characterized:  (1) where the first channel is smaller than the second  (conventional mode); (2) where the two channels are of roughly equal size  (bi-directional mode); and (3) where the first channel is larger than the  second (reversible mode).


63
We acknowledge that it is generally impermissible to limit claim terms by a  preferred embodiment or inferences drawn from the description of a  preferred embodiment. Johnson Worldwide, 175 F.3d at 992, 50 USPQ2d at  1612. However, that is not the case here. We note that "[t]he usage  'preferred' does not of itself broaden the claims beyond their support in  the specification." Wang Labs., Inc. v. America Online, Inc., 197 F.3d  1377, 1383, 53 USPQ2d 1161, 1165 (Fed. Cir. 1999). Moreover, unlike Johnson  Worldwide, this case does not involve the "[v]aried use of a disputed  term." Id. at 991, 50 USPQ2d at 1611. Instead, the patentees defined the  term "mode" by implication, through the term's consistent use throughout  the '786 patent specification. Vitronics, 90 F.3d at 1582, 39 USPQ2d at  1577. Given this definition, the three modes described in the Detailed  Description of the Preferred Embodiments describe the three possible modes  of the invention, and the claims are not entitled to any broader scope.  Wang, 197 F.3d at 1383, 53 USPQ2d at 1165.


64
b.   Prosecution History


65
The prosecution history also supports limiting the transceiver to the three  possible modes. During the prosecution of the '786 patent, the examiner  rejected the relevant claims as obvious over U.S. Patent No. 5,408,260  ("Arnon"). Arnon describes an ADSL transmission system and transceiver that  combines ADSL data with television signals, and transmits the data at  varying frequencies over coaxial cable wires. Arnon, col. 2, ll. 9-50.  Arnon describes a system that combines the ADSL data signals with the cable  television signal at ADSL "terminal units" within a residential building.  Arnon, col. 3, ll. 23-57. The examiner initially rejected the relevant  claims of the '786 patent because:


66
Arnon did not expressly detail that the controller selected the mode of operation for the transceivers. Arnon however taught that the receivers and transmitters could be automatically retuned to a different frequency when a terminal unit was faulty . . . . Therefore, it would have been obvious to one of ordinary skill in the [data processing] art at the time of the claimed invention that the Arnon system comprised control means which retuned the receivers and transmitters when a terminal unit was faulty so that it could communicate via another terminal unit. Also clearly it would have been obvious that this operation would have comprised selecting the new mode of operation for transmission of data. Further since the Arnon system operated on different channels at different rates it would have been obvious to a routineer that even in normal operation the Arnon system would have used a control means to change modes of transfer and speeds of transfer.


67
(emphasis added). Although the statements of an examiner will not  necessarily limit a claim, we observe that the examiner understood that the  "mode of transfer" was a separate and distinct concept than the "speed of  transfer."


68
Moreover, in an attempt to distinguish his invention from Arnon, the  patentees responded with various statements. Importantly, the patentee  argued:


69
In the present invention, the transmission bandwidth of channels 302, 304, and 306 are controlled for various modes using a microprocessor/controller in the ADSL/AVR unit.


70
(Emphasis added.) It is clear from this statement that the "mode" of the  present invention varies solely by changing the amount of bandwidth  allocated between the upstream and downstream channels. In subsequent  statements, the patentees described the "exemplary ADSL/AVR embodiment"  that operates "in one of three" modes:  conventional, bi-directional, and  reversible. The patentees observed that the invention allows one to perform  various functions "in the optimum mode and at the optimum transmission rate  for that function." (emphasis added). The patentees further distinguished  Arnon because:


71
[T]he ADSL unit of Arnon's subscriber loops appear to be conventional ADSL unit having a bandwidth distribution of the type illustrated in Applicants' Fig. 4. . . . Arnon's ADSL terminal comprises transmitters and receivers for communicating bi-directional data and control signals via the coaxial cable between the ADSL units and the subscriber, in each case modulated at a frequency which is not used for television signals. This is completely different from the present invention in which the ADSL terminal selectively changes the bandwidth for both control and data channels in the subscriber loop."


72
(emphasis in original). Bell Atlantic now contends that this statement  merely distinguishes the fact that Arnon's terminal units operated within a  residential unit, while the transceivers described by the '786 patent  operate outside the building, or "in the subscriber loop." It is true that  the emphasized language supports this distinction. However, the statement  also states that, "the present invention . . . selectively changes the  bandwidth." Thus, not only did the patentees distinguish that the invention  operated in the subscriber loop, but they also emphasized that a  conventional bandwidth distribution is "completely different" from the  invention's system of "selectively chang[ing] the bandwidth."


73
That the transceivers must operate in one of the three described modes is  further supported by the language of dependent claims 9 through 12:


74
9.The transmission system of claim 1, wherein said plurality of different modes includes a conventional ADSL mode and a bi-directional mode.


75
10.The transmission system of claim 1, wherein said plurality of different modes includes a conventional ADSL mode and a reversible mode.


76
11.The transmission system of claim 1, wherein said plurality of different modes includes a bi-directional mode and a reversible mode.


77
12.The transmission system of claim 1, wherein said plurality of different modes includes a conventional ADSL mode, a bi-directional mode, and a reversible mode.


78
'786 patent, col. 17, l. 59 to col. 18, l. 3. These four dependent claims  contemplate the only four possible permutations of a "plurality of  different modes." It is true that limitations stated in dependent claims  are normally not to be read into the independent claim from which they  depend. Karlin Tech., Inc. v. Surgical Dynamics, Inc., 177 F.3d 968, 972,  50 USPQ2d 1465, 1468 (Fed. Cir. 1999). However, our acknowledgment of  dependent claims 9-12 simply further demonstrates that the '786 patent  defined the term "mode" by implication to mean the relative allocation of  bandwidth between the first and second channel. Such a meaning leaves only  three possible modes: conventional, bi-directional, and reversible.


79
Bell Atlantic observes that independent claim 21 does not contain the  "plurality of different modes" language contained in claim 1.  Nevertheless, the district court held that the "ADSL/AVR transceiver"  described in claim 21 must also operate by dividing available bandwidth  between the two channels in conventional, bi-directional, and reversible  modes. We agree with the district court. The second sentence of the '786  patent abstract refers to ADSL transceivers "operating at variable rates  and in variable modes (ADSL/AVR)." (emphasis added). In the Summary of the  Invention, the '786 patent specification defines the invention as "an ADSL  having adjustable variable rate functionality (ADSL/AVR)." '786 patent,  col. 3, l. 10-11. The '786 patent uses the terms "transceiver," "ADSL/AVR,"  and "ADSL/AVR transceiver" interchangeably throughout the written  description and the prosecution history. Therefore, one of ordinary skill  in the art would understand that the transceiver described in claim 1 is  the same transceiver described in claim 21. Thus, at the same time the  patentees defined the term "mode" by implication, they also defined the  ADSL/AVR transceivers as those that operate in conventional, bi-  directional, and reversible modes by allocating bandwidth between the first  and second channels. For these reasons, the transceivers described in  claims 1 and 21 are construed synonymously with the definition of "mode"  set forth above.


80
2.   The First and Second "Channel" Limitation


81
Bell Atlantic also challenges the district court's claim construction of  the term "channel" as used in claims 1 and 21. The district court  determined that the first and second channels are "an amount of bandwidth  isolated for communications that may be either unidirectional or bi-  directional." Bell Atlantic argued that channel means "a one-way path  between communicating entities." Thus, we must determine whether the '786  patent specification requires the first and second channels to:  (1) be an  amount of bandwidth separated in frequency, and/or (2) support both  unidirectional and bi-directional communications.


82
a.   Unidirectional Channels


83
The district court determined that the first and second channels described  in claims 1 and 21 may support either unidirectional or bi-directional  communications. The district court noted that various phrases in the  specification described "two-way" channels, and reasoned that "the  inventors clearly intended 'channel' to encompass both one-way and two-way  segments of bandwidth." However, Bell Atlantic contends that the first and  second channels are instead "one way path[s]." We agree with Bell Atlantic  on this aspect of the interpretation of the "channel" limitation.


84
First, the language of the claims supports Bell Atlantic's contention that  the first and second "channels" are intended to encompass only one-way  communication. Claims 1 and 21 both describe a first transceiver  "transmitting or receiving signals, at a first transmission rate, on a  first channel, and transmitting or receiving signals, at a second  transmission rate, on a second channel." '786 patent, col. 17, ll. 9-12  (emphasis added). The use of the word "or" demonstrates that each  transceiver either transmits or receives on a single channel, but not both  simultaneously. Thus, the language of the claims themselves supports a  construction of the first and second "channels" that excludes bi-  directional or two-way communications.


85
Second, the written description defines the first and second channels as  those that support one-way communication. Throughout the written  description, the specification discusses the data channels as either  "upstream" or "downstream" channels. '786 patent, col. 2, l. 60; col. 3, l.  57; col. 7, l. 48; col. 8, l. 57; col. 12, ll. 10-29. Indeed, the written  description notes that in conventional ADSL systems, "channels 304 and 306  are unidirectional." '786 patent, col. 9, l. 8 (emphasis added). Other  passages refer to the "unidirectional" nature of the downstream or upstream  channels. '786 patent, col. 9, l. 50. Thus, it is clear that the  specification defines by implication the first and second channels as  supporting only unidirectional communication.


86
Covad nevertheless contends that the specification and prosecution history  also use the term "channel" to refer to bi-directional communications.  Therefore, Covad reasons that the term as used in claims 1 and 21 must be  construed to encompass both unidirectional and bi-directional  communications. It is true that the specification refers to a "two-way" or  bi-directional channel in numerous instances. '786 patent, col. 2, ll. 29-  30; col. 8, ll. 24-26; col. 8, ll. 44-46; col. 13, l. 7. It is also true  that during prosecution history, the patentees stated that "channel 302  provides connectivity for conventional [bi-directional] telephone  services." However, in each of these instances, it is evident that the  statements regarding the bi-directional channels refer to only the prior  art control channel, the signaling channel, or the POTS channel.  Conversely, wherever the specification discusses the first and second  (upstream and downstream) data channels referenced in the claims at issue,  it is clear that the communication is unidirectional.


87
"In circumstances such as this, where the language of the written  description is sufficient to put a reader on notice of the different uses  of a term, and where those uses are further apparent from publicly-  available documents referenced in the patent files, it is appropriate to  depart from the normal rule of construing seemingly identical terms in the  same manner. This entirely accords with the public notice function of  claims." Pitney Bowes, 182 F.3d at 1311, 51 USPQ2d at 1170. Thus, although  the term "channel" may encompass both unidirectional and bi-directional  communications, it is clear that the first and second data channel  limitations in claims 1 and 21 support only unidirectional communications.


88
b.   Frequency Separated Channels


89
The district court also held that the first and second "channels" are "an  amount of bandwidth" or "bands of frequencies" or "frequency channels." In  other words, the district court determined that the channels must be  separated by frequency. Bell Atlantic contends that the ordinary meaning of  the term "channel" is not limited to communication paths separated by  frequency. Indeed, as understood by one of ordinary skill in the art, the  ordinary meaning of the term "channel" is quite broad. Within the realm of  DSL technology, technical treatises refer to channels separated by  frequency ("frequency division multiplexing"), channels subdivided by time  ("time division multiplexing"), channels separated by "echo cancellation"  techniques, and channels subdivided by various "modulation" techniques.  See, e.g., E. Bryan Carne, Telecommunications Primer 223 (Prentice Hall 2d  ed. 1999); Michael Busby, Demystifying ATM/ADSL 37, 53-54, 205-206  (Wordware 1998).


90
However, the '786 patent specification defines the first and second  channels, by implication, as amounts of bandwidth, and thus, communication  paths separated by frequency. The summary of the invention references the  upstream and downstream channels. '786 patent, col. 2, l. 59; col. 3, l.  57. The written description of the preferred embodiments notes that the  upstream and downstream channels are illustrated in Figure 10 as channels  304' and 306'. '786 patent, col. 12, ll. 10-21. Figure 10, discussed above,  illustrates the upstream and downstream channels as channels separated by  frequency.


91
Moreover, the specification states that "the ADSL/AVRs used in the present  invention are a modification of, and an improvement over, conventional  ADSL." '786 patent, col. 8, ll. 15-17 (emphasis added). The specification  notes that conventional transceivers use "frequency multiplexing to divide  the available loop bandwidth into three channels 302, 304 and 306." '786  patent, col. 8, ll. 20-22. In numerous other passages, the specification  describes the channels in conventional ADSL systems as separated by  frequency. '786 patent, col. 8, l. 20; col. 8, l. 44; col. 8, l. 60; col.  9, l. 43; col. 10, l. 46. The specification notes that the ADSL/AVR system  of the present invention is similar to conventional ADSL systems. '786  patent, col. 10, ll. 60-61. Furthermore, the written description states  that the channelization between the upstream and downstream channels is  illustrated in Figure 10. '786 patent, col. 12, ll. 19-21. Both Figure 4  (conventional ADSL channelization) and Figure 10 (bi-directional mode  channelization) show that data channels 304, 306, 304', and 306' correspond  to bandwidths separated by frequency.


92
Moreover, the patentees stated during prosecution that "[i]n the present  invention, the transmission bandwidth of channels 302, 304, and 306 are  controlled for various modes." (emphasis added). This statement further  demonstrates that the channels used in the present invention are defined by  an amount of bandwidth. Thus, the only type of channels contemplated by the  '786 patent are those that occupy an amount of bandwidth- those that are  separated in frequency. Nowhere does the specification discuss channels  created by time-division multiplexing or echo cancellation. Indeed, in the  one reference to time division multiplexing, the specification states:


93
A down-stream control signal to the subscriber (not shown in Fig. 4) is time division multiplexed with the 1.544 mbps video signal on the 100-500 Hz carrier. This down-stream control signal, together with the digitized information and overhead, occupies a bit rate band of about 1.6 mbps.


94
'786 patent, col. 8, l. 66 to col. 9, l. 4 (emphasis added). The  specification refrains from identifying the time-division multiplexed  signal as a "channel," instead referring to it as a "signal."


95
Our construction does not limit the term "channel" through inferences drawn  from the description of a preferred embodiment. Johnson Worldwide, 175 F.3d  at 992, 50 USPQ2d at 1612. Neither does this case involve the "[v]aried use  of a disputed term." Id. at 991, 50 USPQ2d at 1611. Instead, the written  description "provide[s] guidance as to the meaning of the claims, thereby  dictating the manner in which the claims are to be construed, even if the  guidance is not provided in explicit definitional format."  Scimed, 242  F.3d at 1344, 58 USPQ2d at 1065. Because the patentees used the term  "channel" throughout the entire patent specification, consistent with a  single meaning, they defined that term "by implication." Vitronics, 90 F.3d  at 1582, 39 USPQ2d at 1577; see also Hockerson, 222 F.3d at 955, 55 USPQ2d  at 1490. Thus, in addition to being unidirectional, the first and second  channels described in claims 1 and 21 also constitute an amount of  bandwidth, and as such, are channels that are separated by frequency.


96
3.   "Selectively Changing"


97
Covad challenges the district court's construction of the "selectively  changing" limitation found in both claims 1 and 21. The district court  determined that "selectively changing" the first and second transmission  rates means that "a change is chosen and occurs, although it need not occur  during a


98
communication session." However, Covad posits that this limitation  requires a change "during a communication session."


99
As an initial matter, Bell Atlantic argues that we lack jurisdiction to  decide this issue because Covad did not file a cross-appeal, and Covad's  proposed claim construction would require modification of the judgment on  appeal. However, the general rule is that "without taking a cross-appeal,  the prevailing party may present any argument that supports the judgment in  its favor" as long as the acceptance of the argument would not lead to "a  reversal or modification of the judgment rather than an affirmance."  Carnival Cruise Lines, Inc. v. United States, 200 F.3d 1361, 1365 (Fed.  Cir. 2000). Thus, where the prevailing party in a motion for summary  judgment of noninfringement seeks "a claim construction more favorable to  [its] case than the construction adopted by the district court on summary  judgment, that would have no different result than affirmance of the  [judgment]." Genentech, Inc. v. Wellcome Found. Ltd., 29 F.3d 1555, 1562,  31 USPQ2d 1161, 1165 (Fed. Cir. 1994). Because Covad's proposed  construction of the "selectively changing" limitation would merely lead to  an affirmance of the judgment below, there is no requirement for a cross-  appeal on this issue.


100
It is true that the '786 patent specification explains that the  transmission rate or mode of the ADSL/AVR may be selectively changed  "during a communication session." '786 patent, col. 13, l. 65; col. 15, ll.  4-6. Indeed, the written description describes how a user may selectively  change the "mode and/or data rate." '786 patent, col. 14, ll. 11-16. At the  same time, however, the specification discusses selectively changing the  mode and rate at times other than during a communication session:


101
In addition to the direct subscriber selection or control of modes during a communication session mentioned above, the selection of modes may also be made indirectly, programmed or otherwise controlled so that it is executed upon the performance of some event.


102
'786 patent, col. 14, ll. 38-42. Elsewhere, the written description notes  that "[w]hen a request for a change in modes (e.g. from ADSL to bi-  directional) is received during or prior to a communication session, a  negotiation is made." '786 patent, col. 14, ll. 7-9 (emphasis added). The  specification also recognizes that "the subscriber could . . . change the  mode and download the file or information upon the occurrence of some  detectable event or at a designated time." '786 patent, col. 14, ll. 59-62  (emphasis added). Thus, the patent clearly contemplates the possibility of  selectively changing the transmission mode or rate at times other than  during a communication session. Consequently, the specification does not  define the limitation, either expressly or by implication, as a change made  only during a communication session. The varied use of this limitation  throughout the '786 patent specification "demonstrates the breadth of the  term rather than providing a limited definition." Johnson Worldwide, 175  F.3d at 991, 50 USPQ2d at 1611. Covad's proposed construction would  improperly import a limitation from the specification into the claim.  Comark, 156 F.3d at 1186, 48 USPQ2d at 1005.


103
Instead, the significance of the "selectively changing" and "selectively  operating" limitations is that the transmission mode or rate may be changed  either automatically or manually without altering the transceiver hardware.  The specification notes that a subscriber may "upgrade the capability of  the service to higher data rates in the future using a network management  system without altering the hardware." '786 patent, col. 11, ll. 57-59  (emphasis added). The specification also states:


104
[t]he structure of the chips in the chip set does not need to be changed to vary the mode of the transceiver or the transmission rates . . . . The use of a single chip set, capable of either transmitting or receiving conventional ADSL, at both ends of the transmission loop in the ADSL/AVR system . . . make it possible to easily and selectively implement the reversible ADSL mode.


105
'786 patent, col. 13, ll. 46-60. Moreover, in the prosecution history, the  patentees distinguished the fixed-bandwidth nature of Arnon:


106
[E]ven though Arnon teaches a fault induced substitution mode . . . the bandwidth or transmission rates in the ADSL loops during the fault mode or during the normal modes remain unchanged. Hence, it is submitted that Arnon fails to show, teach, or suggest selectively changing the first and second transmission rates in the subscriber loop.


107
(Emphasis added.)


108
Thus, the "selectively changing" and "selectively operating" limitations in  claims 1 and 21 mean that a change is chosen or occurs without alteration  of the transceiver hardware, although the change need not occur during a  communication session.

B. Infringement Analysis

109
Bell Atlantic does not argue, under our claim construction, that Covad's  accused DSL systems literally infringe the '786 patent. However, Bell  Atlantic contends that Covad's accused SDSL systems, which use echo  cancellation, could infringe under the doctrine of equivalents. Bell  Atlantic notes that it furnished evidence establishing that the single bi-  directional channel used by Covad's SDSL line cards is insubstantially  different from the two unidirectional channels described in claims 1 and 21  of the '786 patent. The district court rejected this argument, holding that  "Covad's SDSL transceivers perform substantially different functions in a  substantially different way to achieve substantially different results."


110
Bell Atlantic submitted the affidavit of Dr. Charles L. Jackson as expert  testimony supporting its position. Dr. Jackson states:


111
One could substitute the upstream SDSL communications path [in Covad's system] for one of the channels in claim 1 and the downstream SDSL communications path for the other channel in claim 1. The overlapping paths of the SDSL connection would perform the same function as the nonoverlapping channels required by Covad's view of claim 1. They are used in the same fashion as are the channels in the claim and they result in moving information signals to and from the customer premises as would the channels in Covad's interpretation of claim 1.


112
Bell Atlantic asserts that its expert testimony creates at least a genuine  issue of material fact to prevent summary judgment.


113
However, under the "all elements rule," there can be no infringement under  the doctrine of equivalents if even one element of a claim or its  equivalent is not present in the accused device. Pennwalt Corp. v. Durand-Wayland, Inc., 833 F.2d 931, 935-36, 4 USPQ2d 1737, 1739-40 (Fed. Cir.  1987) (en banc), cited in Festo, 234 F.3d at 587, 56 USPQ2d at 1887. Such a  determination must be premised upon a proper claim construction.  Insituform, 99 F.3d at 1109, 40 USPQ2d at 1610. Thus, if a court determines  that a finding of infringement under the doctrine of equivalents "would  entirely vitiate a particular claim element," then the court should rule  that there is no infringement under the doctrine of equivalents. Festo, 234  F.3d at 587, 56 USPQ2d at 1887 (citing Warner-Jenkinson Co., Inc. v. Hilton  Davis Chemical Co., 520 U.S. 17, 39 n.8, 41 USPQ2d 1865, 1875 n.8 (1997)).


114
In this case, Bell Atlantic's theory of infringement under the doctrine of  equivalents would entirely vitiate at least two limitations contained in  claims 1 and 21. The bandwidth of Covad's SDSL line cards is fixed with  physical filters, and the amount of bandwidth cannot be changed once the  transceivers are implemented and manufactured. Thus, Bell Atlantic's theory  of equivalence would entirely vitiate the claim limitations that require  the transceivers to "selectively change" or "selectively operate" the rate  or mode without changing the transceiver hardware. Moreover, Covad's SDSL  line cards use "echo cancellation" techniques to allow two-way communication  in a single frequency range over a single channel. Again, Bell Atlantic's  theory of equivalence would entirely vitiate the limitations that require  two unidirectional channels, separated by frequency. Accordingly, there can  be no infringement under the doctrine of equivalents.

IV. CONCLUSION

115
For the reasons discussed, the district court's grant of summary judgment  of noninfringement in favor of Covad is


116
AFFIRMED.

COSTS

117
Plaintiff-Appellant shall bear the costs of this appeal.



Notes:


1
 Bell Atlantic is now called Verizon Services Corporation,   a wholly owned subsidiary of Verizon Communications, Inc.,  formerly Bell Atlantic Corporation. For purposes of consistency, we refer to the plaintiff as Bell Atlantic.


2
 Echo  cancellation  allows  a  single  frequency range to   carry  both  the upstream and downstream signals.  The signals overlap and are separated by the well-known technique of local echo cancellation.


