Invalidity dossier
US 5420854
Digital interface system
Current assignee: Hitachi Ltd
Added 9/23/2026, 5:48:23 PM
Active provider: DeepSeek · deepseek-flash
Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
Patent Overview — US 5,420,854
Title: Digital interface system
Patent number: US5420854A
Assignee: Hitachi Ltd (original and current assignee per the source)
Inventor: Masashi Hiraiwa
Priority date: 1990-06-18
Application: US08/153,107, filed 1993-11-17
Grant/publication date: 1995-05-30
Status listed: Expired – Fee Related; anticipated expiration 2012-05-30
Source: https://patents.google.com/patent/US5420854/en
Purpose. The patent addresses a multi-channel multiplexing switching system and inter-office signalling scheme in a digital switching network formed by connecting time-division switching systems over digital lines. It targets transmission efficiency when a circuit-switching system handling 64 kbps as a unit must carry calls of various bit rates — for example sub-rate calls of 8 k × n bps. The disclosed approach avoids permanently fixing transmission-line time slots per terminal bit-rate attribute, and provides a way to inform the opposite office of multi-channel call attribute information (the source notes that JP-A-1-120931 lacks such means).
Plain-language scope. Switching offices each contain a switch, digital trunk interface units, a sub-rate multiplexing and separating trunk, an outband call control signal unit (DCH) and a central control unit. The sub-rate trunk performs rate adaptation (e.g., CCITT V110 for data, compression for voice), multiplexes sub-rate channels and feeds an aggregate signal (1,536 kbps in the example) to the digital trunk interface; the receiving side separates the 8 kbps × n signal back to 64 kbps for the switch. Channel seizure is administered via a table recording used/unused 64 kbps B channels and their sub-channels. On a call request, the control unit searches for a B channel with a free sub-channel, checks the terminal's access rate, and either seizes or releases a sub-channel, or seizes a new unused B channel if the required rate is unavailable. A SETUP message carries a sub-channel identifier indicating position and number of sub-channels within the designated B channel, allowing the opposite office to seize the designated sub-rate channel or to select and signal a change.
What the excerpt does not establish. It does not provide claim text, the full specification, drawing contents (FIGS. 1–8 are referenced but not reproduced), detailed message formats or sequences beyond the described excerpt, prosecution history, or the scope of any specific claim. It does not describe later US5533022A, which merely shares a priority link in the source data.
Generated 10/1/2026, 9:43:17 PM
Cases on file (0)
Specific litigation cases in our database that name US patent 5420854. The free-form analysis below may also discuss cases beyond this list.
No cases on file mention this patent. Upload a CSV or add a case manually in Admin → Manage litigation cases.
Litigation summary
Past and pending lawsuits — plaintiffs, defendants, jurisdictions, outcomes, and notable rulings.
Proceedings on file (0)
All PTAB activity →AIA trial proceedings (IPR / PGR / CBM) filed at the USPTO Patent Trial and Appeal Board against this patent. Sourced from the USPTO Open Data Portal and refreshed every six hours; each proceeding number deep-links to the PTAB E2E docket.
No PTAB proceedings on file. This patent has not been challenged via IPR, PGR, or CBM. The absence is itself a signal — well-asserted patents eventually attract IPRs. The LLM analysis below may surface filings the ODP feed hasn’t indexed yet.
PTAB challenges
AIA trial proceedings at the USPTO Patent Trial and Appeal Board — IPR, PGR, and CBM. Petitioners, judge panels, claim-level invalidation outcomes from Final Written Decisions, and Federal Circuit appeals. The single most important defensive datapoint after litigation history.
Assignment history
Inventors, original assignee, and the chain of ownership recorded with the USPTO — including the correspondent attorney who recorded each assignment, since shell-LLC chains often share one repeat-player attorney even when the entity names look unrelated. Surfaces NPE / patent-troll patterns: shell-entity transfers, known asserters in the chain, repeat correspondent fingerprints, pre-litigation assignments, and bankruptcy fire-sales.
Prior art
Earlier patents, publications, and products that may anticipate or render the claims unpatentable.
Obviousness
Combinations of prior art that suggest the claimed invention would have been obvious under 35 U.S.C. § 103.
Extensions
Patent term adjustments, term extensions, continuations, divisionals, family members, and expiration dates.
Derivative works
Defensive disclosure: derivative variations of each claim designed to render future incremental improvements obvious or non-novel.