LEVEL 3 COMMUNICATIONS, LLC

Patent Trials and Appeals Board

May 7, 2020

14852519 - (D) (P.T.A.B. May. 7, 2020)

UNITED STATES PATENT AND TRADEMARK OFFICE
UNITED STATES DEPARTMENT OF COMMERCE
United States Patent and Trademark Office
Address: COMMISSIONER FOR PATENTS
P.O. Box 1450
Alexandria, Virginia 22313-1450
www.uspto.gov
APPLICATION NO. FILING DATE FIRST NAMED INVENTOR ATTORNEY DOCKET NO. CONFIRMATION NO.
14/852,519 09/12/2015 Robert Smith 0546-US-U1 4016
83579 7590 05/07/2020
LEVEL 3 COMMUNICATIONS, LLC
Attn: Patent Docketing
1025 Eldorado Blvd.
Broomfield, CO 80021
EXAMINER
NGUY, CHI D
ART UNIT PAPER NUMBER
2435
NOTIFICATION DATE DELIVERY MODE
05/07/2020 ELECTRONIC
Please find below and/or attached an Office communication concerning this application or proceeding.
The time period for reply, if any, is set in the attached communication.
Notice of the Office communication was sent electronically on above-indicated "Notification Date" to the
following e-mail address(es):
patent.docketing@centurylink.com
PTOL-90A (Rev. 04/07)
UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE PATENT TRIAL AND APPEAL BOARD
____________

Ex parte ROBERT SMITH and SHAWN MARCK
____________

Appeal 2018-007570
Application 14/852,519
Technology Center 2400
____________

Before ERIC B. CHEN, JAMES B. ARPIN, and MICHAEL J. ENGLE,
Administrative Patent Judges.

ARPIN, Administrative Patent Judge.

DECISION ON APPEAL
Appellant1 appeals under 35 U.S.C. § 134(a), the rejections of
claims 1–12 and 14. Final Act. 2.2 Claim 13 is cancelled. Appeal Br. 2.

1 “Appellant” here refers to “applicant” as defined in 37 C.F.R. § 1.42.
Appellant identifies the real party-in-interest as Level 3 Communications,
LLC. Appeal Br. 2.
2 In this Decision, we refer to Appellant’s Appeal Brief (“Appeal Br.,” filed
December 5, 2017), Supplemental Appeal Brief (“Supp. Appeal Br.,” filed
February 5, 2018), and Reply Brief (“Reply Br.,” filed July 16, 2018); the
Final Office Action (“Final Act.,” mailed September 22, 2017) and the
Examiner’s Answer (“Ans.,” mailed May 16, 2018); and the Specification
(“Spec.,” filed September 12, 2015). Rather than repeat the Examiner’s
findings and determinations and Appellant’s contentions in their entirety, we
refer to these documents. A hearing was held on April 17, 2020, and a
transcript (“Tr.”) of that hearing is included in the record.
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We have jurisdiction under 35 U.S.C. § 6(b).
We affirm.
STATEMENT OF THE CASE
Appellant’s claimed methods and systems relate to techniques for
mitigating distributed denial of service (DDoS) attacks on a network. Spec.
¶ 5. An address may be blocked temporarily if a request is classified as
originating from an attacker performing a DDoS attack, but analysis of
subsequent requests may result in unblocking the address. Id.; see id. at
Fig. 7 (flow chart depicting addition and removal of addresses from blacklist
based on classification of requests).
As noted above, claims 1–12 and 14 stand rejected. Claims 1 and 14
are independent, and claims 2–12 depend directly or indirectly from claim 1.
Supp. Appeal Br. 2–4 (Claims App.). Claim 1 recites “[a] method,” and
claim 14 recites “[a] system comprising: at least one processor; memory,
operatively connected to the at least one processor and storing instructions
that, when executed by the at least one processor, cause the system to
perform” the method, as recited in claim 1. Id. at 2, 4.
Claim 1, reproduced below with disputed limitations emphasized, is
representative.
1. A method comprising:
receiving, at a mitigation system, a plurality of requests for
one or more network resources to which the mitigation system is
providing a mitigation service;
identifying a first request of the plurality of requests as
occurring within a first observation cycle;
classifying the first request as a bad request based on one
or more properties of the first request;
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adding a first address associated with the first request to a
block list for blocking requests from the first address for a
specified time period;
identifying a second request of the plurality of requests as
being transmitted from the first address and as occurring within
a second observation cycle, the second request occurring within
the specified time period;
classifying the second request as a good request based on
one or more properties of the second request; and
removing, based on classifying the second request as a
good request, the first address from the block list prior to the
expiration of the specified time period, thereby allowing a future
request from the first address to be transmitted to the one or more
network resources.
Id. at 2 (emphasis added).
REFERENCES AND REJECTION
The Examiner relies upon the following references in rejecting the
claims:
Name3 Number Issued/Publ’d Filed
Saurel US 8,621,065 B1 Dec. 31, 2013 Oct. 23, 2008
Chebolu US 2005/0060412 A1 Mar. 17, 2005 Dec. 19, 2003
Afek US 2006/0212572 A1 Sept. 21, 2006 July 14, 2005
Weiser US 2013/0152153 A1 June 13, 2013 Dec. 7, 2011
Specifically, claims 1–3, 5, 6, 9, 11, and 14 are rejected as obvious over the
combined teachings of Saurel and Afek (Final Act. 3–8); claims 4, 7, 8, and
10 are rejected as obvious over the combined teachings of Saurel, Afek, and

3 All reference citations are to the first named inventor only.
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Chebolu (id. at 8–10); and claim 12 is rejected as obvious over the combined
teachings of Saurel, Afek, and Weiser (id. at 10–11).
Appellant contests the obviousness rejection of independent claims 1
and 14 and relies on the alleged deficiencies in the rejection of the
independent claims to overcome the rejections of dependent claims 2–12.4
Appeal Br. 4–11; Reply Br. 2–5. As noted above, the limitations of claim 14
mirror those of claim 1, and Appellant relies on the same contentions and
evidence in challenging the rejection of both independent claims. Appeal
Br. 4–9. Because we determine that affirmance of the rejection of
independent claim 1 is dispositive, except for our ultimate decision, we do
not discuss the merits of the rejection of claims 2–12 and 14 further herein.
We review the appealed rejection of independent claim 1 for error based
upon the issues identified by Appellant, and in light of the contentions and
evidence produced thereon. Ex parte Frye, 94 USPQ2d 1072, 1075 (BPAI
2010) (precedential). Arguments not made are waived. See 37 C.F.R.
§ 41.37(c)(1)(iv). Unless otherwise indicated, we adopt the Examiner’s
findings in the Final Office Action and the Answer as our own and add any
additional findings of fact for emphasis. We address the rejection of claim 1
below.

4 Appellant presents no contentions or evidence challenging the Examiner’s
rejection of claim 12. See Appeal Br. 4; Tr., 3:13–22. Claim 12 depends
from independent claim 1 via intervening claims 9–11. Appellant states that
claims 9–11 stand or fall with their base claim. Id. at 10–11. Thus, we also
treat claim 12 as standing or falling with its base claim.
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ANALYSIS
1. Obviousness of Claim 1 Over Saurel and Afek
As noted above, the Examiner rejects independent claim 1 as obvious
over the combined teachings of Saurel and Afek. Final Act. 3–5. The
Examiner finds that Saurel teaches or suggests almost all of the limitations,
as recited in claim 1. Id. at 3–4. However, the Examiner acknowledges that
Saurel “does not explicitly disclose removing based on classifying the
second request as a good request, the first address from the block list prior to
expiration of the specified time period.” Id. at 4.
Nevertheless, the Examiner finds
Afek discloses removing based on classifying the second request
as a good request, the first address from the block list prior to
expiration of the specified time period (¶ [0006]; i.e. blocking the
source for a period of time; [0089]; but if the packet contents are
found to be legitimate, removing the source from the blacklist
which is interpreted as removing the source from the blacklist
prior the period of time expired).
Id.
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Saurel’s Figure 4, including our annotations, is reproduced below.

Figure 4 depicts steps of a process for dynamically blocking requests,
including unblocking certain requests. Saurel, 1:61–63; see Final Act. 4
(citing Saurel, Fig. 4, to teach “removing the first address from the block list,
thereby allowing a future request from the first address to be transmitted to
the one or more network resources”); see also Saurel, 7:4–11 (“Systems and
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methods in accordance with other embodiments use dynamic blocking and
unblocking on a per-host basis for relatively short periods of time, or
monitoring periods of configurable length . . . .”).
Afek discloses, “[t]ypically, the guard device simply discards the
blocked packet, but alternatively, the guard device may analyze the packet
contents (and may even take action to deliver the packet or remove it from
the blacklist if the packet contents are found to be legitimate).” Afek ¶ 89
(emphasis added). Further, Afek discloses,
[i]f malicious traffic has not subsided, the guard device leaves
the source address on the blacklist, at a leave on blacklist step 80.
On the other hand, if the traffic has subsided for a sufficient
period of time, the guard device removes the source address from
the blacklist, at a remove from blacklist step 82.
Id. ¶ 90 (emphasis added), Fig. 4 (steps 78, 80, and 82).
The Examiner finds that a person of ordinary skill in the relevant art
would have had reason to combine the teachings of Saurel and Afek to
achieve the method of claim 1 “in order to allow legitimate network packets
to be processed while preventing malicious traffic.” Final Act. 5 (citing
Afek ¶¶ 4, 5, 89).
Appellant contends that the Examiner erred in rejecting claim 1 as
obvious over the combined teachings of Saurel and Afek for at least three
reasons. Appeal Br. 4–7; Reply Br. 2–5. For the reasons given below, we
are not persuaded of dispositive Examiner error.
First, Appellant contends that the Examiner acknowledges Saurel does
not teach or suggest removing based on classifying the second request as a
good request, the first address from the block list prior to expiration of the
specified time period. Reply Br. 2 (citing Final Act. 4).
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However, as noted above with respect to Saurel’s Figure 4, Saurel
discloses:
Systems and methods in accordance with other
embodiments use dynamic blocking and unblocking on a per-
host basis for relatively short periods of time, or monitoring
periods of configurable length, which can be effective in
preventing most attacks while not significantly affecting the user
experience for any genuine user that might inadvertently,
unintentionally, or innocently exceed a threshold for one of the
specified dimensions.

Saurel, 7:4–11 (emphasis added); see Tr., 10:2–13:22. Appellant contends
that Afek discloses removing the packet received from the same source and
does not teach or suggest removing the source, i.e., the address from the
blacklist. Appeal Br. 5; Reply Br. 3. In particular, Appellant contends that
the “it” in Afek’s paragraph 89 refers to unblocking the packet, not the
address. Appeal Br. 5; Reply Br. 3.
The Examiner finds, however, that Afek discloses, “[o]n the other
hand, if the address of the packet is found on the blacklist, guard device 28
blocks the further transmission of the packet at the block step 70.” Ans. 12–
13 (quoting Afek ¶ 89 (emphasis added)); see Afek, Abstract (“A
determination is made, by analyzing the first data packet, that the first data
packet was generated by a worm. In response to the determination, a second
data packet sent over the network from the source address is blocked.”
(emphasis added)), ¶ 90 (“the guard device removes the source address from
the blacklist” (emphasis added)). Consequently, we are persuaded, given
Saurel’s teaching of dynamic blocking and unblocking of addresses and
Afek’s teaching that the address can be the basis for blocking and
unblocking the packet, that Saurel and Afek together teach or suggest
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blocking an address by adding the address to a “block list” or unblocking or
removing the address from the “block list.”
Second, even if Afek teaches or suggests removing the source address,
Appellant contends that Afek does not teach or suggest removing the source
address “prior to expiration of the specified time period.” Appeal Br. 7;
Reply Br. 2–3. The Examiner finds, however, that Afek discloses, “[o]nce
the guard system detects a suspicious packet or traffic pattern, it may block
all or a portion of the packets from the same source for a period of time or
take other preventive action.” Ans. 13–14 (quoting Afek ¶ 6 (italics and
underlining added)). Thus, the Examiner finds that Afek is not limited to
waiting out a time period, but broadly discloses “other preventive actions.”
Id.; see Afek ¶ 90 (“The guard device typically determines that an attack has
concluded by detecting whether traffic from the source has subsided for a
certain period of time, at a traffic subsidence check step 78. If malicious
traffic has not subsided, the guard device leaves the source address on the
blacklist, at a leave on blacklist step 80. On the other hand, if the traffic has
subsided for a sufficient period of time, the guard device removes the source
address from the blacklist, at a remove from blacklist step 82.” (emphases
added)). Saurel teaches that the source of requests can be blocked for a
period of time if a threshold is exceeded. Saurel, 2:13–26, 2:31–34, 2:49–
57, 2:65–3:1, 8:25–28. However, as noted above, Saurel also teaches
“dynamic blocking and unblocking on a per-host basis for relatively short
periods of time, or monitoring periods of configurable length.” Id. at 7:5–7.
Such dynamic blocking and unblocking can limit the effect of DDoS attacks
on the genuine user experience caused by an inadvertent, unintentional, or
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innocent violation of a threshold for one of the specified dimensions. Id. at
7:7–11; see Tr., 19:5–20:4. Further, Saurel explains:
An administrator or other authorized person or process also
specifies or otherwise selects the length of a monitoring period
to be used to dynamically monitor and/or block requests 404. As
discussed above, an appropriate period such as two minutes can
be specified that allows for sufficient data collection while
substantially preventing damage due to excessive requests. This
period can vary by system, environment, process, and other such
dimensions, and can be determined before receiving requests
and/or adjusted or set after a period of receiving requests and
monitoring data.
Saurel, 7:59–8:2 (emphases added). Thus, we understand Saurel to teach
that dynamic blocking and unblocking allows the duration of blocking to be
optimized, e.g., minimized, to limit the effects of blocking on the genuine
user.5 See id. at 7:8–9; Tr., 16:7–18. Given Afek’s teaching that the guard
device may unblock a source address upon determining when an attack has
subsided “for a certain period of time” or “for a sufficient period of time,”
we are persuaded that the Examiner has shown that Saurel and Afek together
teach or suggest removing the address from the blocking list “prior to the
expiration of the specified time.” Ans. 11–14; see Saurel, 7:4–11; Afek
¶¶ 6, 89, 90. In particular, if malicious traffic is detected and an address is
added to the blacklist, the combination of Saurel and Afek would unblock
the address when either (A) a certain amount of time has passed since the
beginning of the attack, as in Saurel (i.e., the claimed “specified time

5 For example, a relevant definition of the adjective “dynamic” is
“[o]ccurring immediately and concurrently. The term is used in describing
both hardware and software; in both cases it describes some action or event
that occurs when and as needed.” MICROSOFT COMPUTER DICTIONARY, 181
(5th ed. 2002) (emphasis added).
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period”) or (B) a shorter amount of time has passed since the end of the
attack, as in Afek (i.e., the claimed “prior to the expiration of the specified
time period”).
Third, Appellant contends Saurel teaches away from its combination
with Afek. Appeal Br. 7; Reply Br. 3–5. In particular, Appellant contends
Saurel relies on the frequency of requests, not their content, but Afek relies
on content. Appeal Br. 7; Reply Br. 3–5; see Saurel, 8:35–46 (frequency);
Afek ¶ 70 (content).
A reference may be said to teach away when a person of ordinary
skill, upon reading the reference, would be discouraged from following the
path set out in the reference, or would be led in a direction divergent from
the path that was taken by the applicant. In re Gurley, 27 F.3d 551, 553
(Fed. Cir. 1994). “The fact that the motivating benefit comes at the expense
of another benefit, however, should not nullify its use as a basis to modify
the disclosure of one reference with the teachings of another. Instead, the
benefits, both lost and gained, should be weighed against one another.”
Winner Int’l Royalty Corp. v. Wang, 202 F.3d 1340, 1349 n.8 (Fed. Cir.
2000). However, “[a] reference does not teach away . . . if it merely
expresses a general preference for an alternative invention[.]” DePuy Spine,
Inc. v. Medtronic Sofamor Danek, Inc., 567 F.3d 1314, 1327 (Fed. Cir.
2009).
We are not persuaded that Saurel teaches away from its combination
with Afek for two reasons. First, Afek discloses, “[t]he guard device may
determine that the traffic from a given source address is suspicious, based on
the content or statistical properties of the traffic, for example.” Afek ¶ 7
(italics and underlining added). Thus, Afek is not limited to identifying
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suspicious traffic based on content. Specifically, Afek explains, “[i]n a
‘conventional’ massive-bandwidth attack, the source of the attack may be
traced with the help of statistical analysis of the source Internet Protocol
(IP) addresses of incoming packets.” Id. ¶ 3 (emphasis added). Second,
claim 1 recites that the nature of the requests is determined from their
“properties.” Supp. Appeal Br. 2 (Claims App.). The Specification explains
that such properties may reflect either the content or the source of the
request. See Spec. ¶ 22 (“The analysis of a request includes determining a
network resource being requested. Other examples of a property of the
request are the user agent string of a browser that one or more requests came
from.”). Nevertheless, neither the claim language nor the Specification
strictly limits what those “properties” are. See Spec. ¶ 52 (“[T]he first
request is classified as a bad request based on one or more properties of the
first request. The classification can be based on various criteria, e.g., as
described herein and in U.S. Patent Application No. 13/458,1296.”
(emphasis added)). Consequently, we do not find Appellant’s contention
persuasive of dispositive error.
We are not persuaded that the Examiner erred in rejecting claim 1 as
obvious over the combined teachings of Saurel and Afek. For the same
reasons, we are not persuaded that the Examiner erred in rejecting claim 14

6 Although Appellant does not incorporate the disclosure of U.S. Patent
Application No. 13/458,586 by reference, this application was published as
Patent Application Publication No. US 2013/0291107 A1, on October 31,
2013, before the filing date of the instant application. However, Appellant
does not specify the portion of the application, upon which Appellant relies
to teach the “criteria.”
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as obvious over the combined teachings of Saurel and Afek. Consequently,
we sustain the obviousness rejection of claims 1 and 14.
2. Dependent Claims 2–12
Each of claims 2–12 depends directly or indirectly from independent
claim 1. Supp. Appeal Br. 2–4 (Claims App.). As noted above, Appellant
challenges the rejections of dependent claims 2–12 for the same reasons as
their base claim. See id. at 10–11. Because we are not persuaded the
Examiner erred with respect to the obviousness rejection of claim 1, we also
are not persuaded the Examiner erred with respect to the obviousness
rejections of claims 2–12. For this reason, we sustain the rejections of those
claims.
DECISIONS
1. The Examiner did not err in rejecting claims 1–3, 5, 6, 9, 11, and 14 as
obvious over the combined teachings of Saurel and Afek.
2. The Examiner did not err in rejecting claims 4, 7, 8, and 10 as obvious
over the combined teachings of Saurel, Afek, and Chebolu.
3. The Examiner did not err in rejecting claim 12 as obvious over the
combined teachings of Saurel, Afek, and Weiser.
4. Thus, on this record, claims 1–12 and 14 are unpatentable.
CONCLUSION
For the above reasons, we affirm the Examiner’s decision rejecting
claims 1–12 and 14.

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In summary:
Claims Rejected 35 U.S.C. § References Affirmed Reversed
1–3, 5, 6, 9, 11,
14
103 Saurel, Afek 1–3, 5, 6, 9,
11, 14

4, 7, 8, 10 103 Saurel, Afek,
Chebolu
4, 7, 8, 10
12 103 Saurel, Afek,
Weiser
12
Overall
Outcome
1–12, 14
No time period for taking any subsequent action in connection with
this appeal may be extended under 37 C.F.R. § 1.136(a)(1)(iv).

AFFIRMED