Opinion ID: 785085
Heading Depth: 2
Heading Rank: 2

Heading: Multiplexing

Text: 44 Multi-Tech next challenges the district court's construction of the claim term multiplexing in claim 1 of the '649 patent and claim 11 of the '532 patent. Multi-Tech argues that the court improperly imported limitations from the specification into the claims by requiring that voice data have priority over computer data and that computer data be substituted for detected and discarded silence packets. 45 Microsoft responds by pointing out that the parties agreed that Multi-Tech acted as its own lexicographer in defining the term multiplexing. Therefore, Microsoft argues, the specification's definition of the term multiplexing to include the prioritization of voice packets, the detection and discarding of silence packets, and the transmission of computer data during periods of silence is the proper one. 46 We again begin our analysis with the claim language. Claim 1 of the '649 patent simply requires multiplexing outgoing voice and computer data packets and demultiplexing incoming voice and computer data packets. '649 patent, col. 47, ll. 14-25. Claim 11 of the '532 patent similarly requires multiplexing and demultiplexing voice and video data packets. '532 patent, col. 49, ll. 4-13. At the very least then, the plain language of the claims defines the term multiplexing as the combining of voice and computer data packets. The parties also agree that Multi-Tech acted as its own lexicographer in defining the term multiplexing to mean dynamic multiplexing, or the combining of voice and computer data packets for transmission through the same channel by dynamically changing the time allocations for transmission of each type of data. That interpretation is supported by the specification. See, e.g., '289 patent, col. 3, l. 2; id. at col. 7, ll. 39-42. 47 The parties disagree, however, as to the propriety of the district court's inclusion of two additional limitations in its interpretation of the term multiplexing. First, we agree with Microsoft that the court properly interpreted the term multiplexing to require the prioritization of voice data over computer data. In its discussion of multiplexing, the specification provides that voice data have higher priority than computer data to ensure the integrity of the real-time voice transmission. Id. at col. 35, ll. 57-58. Because maintaining the integrity of the voice data is central to the functioning of the claimed inventions, we read Multi-Tech as having defined the term multiplexing to require the prioritization of voice data over computer data. 48 However, we agree with Multi-Tech that the court improperly construed the term multiplexing to require the detection and discarding of silence packets and the transmission of computer data packets during periods of silence. The specification's references to those limitations are nothing more than disclosures of a preferred embodiment. Although those features may be desirable, nowhere does the specification indicate that they are necessary for the multiplexing function. Moreover, the method of detecting and discarding silence packets and transmitting only computer data packets during periods of silence is separately claimed in the dependent claims. '649 patent, col. 47, ll. 26-35; '532 patent, col. 49, ll. 14-23; see Comark Communications, 156 F.3d at 1187 (recognizing that the doctrine of claim differentiation, although not a hard and fast rule of claim construction, creates a presumption that each claim in a patent has a different scope). We therefore conclude that the term multiplexing does not include the limitations of detecting and discarding silence packets and transmitting computer data packets during periods of silence. 49