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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Method for detection of the modified DDoS cyber attacks on a web resource of an Information and Telecommunication Network based on the use of intelligent systems</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Svitlana Onyshchenko</string-name>
          <email>s07onyshchenko@gmail.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Olena Haitan</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Alina Yanko</string-name>
          <email>al9_yanko@ukr.net</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Yurii Zdorenko</string-name>
          <email>zdorenkoviti@gmail.com</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oleksandr Rudenko</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>National University «Yuri Kondratyuk Poltava Polytechnic»</institution>
          ,
          <addr-line>Pershotravneva Avenue 24, Poltava, 36011</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Web services hosted in Information and Telecommunication Networks (ITNs) require reliable protection against cyber attacks. Most modern information services are characterized by increased requirements to ensure availability. One of the negative types of cyber influence in ITN is denial-of-service attacks (DDoS). Existing approaches for detecting attacks of this class are primarily based on classical signature analysis, and may also be based on the use of artificial intelligence at the current state of information technology development. However, existing approaches to implementing detection systems do not take into account the potential modification of cyber attacks, which makes their detection challenging. Therefore, it is proposed to use intelligent systems to improve the recognition of modified cyber impacts aimed at denial of service of a web service in ITN. These systems should be configured based on information about the level of traffic anomalies and data on the individual behavioral characteristics of a web resource.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Information and Telecommunication Network</kwd>
        <kwd>attack</kwd>
        <kwd>availability</kwd>
        <kwd>denial of service</kwd>
        <kwd>artificial intelligence</kwd>
        <kwd>neuro-fuzzy system 1</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>The development of new electronic services requires compliance with the security
requirements for the hosting</p>
      <p>web resources, including ensuring data integrity,
confidentiality, and availability. Availability is a crucial indicator of a web resource</p>
      <p>0000-0002-6173-4361 (S. Onyshchenko); 0000-0002-7228-9937 (O. Haitan); 0000-0003-2876-9316
(A. Yanko); 0000-000L-5649-771X (Y. Zdorenko); 0000-0002-7110-0653 (O. Rudenko)</p>
      <p>
        © 2024 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
security. The inability to access a resource at the appropriate time may result in negative
consequences. Therefore, ensuring the availability of web resources is an urgent task [
        <xref ref-type="bibr" rid="ref1 ref2">1,
2</xref>
        ]. Recent statistics indicate an increase in denial-of-service and availability attacks on
web resources. Thus, the class of DDoS attacks is at the top of the list of methods of cyber
interference in the operation of web services. Denial-of-service attacks can have
distributed sources of negative influence and a slow, time-delayed profile [
        <xref ref-type="bibr" rid="ref2 ref3">2, 3</xref>
        ]. This
indicates that the attackers are trying to hide the signs of an attack until a certain point in
time and disguise malicious traffic as normal [
        <xref ref-type="bibr" rid="ref2 ref4">2, 4</xref>
        ].
      </p>
      <p>
        Modification of DDoS attacks on a web resource should not affect the ability of
detection systems to recognize such malicious activity. To protect web resources, it is
crucial to use an attack detection system with the appropriate settings of the detection
mechanisms [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. Early detection of signs of cyber attacks aimed at denying service to web
resources in ITN is an important component of this protection.
      </p>
      <p>
        The classic implementation of attack detection systems necessarily includes the use of
signature analysis methods which determine the presence or absence of an attack by
comparing traffic telemetry indicators with known signatures [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]. However, modern
attack detection systems must also be able to operate effectively against new and modified
attacks. Signature detection methods do not allow ensuring this.
      </p>
      <p>
        An important factor in evaluating attack detection systems is the absence of false
positives. False positives can lead to erroneous preventive actions, such as blocking traffic
from certain users, increasing the response time of a web resource, or reducing the rating
of a web resource, etc. Therefore, modern attack detection systems should be based on
intelligent approaches that take into account the level of traffic abnormality and are able
to quickly learn and adapt to new conditions. The implementation of such systems is
currently possible on the basis of artificial intelligence methods [
        <xref ref-type="bibr" rid="ref10 ref7 ref8 ref9">7, 8, 9, 10</xref>
        ]. Nevertheless,
the presence of data on a high level of traffic abnormality when determining the cyber
influence may not always indicate the presence of an attack. For instance, a high level of
abnormality may be observed without malicious actions of users, but be caused by a
combination of random factors. Each web resource operates within a specific segment of
the ITN and has its own individual features, which are determined by the stack of network
protocols utilized, characteristics of the traffic (average request intensity, rate of change in
intensity, etc.), regional features, time of day, etc. These factors can influence the overall
traffic profile of a given segment and can be used to analyze its abnormality. Therefore, it
is crucial to correctly configure the parameters of the attack detection system, taking into
account the specified conditions of the web resource within a particular ITN. The data
obtained in this way about the level of traffic abnormality can be utilized to further decide
on the presence of an attack. The utilization of this indicator in the subsequent stages of
detecting modified denial-of-service attacks will allow for the necessary threat analysis to
be conducted in time, thus enabling the implementation of preventive measures.
      </p>
      <p>
        An important factor in evaluating attack detection systems is the absence of false
positives. False positives can lead to erroneous preventive actions, such as blocking traffic
from certain users, increasing the response time of a web resource, or reducing the rating
of a web resource, etc. Therefore, modern attack detection systems should be based on
intelligent approaches that take into account the level of traffic abnormality and are able
to quickly learn and adapt to new conditions. The implementation of such systems is
currently possible on the basis of artificial intelligence methods [
        <xref ref-type="bibr" rid="ref10 ref7 ref8 ref9">7, 8, 9, 10</xref>
        ]. Nevertheless,
the presence of data on a high level of traffic abnormality when determining the cyber
influence may not always indicate the presence of an attack. For instance, a high level of
abnormality may be observed without malicious actions of users, but be caused by a
combination of random factors. Each web resource operates within a specific segment of
the ITN and has its own individual features, which are determined by the stack of network
protocols utilized, characteristics of the traffic (average request intensity, rate of change in
intensity, etc.), regional features, time of day, etc. These factors can influence the overall
traffic profile of a given segment and can be used to analyze its abnormality. Therefore, it
is crucial to correctly configure the parameters of the attack detection system, taking into
account the specified conditions of the web resource within a particular ITN. The data
obtained in this way about the level of traffic abnormality can be utilized to further decide
on the presence of an attack. The utilization of this indicator in the subsequent stages of
detecting modified denial-of-service attacks will allow for the necessary threat analysis to
be conducted in time, thus enabling the implementation of preventive measures.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Problem formulation</title>
      <p>In modern ITN, ensuring the availability of web services is one of the priority tasks.
Systems for detecting attacks on the availability of web resources should also include
signature methods that need to be updated when new attacks are detected. Nevertheless,
the utilization of signature-based systems alone is insufficient for the detection of new and
even slightly modified DDoS attacks prior to the update of signatures.</p>
      <p>
        The implementation of new approaches based on intelligent traffic abnormality
detection systems necessitates the consideration of various factors, with the possibility of
periodic retraining of such systems. It should be borne in mind that a high level of
abnormality does not always indicate an attack [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. In this case, blocking the hosts from
which traffic with signs of abnormality is coming may result in a loss of trust in the web
resource, an increase in response time to user requests, and, as a consequence, a decrease
in the ratings of the web service in the future. Therefore, existing approaches for detecting
modified distributed denial-of-service attacks need to be improved.
      </p>
      <p>
        One of the priority ways for this is the development and multi-stage application of
intelligent systems based on fuzzy inference systems. Such systems can be used both for
the analysis of anomalies based on traffic telemetry, and in the subsequent stages of attack
detection (classification) using the behavioral characteristics of the web resource (for
example, changes in the load level of the host's resources, changes in the number of return
requests, and others). One of the most effective methods for achieving this objective is to
develop and implement intelligent systems based on fuzzy inference systems in a
multistage process [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. Such systems can be used for both the analysis of abnormalities based
on traffic telemetry and the subsequent detection (classification) of attacks using the
behavioral characteristics of a web resource (changes in the level of host resource
utilization, changes in the number of return requests, etc.) [
        <xref ref-type="bibr" rid="ref10 ref13">10, 13, 14</xref>
        ].
      </p>
      <p>
        It is assumed that the application of intelligent systems will facilitate the early
detection of modified attacks and significantly improve the availability of web resources in
ITN in conditions of modified cyber attacks of the DDoS class [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ].
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Related works</title>
      <p>
        The application of artificial intelligence methods to classify new or modified attacks is a
promising area [15, 16]. For example, the use of the mathematical apparatus of fuzzy sets
and neural networks to detect cyber influences is currently being studied in the work [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
The authors of [17, 18, 19] developed the FIS, which classifies attacks based on a set of
incoming traffic parameters.
      </p>
      <p>
        However, the approach described in the reviewed literature does not take into account
the peculiarities of new types of attacks. These features may be of a different nature
related to the characteristics of a particular ITN, host features, and may not fall under
anomalous data. A high level of traffic abnormality may not always indicate the presence
of an attack. So, in most cases, with data on high traffic abnormality, it is not possible to
accurately determine the presence of an attack until the moment it is completed and the
relevant signs of damage to the web resource are obtained. In such cases, the preventive
measures taken by a security expert may have negative consequences. Therefore, when
determining the class of attack, it is necessary to use advanced approaches based on
multistage analysis. The determination of the level of traffic abnormality in [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] can be based on
data on traffic characteristics, taking into account the IP addresses of senders and
receivers, ports of senders and receivers, the packets belonging to a specific protocol, the
presence of certain flags in the packet header, and the total number of incoming and
outgoing packets. These characteristics are used to find the level of traffic abnormalities in
the ITN [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. The coefficient of abnormality, which is determined in this case, can take
values in the range K={0;1}. At the second stage, the attack class can be determined based
on signature and intelligent methods. For this purpose, the obtained data on the level of
traffic abnormalities and behavioral information of the host are used. Data on the
behavioral characteristics of a host, such as operating system load level, number of
external network connections, and other characteristics, can be used for signature
analysis. However, signature analysis systems can detect an attack only if the measured
characteristics exactly match an existing pattern (signature). Even a slight modification of
the attack makes the use of signature-based methods ineffective. To detect modified
attacks, intelligent systems based on fuzzy logic can be used [
        <xref ref-type="bibr" rid="ref1">1, 19, 20, 21, 22, 23</xref>
        ]. This
will make it possible to detect existing attacks based on pre-trained fuzzy inference
systems even in the presence of minor changes (modifications) [19, 22, 24, 25, 26, 27].
Such systems, in general, have the appearance shown in Figure 1 [25].
      </p>
      <p>In such systems, value of the output variable K is determined based on the fuzzy
inference procedure based on values of the input variables z 1 , z 2 ,z 3 ,…,z n .</p>
      <p>
        The use of such systems for the classification of injection-type attacks is proposed in
[28]. To do this, values of the behavioral characteristics of a host obtained during the
operation of the ITN are fed to the FIS as input parameters. However, fuzzy inference
systems require periodic retraining. This mentioned approach [28] lacks mechanisms for
fast FIS training. It is possible to automate the learning process by combining the
mathematical apparatus of fuzzy logic and neural networks [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
      </p>
      <p>
        In the reviewed sources [
        <xref ref-type="bibr" rid="ref11">11, 29</xref>
        ], ANFIS was used to find various parameters of
information systems and showed its high efficiency in solving this problem. Therefore, this
paper proposes to use a system of this type to determine the presence of DDoS attacks at
several stages of intelligent analysis. It is anticipated that obtained in this way early
information about a potential DDoS attack will allow the implementation of preventive
measures to mitigate its impact and ensure the availability of the web resource in
conditions of cyber influence.
      </p>
    </sec>
    <sec id="sec-4">
      <title>4. Determination the level of network traffic abnormality on a web resource</title>
      <p>
        Based on the analysis, it is proposed to improve the proposed approaches to detection of
denial-of-service attacks by implementing several stages of applying fuzzy inference
systems. At the first stage, it is proposed to use an adaptive fuzzy neural system to
determine the level of traffic abnormalities, taking into account characteristics of the
traffic associated with a given ITN [
        <xref ref-type="bibr" rid="ref11">11, 24</xref>
        ].
      </p>
      <p>
        At the next stage, it is proposed to carry out measures to classify attacks based on
signature and intelligent analysis methods, taking into account the behavioral
characteristics of the host [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]. Since traffic with different characteristics can differently
affect the characteristics of the host on which the web resource is deployed, it is important
to take into account the behavioral characteristics of the host caused by the arrival of
traffic with different parameters. At the next stage, it is proposed that measures be taken
to classify attacks based on signature and intelligent analysis methods, taking into account
the behavioral characteristics of the host. Since traffic with different characteristics can
differently affect the characteristics of the host on which the web resource is deployed, it
is crucial to take into account the behavioral characteristics of the host resulting from the
arrival of traffic with different parameters.
      </p>
      <p>The process of studying a system can be represented as a sequence of discrete time
intervals of constant durationt i . During these intervals, the main characteristics of traffic
and behavioral characteristics of the host are measured.</p>
      <p>In general, such a mechanism for detecting a modified attack should include elements
for:




</p>
      <p>Obtaining and summarizing information about the characteristics of the traffic
coming to a web resource;
Determining the level of traffic anomalies;
Comparing of key traffic characteristics with signature characteristics;
Determining the key behavioral characteristics of the host;</p>
      <p>Making a decision about the existence of an attack.</p>
      <p>Figure 2 shows the block diagram of the system used to detect modified DDoS attacks,
based on the approach described above. The diagram involves several stages.</p>
      <p>
        The use of ANFIS to determine the level of abnormality results in finding a functional
dependence [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] in the form:
      </p>
      <p>K f (z1,z 2 ,...,zn ). (1)</p>
      <p>
        The internal structure of ANFIS is determined based on the chosen fuzzy inference
algorithm, the number of input variables and membership functions of each input variable
[
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. During the synthesis of ANFIS, it is proposed to use the first-order Sugeno algorithm
and three input variables with two membership functions each to determine the level of
abnormality. In this case, the structure of this system will have the form shown in Figure 3.
      </p>
      <p>It is proposed to use the following input values: z 1 is the number of incoming packets
during the observation interval t i , z 2 is the number of outgoing packets during the
observation interval t i , and z 3 is the rate of change of Moving Average of total packet
number during the specified observation period.</p>
      <p>Finding the correct output value for ANFIS depends on the accuracy of its training,
which is based on statistics obtained from traffic telemetry and observation data on the
behavioral characteristics of the host on which the web resource is deployed. One of the
most common training methods is a hybrid approach that combines gradient descent and
inverse error propagation method [30]. To generate training data, it is necessary to
observe the input variable values to obtain the desired output variable values. The
training data and neural weight settings of the proposed ANFIS for determining the level
of anomaly should be formed on the basis of traffic telemetry data in the ITN traffic
segment. The training matrix developed for this purpose has the following form:
 z i 1 z i 2 z i 3 K i 
z i 11 z i 12 z i 13 K i 1 
z i 21 z i 22 z i 23 K i 2 
 .... 
z i n 1 z i n 2 z i n 3 K i n 
(2)</p>
      <p>The matrix (2) was filled using data obtained from traffic telemetry in Information and
Telecommunication Network segment, as well as a series of traffic generation
experiments. The value of the input variable z 3 was calculated for each i-th time interval
using formula:</p>
      <p>z i 3  t 1ik  j iin z j 1 n z j 2  l kkn z l 1 n z l 2  (3)</p>
      <p>At the next stage, ANFIS will also be used to detect modified DDoS attacks. This
approach will facilitate the development of a method for detecting modified DDoS attacks
on a web resource.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Method for the detection of modified DDoS attacks based on the use of ANFIS</title>
      <p>This paper proposes a method for detecting modified cyber attacks based on the use of the
mechanism for intelligent analysis of traffic telemetry data and the obtained data on the
level of abnormality. The method involves the following steps:
1. Accumulate and structure statistical data on traffic characteristics in a defined
segment of ITN.
2. Synthesize the ANFIS architecture and its implementation on the ITN web resource
to determine the level of traffic abnormality.
3. Set up the ANFIS parameters by training based on traffic telemetry statistics in the
ITN, which has been collected over previous time intervals for the specified
abnormality levels.
4. Determine the level of traffic abnormality in the ITN segment using ANFIS.
5. Check the main characteristics of traffic with signature databases.
6. Accumulate and structure data on the behavioral characteristics of the host on
which the web resource is located.
7. Synthesize ANFIS to detect modified DDoS attacks, taking into account traffic
abnormalities and the behavioral characteristics of the web resource.
8. Conduct fuzzy inference based on ANFIS to detect a modified DDoS attack.
9. Make a decision on the presence of a DDoS attack on a web resource.</p>
      <p>
        To implement all the stages of the proposed method, it is necessary to develop
(synthesize) ANFIS for detecting modified attacks. For this purpose, we will also use the
method defined in [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
      </p>
      <p>The result of fuzzy inference based on the use of this ANFIS is finding a functional
dependence of the form (4) to determine the presence of a modified attack:
D  f (K ,x 2 ,..., x n ).
(4)</p>
      <p>As input values, we use the value of the abnormality coefficient K obtained at the
previous step for the (i-1) time interval. For the current time interval, the behavioral
characteristics of the host, on which the web resource is hosted, are calculated: x 1  K ,
x 2 , x 3 ,…, x n . The output value of such a system is an indicator of the presence of a
modified DDoS attack.</p>
      <p>In order to obtain a sufficient level of data accuracy when finding dependence (4), it is
suggested to use the 1st order Sugeno algorithm. The number of input values is three: K,
which represents the traffic abnormality coefficient, x 1 , which represents the host load
level during the current time interval and which is determined by formula (5), and x 2 ,
which represents the rate of change of the average moving level of the host load during the
specified observation period t i k and will be determined by the formula (6):
x i 1  1  т n j ,</p>
      <p>For each input value, it is sufficient to define two triangular membership functions
corresponding to fuzzy sets, designated as "small value" and "large value," as shown in
Figure 4.</p>
      <p>Then the proposed ANFIS will have the following structure (Figure 5):</p>
      <p>The shown ANFIS structure involves five layers. Each of the presented layers is
required for the fuzzy inference procedure to find an indicator of the presence of a
modified DDoS attack. The formed knowledge base of such ANFIS will contain 8 rules of
the following form (7)-(14):</p>
      <p>If K P1  and x 2 R1  and x 3 S 1  then D Y1 ,
If K P1  and x 2 R1  and x 3 S 2  then D Y 2 ,
If K P1  and x 2 R 2  and x 3 S 1  then D Y 3 ,
If K P1  and x 2 R 2  and x 3 S 2  then D Y 4 ,
If K P2  and x 2 R1  and x 3 S 2  then D Y 5 ,
If K P2  and x 2 R1  and x 3 S 1  then D Y 6 ,
If K P2  and x 2 R 2  and x 3 S 1  then D Y 7 ,
If K P2  and x 2 R 2  and x 3 S 2  then D Y8 ,
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
where P1 is the "small value" term of the input value K ; P 2 is the "large value" term of
the input value K ; R 1 is the "small value" term of the input value x 2 ; R 2 is the "large
value" term of the input value x 2 ; S 1 is the "small value" term of the input value x 3 ; S 2 is
the "large value" term of the input value x 3 ; Y1 ,Y 2 ,Y3 ,Y 4 ,Y 5 ,Y 6 ,Y 7 ,Y8 are the values of the
individual output of the fuzzy rule number k ,wherek  1,2...8 .</p>
      <p>The outcome of ANFIS training is the obtained expression for the membership
functions of the input variables:</p>
      <p>The training matrix, which was formed for this purpose, has the following form (21):
K  x 2p1;
K  x 1p 2;
K  x 2p 2;
The general procedure for using ANFIS to detect modified attacks is described below.</p>
      <p>The first layer of ANFIS according to expressions (15)-(20) performs fuzzification of
the values of the input variables K , x 2 , and x3 to find the values of the membership
functions of these variables.</p>
      <p>The second layer of ANFIS performs aggregation based on expressions (23)-(30):</p>
      <p>Q 8   2(K )  2(x 2 )  2(x 3 ) (30)</p>
      <p>The result of aggregation is then fed to the input of the third layer of neurons, where it
is normalized for k  1,8 .</p>
      <p>Data sets on the value of input variable and the expected value of the output variable
were recorded for the i 1..n time intervals of observation. The result of ANFIS training is
the adjustment of weights of the first layer neurons based on the obtained values of the
coefficients x 1p1 , x 2p1 , x 2p 2 , x 2p1 , x 1r 1 , x 2r 1 , x 1r 2 , x 2r 2 , x 1s 1 , x 2s 1 , x 1s 2 , x 2s 2 and
the adjustment of weights of the fourth layer neurons based on the obtained values of the
coefficients y 1k , y 2k , y 3k , y 4k for k 1..8 . Based on the obtained values of the
coefficients, the values of the individual outputs of the fuzzy rule number k ( k  1,8 ) are
determined according to the 1st-order Sugeno fuzzy inference algorithm using the
expression:</p>
      <p>Yk  y 1kK  y 2k x 2  y 3k x 3  y 4k
(22)
Q1  1(K )1(x 2 )1(x 3 )
Q 2  1(K )1(x 2 ) 2(x 3 )
Q 3  1(K ) 2(x 2 )1(x 3 )
Q 4   2(K )1(x 2 )1(x 3 )
Q 5  1(K ) 2(x 2 ) 2(x 3 )
Q 6   2(K )  2(x 2 ) 1(x 3 )
Q 7   2(K ) 1(x 2 )  2(x 3 )</p>
      <p>Q~k  8Q k .</p>
      <p>Q k
k 1</p>
      <p>The result of normalization is fed to the input of the fourth layer of neurons. In this
layer, the activation procedure is performed to determine the individual outputs of each
fuzzy rule by formula (22). Then, the neurons of this layer calculate the product of the
results of activation and normalization for k  1,8 according the formula:</p>
      <p>Ok Q~kYk . (32)</p>
      <p>The results of the operation of the fourth layer of ANFIS, determined by formula (30),
are fed to the input of the fifth layer of neurons, where defuzzification is performed to find
the value of the ouput value D . For this pirpose, the sum of the results of the operation of
the fourth layer of neurons is calculated according to the formula:</p>
      <p>8
D  O k (33)</p>
      <p>k 1</p>
      <p>The outcome of the fifth layer of ANFIS is finding of a precise value of the desired
output variable, which serves as an indicator of a modified DDoS attack.</p>
      <p>The data collection for the formation of training matrices (2) and (21) can be carried
out by telemetry of traffic in the ITN segment and observation of the behavioral
characteristics of the host. Such observations are carried out in a normal state of operation
of a particular ITN and in an abnormal state. An abnormal state of operation can be
ensured by creating artificial abnormal events similar to a DDoS attack or by observing a
real (confirmed) modified DDoS attack. To create artificial abnormal events, artificial
traffic generators are used from sources distributed throughout the network with an
abnormal number of requests (packets) directed to a web resource. It is also possible to
use accumulated traffic telemetry data with confirmation of a DDoS attack as training data.
Traffic telemetry data from DDoS attacks is also stored in publicly available databases,
such as KDD99, and can also be used to obtain training samples [18]. Values of the input
parameters calculated on the basis of traffic telemetry data according to formulas (3) and
(6), namely the values of the speed of change of the moving average of the total number of
packets on the web resource and the level of host load, are used to form matrices of the
form (2) and (21). The data obtained under these conditions is divided into two parts:
training and test. The data from the first set of matrices is fed to the input of neuro-fuzzy
systems for training. A hybrid method based on a combination of the back-propagation
method and gradient descent was selected as the training algorithm.</p>
      <p>Table 1 presents a list of coefficients obtained as a result of training neurons of the
fourth layer based on the observation of the behavioral characteristics of a host with a
web resource when creating artificial abnormal events in the ITN segment by generating
atypical traffic from various network nodes.</p>
      <p>Data from the second set of matrices (2) and (21) are used for testing after the training.
The result of successful training of ANFIS to detect a modified DDoS attack is the correct
determination of the values of the output variable D when using the test data set. The
number of training cycles is determined by estimating the permissible error in a series of
studies. As a testing environment for the presented ANFIS, it is proposed to use the Matlab
simulation environment [30].</p>
      <p>After training, the data from the second test part is fed to the ANFIS input, and the
output value is compared with the expected result. The permissible error is estimated in
order to determine the frequency of ANFIS retraining. It is proposed to retrain the ANFIS if
the number of matches is reduced to 98%.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusion</title>
      <p>The paper presents an approach for detecting modified DDoS attacks in ITM based on the
use of ANFIS. It is demonstrated that such an approach is a promising ways to detect
abnormalities in ITN. Neuro-fuzzy systems allow for the automation of the parameter
settings for fuzzy inference systems, the adaptation of these settings during operation, and
the automation of the process of developing rules for the knowledge base. The main stages
of the method for solving the problem of a modified DDoS attack detection in Information
and Telecommunication Networks are considered. It is shown that in addition to traffic
telemetry data, it is necessary to take into account the behavioral characteristics of the
host on which the web resource is deployed. Therefore, a feature of the synthesized
neurofuzzy attack detection system is the consideration and using of the traffic abnormality
coefficient, the level of host load, and the rate of change of the moving average of this value
as input variables. ANFIS allow obtaining the value of the network traffic abnormality
indicator, which provides a multi-stage attack detection procedure. We synthesize ANFIS
to detect modified DDoS attacks. Algorithms for training this system on test data were
selected and its effectiveness was investigated. The proposed method for detecting of
modified DDoS attacks will allow security administrators to receive early warning
information about modified threats in order to take the necessary measures to ensure the
availability of web resources.</p>
      <p>Further research should focus on generating statistics to effectively train the
neurofuzzy system and conducting research with a different set of input parameters to detect
modified DDoS attacks in various segments of the ITN.
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