US 6820210

I'll search for authoritative information on this patent, including any 2026 CAFC docket activity.

Let me do a couple of targeted searches for any litigation or CAFC 2026 activity.

US Patent 6,820,210 — Analyst Summary

Search scope note: I searched for this exact number (6,820,210 / 6820210) on Google Patents, USPTO-facing mirrors (uspto.report), Justia, FreePatentsOnline, and general web/PTAB sources. I found no litigation, PTAB proceeding, or 2026 CAFC docket activity naming this patent. My CAFC-2026-specific searches returned either nothing or unrelated matters (e.g., Centripetal v. Cisco '856/'806 patents; Comtech/Oclaro IPRs). I did not find any authority indicating this patent is in front of the Federal Circuit in 2026. Treat "no 2026 CAFC activity found" as a negative search result, not a certified absence.

Bibliographic Data

Continuation chain (all now expired): US 6,269,452 B1 (Ser. 09/067,482, filed 1998-04-27) → US 6,430,700 B1 (Ser. 09/910,467, filed 2001-07-19) → US 6,615,362 B1 (Ser. 10/170,980, filed 2002-06-12) → US 6,820,210 B1 (Ser. 10/418,452, filed 2003-04-17).

Note on a literal-reading anomaly: the printed patent's Related Applications paragraph recites that the continuation "claims priority under 35 U.S.C. § 119" to Ser. No. 09/067,482. Read literally, that cites the foreign-priority statute, which is textually inconsistent with an ordinary §120 domestic continuation claim. I am reporting the identifier as printed rather than auto-correcting it; this may be a drafting/printing error in the patent.

Classifications: H04L45/28 (route fault recovery); H04L12/437 (ring fault isolation/reconfiguration); H04L45/22 (alternate routing). One third-party aggregator (Radaris) lists G06F 11/00.

Prior art cited on the face: ANSI T1.105.01-1995 ("American National Standard for Telecommunications—SONET—Automatic Protection Switching," Nov. 15, 1995) and Bellcore GR-1230-CORE ("SONET Bidirectional Line-Switched Ring Equipment Generic Criteria," Issue 3, Dec. 1996).

Abstract (as issued)

The patent provides a protection protocol for fault recovery (e.g., a ring wrap) for a two-line bi-directional ring network. A node identifies a problem with the connection to a first neighbor. The protocol simplifies coordination among nodes: nodes need not maintain a topology map of the ring identifying/locating each node. Independently operating rings can be merged, with the protocol automatically removing protection (e.g., a wrap) to form a single ring. Multiple protection-priority levels are provided so a high-priority failure (e.g., physical break) removes protection for a low-priority failure (e.g., signal degrade) on another link.

Plain-Language Overview of Each Independent Claim

There are 18 independent claims: 1, 2, 3, 24, 25, 26, 34, 37, 38, 39, 51, 52, 54, 55, 56, 60, 62, and 64. They are largely an apparatus set (1–34), a mirrored method set (37–53), a mirrored means-plus-function "system" set (54–61), and a mirrored computer-readable-medium set (62–65).

Priority/forwarding concept (claims 1, 2)

• Claim 1 — A node detects a problem on its link to a neighbor and sends a message about it to a second node; a fault-recovery procedure is started. If the second node already has a higher-priority situation, it ignores the message.
• Claim 2 — Same setup, but the inverse rule: if the incoming message describes a higher-priority situation than the receiving node's own, the receiving node forwards the message on to a third node.

APS messaging & timing concept (claims 3, 24, 25)

• Claim 3 — Nodes exchange Automatic Protection Switching (APS) packets with neighbors over the inner and outer rings; the transmission periods are user-configurable, and short and long periods are used to reduce APS traffic in steady state.
• Claim 24 — A receiving node checks whether a fault-recovery packet arrived on the long path. If not (i.e., short path), it is not forwarded. A long-path packet "may" be forwarded, but if it would have to traverse a wrapped connection, it is not forwarded.
• Claim 25 — Timing rule: a node sends a packet to a neighbor and checks whether there is an incomplete ring wrap. No wrap in progress → set the interval to an "idle time"; problem detected → set it to a shorter "protection time" used during protection; after the wrap completes, revert to idle time.

Wrap signaling concept (claims 26, 51)

• Claim 26 — A node detects a problem with a first neighbor, performs a wrap away from the failed side, sends a short-path message to that neighbor and a long-path message to its other neighbor. The first neighbor wraps on the failed side and returns an IDLE message with wrapped status on the short path. A long-path message that would have to cross a wrapped connection is not forwarded.
• Claim 51 — Method counterpart to claim 26.

Long-path packet handling / unwrap concept (claims 34, 52, 60, 64)

• Claim 34 — A node receiving a message: (a) if not sent on the long path → do not forward; (b) if long path, check whether the node itself originated it — if so, do not forward (loop suppression); (c) if not self-originated, compare priority against a "local situation" — if the message is lower priority, do not forward; if not lower, forward and decide whether to unwrap.

Method / system / medium counterparts

• Claim 37 — Method version of claim 1 (ignore message when receiver has higher-priority situation).
• Claim 38 — Method version of claim 2 (forward when message's situation outranks receiver's).
• Claim 39 — Method version of claim 3 (APS packets on inner/outer rings, user-configurable periods, short/long periods).
• Claim 52 — Method version of claim 34 (long-path determination, self-origination check, priority check, unwrap decision).
• Claim 54 — Means-plus-function (system) version of claim 1.
• Claim 55 — Means-plus-function version of claim 2.
• Claim 56 — Means for exchanging packets to identify a problem and for initiating fault recovery, with APS packets on inner/outer rings sent at user-configurable periods.
• Claim 60 — Means-plus-function version of claim 34.
• Claim 62 — Software in a computer-readable medium: exchange packets to identify a problem, initiate fault recovery, and maintain neighbor addresses gleaned from short-path messages.
• Claim 64 — Medium version of claim 34.

Representative dependents (context): claims 4–23 depend from claim 3 (claim 10 recites the LO/FS/SF/SD/MS/WTR/IDLE hierarchy; 11–13 the co-existence rules; 14–15 tie-breaking; 16–17 forwarding suppression; 18–19 wrap/long-path termination; 20–22 neighbor-address tracking and Wait-to-Restore; 23 pending-request handling). Claims 27–33 depend from 26 (Class I/II/III priority hierarchy, lockout, forced switch/signal fail, co-existence). Claims 35–36, 40–50, 53, 57–59, 61, 63, 65 are further dependents.

Key Technical Framework (from the specification)

• Built around Spatial Reuse Protocol (SRP) Automatic Protection Switching (APS).
• Priority hierarchy (highest → lowest): Lockout of Protection (LO) > Forced Switch (FS) > Signal Fail (SF) > Signal Degrade (SD) > Manual Switch (MS) > Wait-to-Restore (WTR) > No Request (IDLE).
• Class I = LO (highest); Class II = FS, SF; Class III = SD, MS, WTR, IDLE (lowest). Class I and II requests may co-exist; Class III requests may not co-exist (to avoid ring partitioning). Ties among equal Class III requests resolve to the first to complete long-path signaling, and inner/outer-ring ties resolve to a pre-determined ring (e.g., outer).
• The stated advantage over conventional SONET BLSR is elimination of the need to manually configure/maintain a per-node ring topology map, and automatic reconciliation when rings are merged or new nodes added.
• Explicit incorporation-by-reference language covering the earlier applications in the family.

Uncertainty / Caveats

1. No 2026 CAFC docket for this patent was located. Given the patent expired (anticipated) on April 27, 2018, contemporaneous 2026 Federal Circuit activity is unlikely; any 2026 docket involvement would more plausibly be appellate fallout from a PTAB or district-court matter, and I found none.
2. No PTAB proceeding (IPR/PGR/CBM) naming 6,820,210 was found in my searches.
3. The $138,076,000 "approximate value" shown on patentleaderboard.com is a third-party heuristic estimate, not an authoritative valuation or damages figure, and I would not rely on it.
4. Assignee naming appears as "Cisco Technology, Inc." (patent face) vs. "Cisco Technology Inc" (Google Patents); these refer to the same entity.
5. Inventor name spelling: the patent PDF OCR renders the first inventor as "Felsal" / "Feisal" Daruwalla; other sources show "Feisal." I read this as an OCR artifact rather than two different people, but flag it as a naming uncertainty.

Sources: https://patents.google.com/patent/US6820210/en ; https://patentimages.storage.googleapis.com/aa/14/57/d94f16e5ae37ec/US6820210.pdf ; https://patents.justia.com/patent/6820210 ; https://uspto.report/patent/grant/6820210

I'll search for litigation involving US patent 6820210 specifically. Let me run several targeted searches.

The initial searches didn't surface litigation. Let me dig into litigation-specific databases and patent number variations.

Litigation Search Results: US Patent 6,820,210

Bottom line: I could not identify any known litigation — district court, ITC, or Federal Circuit — involving U.S. Patent No. 6,820,210 specifically. The searches I ran (including targeted queries for "6820210 litigation," "6,820,210 lawsuit," case dockets, and the Unified Patents / RPX litigation portals) returned no case in which this patent number appears as an asserted patent. I want to be explicit that this is an absence of found results rather than a certified "never litigated," and I did not have direct access to run a live PACER docket-query or a Lex Machina/Docket Navigator patent-centric search, which are the authoritative tools for a negative-confirmation of this kind.

No cases found

There are no plaintiff(s), defendant(s), jurisdiction, case number, filing date, or outcome to report, because no case was located. Searches for the exact number "6820210" and the formatted "6,820,210" surfaced only: (a) the patent's own Google Patents/Patent Leaderboard pages, (b) unrelated cases involving different patent numbers, and (c) PTAB/IPR documents citing other patents. Nothing matched.

Patent identification (matches the authoritative full text you supplied)

• Patent No.: US 6,820,210 B1
• Title: "System and method for fault recovery for a two line bi-directional ring network"
• Assignee: Cisco Technology, Inc. (original assignee Cisco Technology, Inc.)
• Inventors: Feisal Daruwalla; Hon Wah Chin; David Tsiang; George Suwala; Tony Bates
• Priority date: 1998-04-27
• Filing date: 2003-04-17 (continuation of Ser. No. 10/170,980, now US 6,615,362; itself a continuation chain through US 6,430,700 and US 6,269,452)
• Grant date: 2004-11-16
• Status: Expired – Lifetime (anticipated expiration 2018-04-27)

Why the absence is plausible (context, not confirmation)

• Owner profile: The patent is held by Cisco Technology, Inc., an operating company. Cisco's networking patent portfolio is overwhelmingly defensive and is rarely asserted offensively in litigation; this asset appears consistent with that pattern.
• Patent family: The four-member family (US 6,269,452; US 6,430,700; US 6,615,362; US 6,820,210) is directed to Cisco's Spatial Reuse Protocol (SRP) / Automatic Protection Switching (APS) ring-recovery technology, an internal infrastructure technology rather than a consumer-facing product feature typically targeted by assertion campaigns.
• Expiration: With the patent expired as of 2018-04-27, any live infringement action would be time-barred for post-expiration conduct, and past damages windows have long closed — further reducing the likelihood of any active litigation.

Recommended verification steps before relying on this

If you need a defensible negative finding (e.g., for a freedom-to-operate or due-diligence memo), I recommend querying the primary litigation databases directly, since my web searches are not a substitute:

• PACER / CourtListener (RECAP) — full-text search for "6,820,210" and "6820210."
• Unified Patents Portal litigation case list (https://portal.unifiedpatents.com/litigation/caselist) — filter by patent number.
• Docket Navigator / Lex Machina / RPX Insight — patent-number and patent-family searches, which also catch cases where the number appears only in an exhibit or claim chart.
• PTAB — check for any IPR/PGR on the family members, which often correlates with parallel district-court campaigns.

Caveat per my operating rules: I interpret the number literally as 6,820,210. If your source intended a different number (e.g., 6,820,201 or 6,820,210 vs. a similarly numbered patent), the result could differ — but I did not auto-correct, and I found no litigation for the number exactly as given.

I'll verify the structured block's "no proceedings" finding against live sources before writing.

Let me run a few more targeted checks before concluding.

One more check on the sibling patents and any litigation that might have spawned PTAB activity.

Proceedings overview

Zero AIA trial proceedings are on file for US 6,820,210 — the USPTO ODP structured block returns none, and my independent checks of PTAB petition documents, IPR docket references, and litigation filings surfaced no IPR, PGR, or CBM naming the '210 (or any of its three continuation siblings) as the challenged patent. The defense posture this creates is unusual and, for a defendant, strongly favorable — but for reasons that have nothing to do with PTAB: the patent expired on 2018-04-27, so the absence of IPRs reflects a patent nobody needed to kill, not a patent that survived attack.

Proceedings on file

None. There is no proceeding to describe — no petitioner, no panel, no institution decision, no FWD, no settlement, no appeal, no estoppel.

I want to be explicit about the scope of that finding, because "no PTAB activity" is only useful if you know what it excludes:

• No IPR petition appears in PTAB petition records or docket references for U.S. Patent No. 6,820,210. Searches returning PTAB petition text in this space hit unrelated patents (e.g., IPR2020-01357 on the '485 Ethernet-ring patent; Cisco's ChriMar and Centripetal IPRs; the Corsica/Egenera and Dynamic Mesh matters). None involve the '210.
• No IPR appears to have been filed against the '210's continuation family either: US 6,269,452, US 6,430,700, and US 6,615,362. All four share the 1998-04-27 priority date and effectively identical specifications.
• No CBM is possible now, and none was filed. CBM review under AIA § 18 was tied to financial-product/service claims (poor fit for a ring-network protection protocol), and the program sunset on 2020-09-16.
• No PGR was ever available. The '210 has an effective filing date of 1998-04-27 (application 10/418,452, filed 2003-04-17, is the fourth in a continuation chain back to Ser. No. 09/067,482). PGR applies only to patents with an effective filing date on or after 2013-03-16.

I could not find the '210 itself asserted in any district court litigation. For context, Cisco was the defendant in the notable ring-network patent war — Telcordia Technologies, Inc. v. Cisco Systems, Inc., D. Del. — but that case involved Telcordia's patents (U.S. 4,835,763; Re. 36,633; 6,456,590 '306), including claim construction over "ring" and "multiplexed subrate communications." That is a different patent family and a different posture: Cisco was the accused infringer, and the '210 was Cisco's own asset. See Telcordia Tech., Inc. v. Cisco Sys., Inc., 612 F.3d 1365 (Fed. Cir. 2010).

Strategic summary

Claim status: every claim is UNTESTED — none canceled, none sustained, none adjudicated. All 65 claims remain as issued (independent claims 1, 2, 3, 24, 25, 26, 34, 37, 38, 39, 51, 52, 54, 55, 56, 60, 62, and 64, with the remainder dependent). There is no FWD, no certificate of cancellation, and no reexamination certificate narrowing any claim. That sounds like the patent is "untouched," and legally it is — but the practical consequence is not "the patent is hardened." It is that the patent's validity was never worth contesting because its enforceable life ended on 2018-04-27 (20 years from the 1998-04-27 priority filing; Google Patents lists the same anticipated expiration and a status of "Expired – Lifetime").

Estoppel landscape: there is none. Because no IPR was ever instituted and no FWD ever issued, 35 U.S.C. § 315(e)(2) estoppel never attached to anyone. No petitioner is barred from raising any ground — §§ 102, 103, or 112 — in district court or at the PTAB. Conversely, there is also no petitioner-side record of invalidity findings, no claim-construction order from the Board, and no IPR transcript to mine. A defendant today starts with a completely clean prior-art slate. The relevant prior art on the face of the '210 is standards-based and publicly citable: ANSI's SONET Automatic Protection Switching standard (1995), Bellcore GR-1230-CORE (Dec. 1996), and Bellcore GR-1230-ILR (Dec. 1996) — all of which predate the 1998 priority date by more than a year. The single most potent ground, though, is not art-based: it is the expiration date.

Pattern signals. There is no repeat-petitioner pattern because there are no petitions at all. There is no defensive aggregator (no Unified Patents, RPX, or similar) anywhere in the chain — and given that the '210 is a Cisco-originated asset and no assignment away from Cisco is shown in the record, that is unsurprising. Some third-party analytics sites assign the '210 an eye-catching estimated value (e.g., the Patent Leaderboard lists a ~$138M "approximate value" for the '210 and its Cisco SRP siblings). Treat that as a heuristic score derived from family/forward-citation data, not as evidence of licensing revenue, assertion history, or litigation exposure — I found no evidence of any of those. There is also no evidence of a Cisco appeal to the Federal Circuit on this patent, because no PTAB decision existed to appeal.

Recommended next steps

If you have received a demand or been sued on US 6,820,210, the expiration date — not the PTAB — is your dispositive defense. Three points to run down immediately:

1. Demand the damages period in writing. 35 U.S.C. § 286 caps recovery at six years before the filing of the complaint. A complaint filed today (2026-10-01) reaches back only to 2020-10-01 — which is entirely after the 2018-04-27 expiration. There is no recoverable infringement window. If the demand letter cites the '210, quote § 286 and the anticipated expiration date back at the sender.
2. Confirm the expiration date independently before you rely on it. Check the maintenance-fee history and any terminal disclaimer or patent term adjustment in the file wrapper at USPTO PatentCenter rather than trusting a single source. My basis is Google Patents' "Anticipated expiration 2018-04-27 / Expired – Lifetime," which is consistent with a 20-year term from the 1998-04-27 priority date, but you should verify against the official record. If the patent instead expired earlier for non-payment of maintenance fees, that only helps you.
3. Identify who is actually asserting it, and whether they own it. The '210 is recorded as Cisco Technology, Inc., assignee — a practicing entity that has historically been a defendant in this space, not an assertion plaintiff. If a non-Cisco entity is demanding payment on the '210, request the complete chain of title through USPTO Assignment records before responding. A demand on an expired, never-asserted patent by a party with a defective chain is itself worth documenting.

On the PTAB specifically: do not file. An IPR on the '210 would be an expensive way to obtain relief you already have by operation of law. For completeness, IPR petitions can be filed against expired patents, but there is no live controversy or recoverable damages here, and no petitioner-side benefit to offset the cost. Likewise, ex parte reexamination remains theoretically available to anyone post-expiration (no § 315(b) time bar), but it is unnecessary and would not change your exposure.

Link for verification: the patent's full text, claims, classification, and expiration data are at Google Patents – US6820210B1. PTAB proceeding queries can be run directly through the PTAB Case Tracking portal — I ran that query and it returns nothing for this patent number.

One honest caveat on the "absence is a signal" heuristic. Normally, a well-asserted patent attracts IPRs. Here, the absence of IPRs is not evidence of a robust patent. The '210 was in force throughout the entire IPR era (September 2012 through April 2018), so challengers had a five-and-a-half-year window — and nobody used it. The most likely explanation is that the '210 was Cisco's own defensive asset, was never deployed as an offensive weapon, and sat in an SRP patent family that the market regarded as standards-encumbered rather than litigation-worthy. Do not read the empty PTAB docket as "this patent is battle-tested." Read it as "this patent was never worth shooting at."

I'll research this patent's ownership record across the sources you named.

Let me dig into the specific assignment records and any litigation history.

Ownership Analysis — US Patent 6,820,210 B1

Patent: "System and method for fault recovery for a two line bi-directional ring network"
Grant: 2004-11-16 · App: 10/418,452 filed 2003-04-17 · Priority: 1998-04-27 · Status: Expired – Lifetime (anticipated expiration 2018-04-27)

Sourcing caveat up front: I was able to pull the authoritative patent text and the Google Patents legal-events data for this patent, but I was not able to render the live USPTO Assignment Center result set for patent 6,820,210 in this session (the search returned only generic assignment-office documents for unrelated patents). Accordingly, no reel/frame numbers below are invented or inferred — I report only what the retrieved records actually establish and flag the rest as unverified. Verify directly at assignment.uspto.gov (or assignmentcenter.uspto.gov) by searching patent number 6820210.

Inventors

Pattern note: No unusual inventor-departure pattern is evidenced. These are the R&D team behind Cisco's Dynamic Packet Transport (DPT) / Spatial Reuse Protocol (SRP) ring protection work ("Intelligent Protection Switching," IPS). There is no record of a spinoff, and the continuation chain (below) is an internal prosecution ladder, not a portfolio breakup. I found no evidence of the "all inventors depart within 12 months" fire-sale precursor.

Original assignee

Cisco Technology, Inc., 170 West Tasman Drive, San Jose, CA 95134 — the patent-captive licensing/holding subsidiary of Cisco Systems, Inc. Google Patents lists Cisco Technology, Inc. as both original and current assignee.

• Product embodying the claims: Yes, strongly. The claimed APS/IPS protection protocol maps to Cisco's DPT (Dynamic Packet Transport) product line (Cisco 10720, GSR/12000-series line cards, ONS 15104 regenerator) running SRP, documented in Cisco's own DPT white papers and standardized in the RPR/IEEE 802.17 discussions. The inventors' SRP work is the direct antecedent of that hardware.
• Primary line of business: Networking equipment / software.
• Current status: Operating. Cisco Systems, Inc. (NASDAQ: CSCO) is a going concern; Cisco Technology, Inc. remains an active patent-holding subsidiary. No bankruptcy, dissolution, or assignment-in-lieu evidenced.

Assignment timeline

No post-issuance recorded assignment is evidenced in the retrieved records. The Google Patents legal-events table for US 6,820,210 lists only prosecution/term events (priority, filing, grant, publication, anticipated expiration) and no assignment, security-agreement, merger, or change-of-name entries. There is no evidence anywhere in the retrieved record of the patent ever leaving Cisco's hands.

Because I could not load the Assignment Center result set directly, I am not asserting that the file is empty — I am stating that (a) no post-issuance transfer is evidenced by any source retrieved, and (b) I could not confirm the reel/frame of any inventor→Cisco Technology, Inc. record. Per your rule, I decline to supply reel/frame numbers I cannot verify. The practical read: ownership remains with Cisco Technology, Inc. / Cisco Systems, Inc.

For completeness, the four applications in this family — which are continuations of one another, not ownership transfers — are:

• 1998-04-27 filed — App 09/067,482 → issued as US 6,269,452 (root application; original Cisco disclosure)
• 2001-07-19 filed — App 09/910,467 → issued as US 6,430,700 (continuation)
• 2002-06-12 filed — App 10/170,980 → issued as US 6,615,362 (continuation)
• 2003-04-17 filed — App 10/418,452 → issued as US 6,820,210 (continuation; the patent at issue)

All four name the same Cisco assignee and the same inventor group. This is a prosecution-ladder pattern, not a cascading-transfer pattern — the distinction matters for the NPE screen below.

Timeline diagram

timeline
    title Ownership of US 6820210
    1998 : Parent app filed by Cisco inventors
    2001 : First continuation filed
    2002 : Second continuation filed
    2003 : Third continuation filed
    2004 : Patent US 6820210 issued
         : Assignee Cisco Technology Inc
    2018 : Patent term expired

(This diagram reflects the continuation ladder and record status, since no ownership-transfer events were evidenced.)

NPE / troll-pattern signals

1. Shell-entity transfer — not present. No assignment to any "IP / Holdings / Licensing / Ventures" LLC appears. Current assignee is the operating company's own subsidiary (Cisco Technology, Inc.), which per Google Patents is also the original assignee.

2. Known asserter in the chain — not present. Cisco appears on no relevant NPE/assertion list for this patent. I found no match to Acacia, Marathon, IV, Wi-LAN, Conversant, Pendrell, Round Rock, etc.

3. Repeat correspondent across the chain — not determinable. No assignment records (and hence no correspondents of record) were retrieved for this patent, so recurrence cannot be assessed. This is the one signal I genuinely cannot clear — it is untested, not negative.

4. Cascading transfers — not present. The four family entries are continuations sharing one owner and one inventor roster; there is no chain of LLCs and no sub-24-month ownership churn. Do not mistake the family listing for a transfer chain.

5. Pre-litigation transfer — not present. I found no infringement action naming US 6,820,210 as an asserted patent, and no assignment dated near any such suit. (Cases surfacing near Cisco ring technology — Corrigent v. Cisco/Arista (2022) and Monarch Networking Solutions v. Cisco (E.D. Tex., 2:20-cv-00015) — assert different patents and do not involve 6,820,210.)

6. Bankruptcy fire-sale — not present. Cisco has no relevant bankruptcy proceeding; no assignment-in-lieu of foreclosure evidenced.

7. Privateering — not present. No transfer to a third-party asserter acting on Cisco's behalf.

8. Defensive aggregator — not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. (It terminates at Cisco itself.)

Verdict

Insufficient data — but with the important substantive finding that every affirmative NPE indicator tested negative. The only supportable conclusion is that US 6,820,210 remained with its operating-company owner, Cisco Technology, Inc. (Cisco Systems), through expiry in 2018: a single-owner prosecution-ladder family (Apps 09/067,482 → 09/910,467 → 10/170,980 → 10/418,452) with no recorded post-issuance transfer, no LLC shell, no known asserter, no bankruptcy sale, and no defensive-aggregator acquisition.

I deliberately stop short of "Operating-company assertion," because that label requires the owner to be actively suing actual competitors on this patent, and I found no suit asserting 6,820,210 (Cisco's notable ring-adjacent litigation, e.g. the Arista ITC matter, rested on different patents such as 7,340,597). It also is not "Defensive / non-asserting" in the aggregator sense — Cisco is a commercial enforcer generally, not an anti-NPE neutralizer. Given the assignment record itself could not be rendered live, "Insufficient data" is the honest bucket.

To close the one open item (signal #3), pull the Assignment Center result for 6820210 and record any inventor→Cisco Technology, Inc. reel/frame plus its correspondent of record. If that record shows the standard Cisco in-house/outside filing correspondent and no later entry, the case is a clean operating-company ownership and the verdict can be upgraded accordingly.

Verify: USPTO Assignment Center · Assignment Search · Google Patents US6820210

I'll start by pulling the authoritative citation record for US 6,820,210 from USPTO/Google Patents, since the full text you supplied includes forward citations ("Cited By" and "Families Citing this family") but not the examiner-cited "References Cited" list.

I now have the examiner-cited "References Cited" list from the patent's front page (via Justia and the patent PDF). Let me verify the bibliographic details for each cited reference so I can give accurate citations and dates.

Prior-Art Analysis — US 6,820,210 B1

Analyst note on scope and method. I confirmed the target via USPTO/Google Patents/Justia as US 6,820,210 B1, "System and method for fault recovery for a two line bi-directional ring network," Cisco Technology, Inc., inventors Daruwalla, Chin, Tsiang, Suwala, Bates; priority 1998-04-27, filed (as a continuation) 2003-04-17, granted 2004-11-16, expired 2018-04-27. I then pulled the examiner-cited "(56) References Cited" list from the patent front page (Justia reproduction and the patent PDF at patentimages.storage.googleapis.com/aa/14/57/d94f16e5ae37ec/US6820210.pdf), which you supplied only in truncated form. My search-step budget was exhausted partway through verifying individual bibliographic records, so I flag confidence per reference rather than overstate.

Two structural caveats you must weigh before using this for any 102 opinion:

1. A front-page citation is not a §102 finding. These entries are an examiner/IDS citation list; the examiner included no "X" relevance coding (unlike a PCT search report). Several are clearly background art (network topology, bandwidth allocation), not anticipatory art. Mapping a reference to a claim requires the reference's full text and an element-by-element comparison, which the citation list alone does not provide.
2. Cutoff date. The effective filing/priority date is 1998-04-27. §102(a)/(b) art must publish before that date; §102(e) art must have a U.S. filing date before that date even if it granted later. All sixteen U.S. references below clear one of those thresholds, but the four that granted in 1999–2003 do so only via §102(e) and only if their underlying filing predates 1998-04-27.

A. Examiner-cited U.S. patent references

B. Same-family references on the front page — NOT prior art

These three were cited against the continuation but are the patent's own ancestors (same inventors, same Cisco assignee, same disclosure).

§102(e) "by another" trap for less-experienced reviewers: these share inventors and assignee with 6,820,210, so they fail the "by another" requirement and cannot anticipate. Do not treat them as art.

C. Non-patent literature (all §102(b))

These are the most likely primary references for the APS-mechanism and priority-hierarchy claims, because the patent itself frames the invention against SONET/Bellcore APS practice.

D. Bottom line and honesty flags

• Strongest anticipated-claims exposure: US RE37,401 E and US 5,737,310 (Goto) for the core independent claims 1, 2, 26, 37, 38, 51; the Bellcore GR-1230 documents and the ANSI APS standard for the hierarchy/preemption claims 9, 10, 27–33, 44, 45; US 5,319,633 (Geyer) for the neighbor-address claims 20, 48, 58.
• Weak/likely non-anticipatory: US 6,314,110 (Cisco sibling; different invention), US 5,949,755 and US 6,512,740 (post-priority grants reachable only under §102(e) and depending on filing date), and the three Daruwalla family members (not art at all).
• Verification gaps — stated plainly. I confirmed full titles/dates for US 5,319,633, US RE37,401, US 6,314,110, ANSI T1.105.01, and the Bellcore documents. For several older references (US 4,847,610; 5,341,364; 5,442,620; 5,469,428; 5,550,805; 5,663,950; 5,712,968; 5,737,310; 5,949,755; 6,512,740) I have confirmed the number, inventor, and grant date from the patent front page but did not independently re-verify the exact title/assignee, so I have marked those descriptions "title unverified." Do not quote those titles as fact without a full-text check on Google Patents/PatentCenter.
• Method caveat. This is a citation-and-mapping assessment, not a validity opinion. The §102 claim mappings above are preliminary hypotheses of where each reference's known disclosure could land; none should be represented as an established anticipation without reading each reference against each claim element. The claim numbers I cite correspond to the 65 issued claims reproduced in the full text you supplied.
• Consistency with the earlier section: this is consistent with the litigation summary — an expired Cisco defensive asset with a self-citation-heavy reference list and no assertion history. No contradiction found; the only correction is that the previously supplied full text omitted the §(56) reference list, which I recovered here.

I'll ground the prior-art references before analyzing. Let me run targeted searches on the key references on this page.

Obviousness Analysis — U.S. Patent No. 6,820,210 B1 under 35 U.S.C. § 103

Patent: US 6,820,210 B1 — "System and method for fault recovery for a two line bi-directional ring network"
Assignee: Cisco Technology, Inc.
Effective filing date (earliest priority): April 27, 1998 (Ser. No. 09/067,482)
Continuation filed: April 17, 2003 (Ser. No. 10/418,452)
Claims: 65 (18 independent: 1, 2, 3, 24, 25, 26, 34, 37, 38, 39, 51, 52, 54, 55, 56, 60, 62, 64)

0. Bottom line up front

The claims of the '210 patent are, in substance, a functional restatement of the SONET Bidirectional Line-Switched Ring (BLSR) Automatic Protection Switching (APS) protocol — the K1/K2 request-and-status signaling, the short-path/long-path propagation, the request priority hierarchy, the wrap-at-both-ends-of-the-failed-span behavior, the Wait-to-Restore state, and the squelching/co-existence rules — ported onto a packet ring environment. Both of the references cited on the face of the patent (ANSI T1.105.01-1995 and Bellcore GR-1230-CORE) teach those protection-switching principles in detail, and they are in the same field, addressing the same problem (ring fault recovery).

The strongest § 103 grounds are therefore:

1. GR-1230-CORE alone (single-reference obviousness) for the bulk of the independent claims and many dependents;
2. GR-1230-CORE in view of ANSI T1.105.01-1995 for the priority hierarchy, co-existence, tie-break, and state-transition limitations; and
3. GR-1230-CORE + T1.105.01 + U.S. 6,314,110 for the packet-ring framing limitations (APS packets carried over counter-rotating inner/outer rings, user-configurable transmission periods).

The weakest limitations are the timing-value specifics (claim 25's "idle time" vs. "protection time" and claim 22's WTR-reset-on-neighbor-change), which rest on predictable design-choice reasoning under KSR rather than literal disclosure.

Important timing caveat: almost all references in the "Cited By" table on the Google Patents page are later than the April 27, 1998 priority date and therefore do not qualify as § 102/§ 103 prior art. They are useful as evidence of the ordinary skill level and of the state of the field, not as anticipating art. I detail this in § 2.

1. Governing legal framework

• Pre-AIA § 103(a) applies. All claims have an effective filing date of April 27, 1998, well before the AIA's March 16, 2013 first-inventor-to-file cutoff; the 2003 continuation does not move the effective date for these claims (no claim has post-2013 support). Obviousness is judged as of the 1998 priority date.
• The Graham v. John Deere factors govern: (1) scope and content of the prior art; (2) level of ordinary skill; (3) differences between the claims and the prior art; (4) secondary considerations (objective evidence of non-obviousness).
• Under KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007), a combination is obvious where the elements are known, the combination is of a type described in the prior art, and there existed a design incentive, market pressure, or a predictable variation — a "motivation to combine" need not be explicit in a single reference and can arise from the nature of the problem to be solved. A predictable and finite set of identified solutions supports "obvious to try."
• Because the patent is a continuation in a family of four with essentially identical disclosures, the disclosure of the parent applications is not prior art to the '210 claims (same inventors, same assignee, overlapping disclosure — not "by another").

2. Scope and content of the prior art (the "Prior Art section")

2.1 References that actually qualify as prior art (pre-1998-04-27)

Documented disclosures of GR-1230 / T1.105.01, confirmed by search:

• GR-1230's table of contents confirms § 6.2.1 "Switch Initiation Criteria" (split into "Externally Initiated Protection Switching Commands (OS or WS)" and "Automatically Initiated Protection Switch Requests"), § 6.2.2 "Bit-Oriented Protocol for K1/K2 Bytes," § 6.2.2.1 "Steady State Behavior," § 6.2.2.2 "State Transition Rules," § 6.2.2.3 "Examples of Protection Switching in a BLSR." (Telcordia GR-1230 TOC — http://telecom-info.telcordia.com/ido/AUX/GR_1230_TOC.i04.pdf)
• The K1/K2 byte field semantics are well established: K1 bits 1–4 = switching request; K2 bits 1–4 = source node ID; K2 bit 5 = path code (short/long); K2 bits 6–8 = status. (Keysight GR-1230 ring-APS summary — https://www.keysight.com/tm/en/assets/9018-40820/user-manuals/9018-40820.pdf)
• The priority order used by SONET APS/BLSR is, highest→lowest: Lockout of Protection (LO) > Forced Switch (FS) > Signal Fail (SF) > Signal Degrade (SD) > Manual Switch (MS) > Wait-to-Restore (WTR) > No Request — exactly the ordering recited in claim 10. (Cisco APS documentation summarizing the "APS triggering hierarchy" — https://www.cisco.com/c/dam/global/de_at/assets/docs/mpls_juni03.pdf; Cisco POS/APS guide.)
• GR-1230 R6-72 establishes that the K1/K2 bytes are always destined to an adjacent node (short or long path), which is the mechanism by which a node learns its neighbor's identity — relevant to claims 20/48/58/62. (Confirmed in US 2002/0087733 A1, ¶ [0045]–[0046].)

2.2 References on the page that do not qualify as prior art

Every entry in the Google Patents "Cited By" table bears a priority date of 2000 or later (e.g., US 2002/0039348 A1 filed 2000-09-29; US 2002/0186667 A1 filed 2001-06-07; US 2009/0316571 A1 filed 2008-06-20). None has an earlier § 102(e) filing date. They therefore cannot be used in the § 103 combination, and I do not rely on them for the anticipation/obviousness mapping. I use them only as background evidence that (a) the field was crowded and (b) the claimed behaviors are what a ring engineer would routinely implement. The same is true of the Cisco SRP/IPS product documentation and RFC 2892 (Aug. 2000) found in search — highly probative of what the SRP "Intelligent Protection Switching" behavior was, but post-dating the priority date.

Contradiction check: nothing in these search results contradicts the previously generated summary sections. The bibliographic data (Cisco assignee, 1998 priority, expired lifetime) is consistent.

3. Level of ordinary skill in the art (PHOSITA)

A person of ordinary skill as of April 1998 would have a bachelor's degree in electrical engineering or computer science (or equivalent) plus 2–3 years of experience in data/telecom networking, and would be familiar with:

• SONET/SDH framing, line overhead, and the K1/K2 APS byte protocol;
• BLSR / UPSR ring protection switching, including wrap, squelch, and Wait-to-Restore;
• the standard APS request hierarchy and its pre-emption behavior; and
• packet ring MAC protocols (FDDI, Token Ring, and the emerging SRP/Dynamic Packet Transport work).

This is a routine level of skill; the APS protocol was a published standard by 1995–96, so the PHOSITA had the entire body of SONET protection-switching knowledge at hand.

4. Single-reference § 103: GR-1230-CORE (+ T1.105.01) maps most of the claims

Because the claims are drafted as functionally redundant apparatus/method/system/medium versions of a small set of rules, the four statutory families rise and fall together. Mapping (independent claims bolded):

Conclusion for § 4: For the independent claims 1, 2, 24, 26, 34, 51, 52, 60, 64 and dependent claims 4, 6, 8–14, 16–21, 27–33, 40–44, 46–49, 53, 57, 59, 61, the substance is disclosed by GR-1230-CORE in view of T1.105.01. Several (e.g., claim 10's hierarchy, claims 11–13's co-existence rules, claims 14's first-come resolution, claim 26/51's wrap + dual-path signaling) are so close that they are arguably anticipated under § 102(b), and at minimum obvious under § 103.

5. Explicit combinations and motivations to combine

5.1 Combination 1 — GR-1230-CORE + ANSI T1.105.01-1995

Why a PHOSITA would combine: T1.105.01 is the American National Standard for SONET Automatic Protection Switching; GR-1230-CORE is Bellcore's generic criteria implementing that standard for BLSR equipment. GR-1230 expressly builds on the APS protocol and the K1/K2 format of the ANSI standard (iterated in the K-byte-format discussion of US 2002/0087733 A1, which cites "the GR-1230 standard"). Combining a standard with its implementing criteria is not a § 103 "combination" at all — it is using the same body of prior art in the same field for the same purpose. Expectation of success is near certainty because GR-1230 is, by design, a more specific disclosure of the same protocol.

Result: Renders obvious claims 1, 2, 8–20, 24, 26, 34, 37, 38, 43–47, 51, 52, 54, 55, 60, 64.

5.2 Combination 2 — GR-1230 + T1.105.01 + U.S. 6,314,110

Why combine: The '210 patent's asserted advantage is applying the protection protocol to a packet ring that eliminates the SONET ADM layer while retaining fast protection. The '110 patent (same inventors) squarely discloses the SRP packet ring: two counter-rotating (inner/outer) rings, nodes with MAC-layer interfaces, control packets propagated in the direction opposite the data, and priority classes (see also Cisco's IEEE 802 SRP materials and RFC 2892, which confirm SRP ran on inner/outer counter-rotating rings with control messages opposite the data). A PHOSITA seeking to add survivability to the SRP ring had both the motivation (SRP's own stated goal of "fast protection and restoration against fiber and node failures") and the roadmap (the well-known SONET APS protocol) to implement APS signaling as SRP control packets.

Result: Supplies the "APS packets … on inner and outer rings" and packet-field limitations of claims 3, 4, 39, 40, 56, and the packet-ring context for all remaining claims. The combination is a predictable layering of a known protection protocol onto a known packet ring transport.

5.3 Combination 3 — GR-1230 + T1.105.01 + ('110) + ordinary design choice, for the residual limitations

• Claim 3/39/56 ("user-configurable" short/long periods to reduce steady-state traffic): The APS standard itself distinguishes a steady state (resend idle) from a switching state (send requests); making the two refresh intervals user-configurable and lengthening the steady-state interval to save overhead is the routine, predictable optimization an engineer applies to any periodic keep-alive/APS message (the same reasoning used for OSPF/STP hello timers). Under KSR, this is a "predictable variation" of the disclosed timing behavior. Cisco's later SRP documentation confirms exactly this design (an srp ips timer with a default of 1 s, and a WTR timer), corroborating that it was the natural implementation.
• Claim 25 (idle time vs. protection time keyed to an incomplete wrap): This is the ANSI/GR-1230 steady-state-vs-switching distinction expressed as two timer values. No new mechanism is claimed.
• Claim 22/50 (neighbor changed → WTR = 0): The patent itself admits the problem this solves (adding/removing a node). A PHOSITA implementing the SONET WTR state on a ring that supports node insertion would predictably reset the WTR timer when the neighbor identity (itself carried in the K-byte node-ID field per GR-1230 R6-72) changes, because holding a wrap for a neighbor that no longer exists serves no purpose. This is design-choice obviousness with a clear motivation.
• Claims 15/33/45 (predetermined-ring tie-break): GR-1230/T1.105.01 already teach deterministic tie-breaking of equal requests; selecting a predetermined one of the two rings (e.g., outer) as the tie-breaker is one of a small, finite set of predictable alternatives, rendering it obvious to try.

5.4 Secondary references available in the record (context/corroboration only)

• US 2002/0087733 A1 and JP 4036652 B2 (both later than the priority date) expressly describe using the K1/K2 source/destination node ID to identify the adjacent node and use short/long path to determine whether the ID is source or destination. They corroborate the claims-20/48/58/62 concept but are not § 103 prior art here.
• US 5,467,352 (Cidon) (cited as background in the '110 patent) shows spatial/local-reuse ring arbitration — again context, and earlier than 1998-03-06, so it would be available, but it is directed to bandwidth, not protection.

6. Why the claims are nonetheless likely non-anticipated on the exact form (but obvious)

The claims recite an apparatus ("a first node operable to…"), packets ("automatic protection switching (APS) packets"), and software in a computer-readable medium — statutory forms chosen to capture the packet-ring implementation. GR-1230/T1.105.01 describe a bit-oriented K1/K2 byte protocol in SONET line overhead, not "APS packets." That formal difference is the most plausible reason the examiner allowed the case over the two cited standards, and it is precisely the kind of difference § 103 is designed to bridge: replacing a byte-oriented APS channel with a packet-carried APS channel on a packet ring was an obvious, predictable implementation once the SRP packet ring existed (again, the '110 patent), and the specification itself concedes the underlying protocol is the SRP/APS protocol.

7. Claim-by-claim vulnerability summary

8. Rebuttal of potential non-obviousness arguments

• "No topology map needed" (the patent's stated advantage): This is a result of the single-hop, neighbor-addressed signaling scheme, not a claimed structural feature of most claims. The K-byte/APS scheme of GR-1230 is already a neighbor-addressed, topology-map-free mechanism (R6-72: K bytes are always destined to the adjacent node). Where the patent's independent claims don't recite "no topology map," the advantage is entitled to little patentable weight; where it is implied (claims 20/48/58/62), GR-1230's node-ID-in-K-byte mechanism supplies it.
• "Rings can be merged automatically": The specification's own claim 22/WTR behavior is the mechanism, and it is a design choice over the SONET WTR state. No unexpected result is demonstrated.
• Secondary considerations: I found no evidence in the record (and none in the previously generated litigation summary) of objective indicia — no litigation, no PTAB proceeding, no licensing/industry-acclaim evidence with a nexus to these claims. Absent such evidence, the Graham factor (4) does not rebut the strong prima facie case.

9. Caveats and evidentiary limits

1. I could not independently verify the full text of GR-1230-CORE Issue 3 (Dec. 1996) — the search returned the Issue 4 (Dec. 1998) table of contents and a Telcordia TOC extract. Issue 4 post-dates the April 1998 priority date by ~8 months; however, Issue 3 is the version cited on the face of the patent and predates it, and the K1/K2 semantics and priority hierarchy were stable across issues (as confirmed by the Cisco/Keysight summaries). A full-text check of Issue 3 is required before relying on specific paragraph cites.
2. ANSI T1.105.01-1995 was confirmed to address "linear 1+1 and 1:n topologies, and bidirectional line-switched ring network topologies" and to use "two bytes, K1 and K2" (GlobalSpec/ATIS abstract). I did not obtain the full clause text.
   3I treat all "Cited By" and "Families Citing" entries as non-prior-art unless they have a pre-1998-04-27 U.S. filing. The only qualifying third-party item I could identify is US 6,314,110 (filed 1998-03-06). If the intended "Prior Art section" refers to the examiner's two cited standards only, the analysis in §§ 4–5.1 stands unchanged.
3. Claim construction note: The independent claims use highly functional, result-oriented language ("operable to," "means for," "such that… if … then…"). Under Williamson v. Citrix (2015), several of the "means for" claims (54–61) may be construed under § 112(f); this does not change the § 103 outcome but affects the breadth of the corresponding structure.
4. Per the operating rules, I have interpreted US 6,820,210 and all reference numbers literally and have not auto-corrected any identifier.

Primary sources used

• US 6,820,210 B1 full text — https://patents.google.com/patent/US6820210/en
• Bellcore GR-1230-CORE TOC (Issue 4) — http://telecom-info.telcordia.com/ido/AUX/GR_1230_TOC.i04.pdf ; https://shop.standards.ie/en-ie/standards/gr-1230-core-issue-4-1064883_saig_tel_tel_2476551/
• ANSI/ATIS T1.105.01 (SONET APS) scope — https://standards.globalspec.com/std/[1215588](/patent/1215588)/0900105-01
• K1/K2 byte semantics (GR-1230) — https://www.keysight.com/tm/en/assets/9018-40820/user-manuals/9018-40820.pdf
• US 6,314,110 (SRP bi-directional ring; filed 1998-03-06) — https://patents.google.com/patent/US6314110 ; https://patentimages.storage.googleapis.com/e6/17/1d/4ad5fe2eeebe08/US6314110.pdf
• US 2002/0087733 A1 (K1/K2 source/destination node ID; GR-1230 R6-72) — https://patentimages.storage.googleapis.com/8b/42/76/7a1a99a1f68772/US20020087733A1.pdf
• Cisco SRP/IPS behavior (post-dating; corroborative only) — https://www3-realm.cisco.com/en/US/docs/routers/crs/software/crs_r4.1/interfaces/configuration/guide/hc41crsbook.pdf ; https://ieee802.org/1/files/public/docs1999/802_1_SRP.pdf