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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>A. Melnyk);</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>network⋆</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Oleh Korkushko</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Andriy Melnyk</institution>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Catholic University in Ruzomberok Ruzomberok</institution>
          ,
          <addr-line>Hrabovská cesta 1A, 034 01 Ruzomberok</addr-line>
          ,
          <country country="SK">Slovakia</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Department of Clinical Engineering, Academy of Silesia</institution>
          ,
          <addr-line>40-555 Katowice</addr-line>
          ,
          <country country="PL">Poland</country>
        </aff>
        <aff id="aff3">
          <label>3</label>
          <institution>Ternopil Volodymyr Hnatiuk National Pedagogical University</institution>
          ,
          <addr-line>Maxyma Kryvonosa Street 2, 46027 Ternopil</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
        <aff id="aff4">
          <label>4</label>
          <institution>West Ukrainian National University</institution>
          ,
          <addr-line>Lvivska Street 11, 46001 Ternopil</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2026</year>
      </pub-date>
      <volume>000</volume>
      <fpage>0</fpage>
      <lpage>0000</lpage>
      <abstract>
        <p>This study presents a mathematical and knowledge-oriented framework for analyzing and optimizing the efficient and balanced operation of a university computer network. The growing complexity of higher education ICT infrastructures, the expansion of digital services, and the intensification of user activity require advanced modeling techniques capable of supporting data-driven management decisions. The proposed approach integrates mathematical modeling, performance analysis, and knowledge-based methods to evaluate structural balance, operational efficiency, and resource utilization within institutional networks. A key contribution of this work is the development of a dynamic load-distribution model for terminal cluster centers, which are responsible for processing high-intensity user requests in academic environments. The model incorporates temporal and structural characteristics of network traffic, adaptive balancing strategies, and knowledge-driven rules for predicting load fluctuations across distributed terminal clusters. This enables the system to reallocate computational resources in real time, prevent overload states, and maintain stable quality-of-service indicators under varying workloads. The results demonstrate that combining mathematical modeling with knowledge-oriented decision mechanisms significantly enhances network efficiency, reduces response delays, and ensures balanced utilization of computational and communication resources. The proposed framework can serve as a basis for designing intelligent management systems for university ICT infrastructures and contributes to the development of advanced methods for performance optimization in educational networks.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Mathematical modeling</kwd>
        <kwd>knowledge-oriented approach</kwd>
        <kwd>university computer networks</kwd>
        <kwd>network efficiency</kwd>
        <kwd>load balancing</kwd>
        <kwd>terminal clusters</kwd>
        <kwd>resource optimization</kwd>
        <kwd>knowledge-based systems</kwd>
        <kwd>performance analysis</kwd>
        <kwd>1</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>Modern corporate networks of higher education institutions are characterized by a high degree of
distribution, intensive traffic, and extensive use of terminal servers for providing access to
information resources, virtual laboratories, and educational services. Under such conditions,
ensuring reliable user identification and authentication, as well as maintaining uninterrupted
operation of network communication channels, becomes critically important. Most university
infrastructures rely on Kerberos-based technologies, which establish distributed authentication
systems and require consistent interaction among terminal servers [1–3].</p>
      <p>Despite the widespread adoption of terminal networks, several essential issues remain
unresolved. In particular, the optimal load distribution among terminal servers and the assurance
of communication channel survivability under failures, peak loads, or uneven resource utilization
constitute some of the most urgent challenges in the network infrastructures of modern
universities. Insufficient fault tolerance and ineffective load balancing may lead to prolonged
authentication delays, reduced service availability, and impaired performance of educational and
research platforms [4, 5].</p>
      <p>Therefore, the development of models, methods, and algorithms aimed at enhancing
communication channel survivability, optimizing the exchange of authentication information, and
enabling dynamic load distribution among terminal servers represents a relevant scientific task.
Addressing these issues will contribute to improving the resilience, scalability, and efficiency of
corporate networks in higher education institutions, in line with contemporary trends in the
development of secure and highly available information and communication systems [6, 7].</p>
    </sec>
    <sec id="sec-2">
      <title>2. Task Statement</title>
      <p>Corporate computer networks in higher education institutions extensively rely on terminal servers
and Kerberos-based infrastructure to provide user authentication and access to educational and
scientific services. In such systems, user groups are attached to specific terminal servers, which
interact with one another on a peer-to-peer basis and form a distributed authentication subsystem.
The reliability and efficiency of this subsystem depend on its ability to maintain minimal
authentication service time and preserve service availability even in the presence of server failures
[8, 9].</p>
      <p>In real operational environments, terminal servers may fail, become overloaded, or operate in
degraded mode. Under such conditions, users of failed servers must be promptly reassigned to
other functional servers, taking into account available resources, load levels, access policies,
network topology, switching costs, and performance constraints. At the mathematical level, this
problem is formulated as the redistribution of user groups among terminal servers while
minimizing the average service time and satisfying constraints related to flow intensities, memory
resources, security policies, and communication bandwidth [10].</p>
      <p>However, exhaustive enumeration of all possible redistribution variants is computationally
infeasible: the number of alternatives grows exponentially with the number of servers. Therefore,
solving this problem requires specialized methods for reducing the search space and developing
efficient optimization algorithms. Traditional mathematical models do not incorporate logical,
policy-based, and semantic dependencies among network components, which limits the practical
relevance of their outputs [11].</p>
      <p>At the same time, existing terminal network management systems do not employ semantic
technologies to represent knowledge about the infrastructure and thus cannot produce
contextaware redistribution decisions. Consequently, the research problem is to develop an integrated
knowledge-oriented model for load redistribution in terminal cluster centers, which combines: a
formal stochastic model of the terminal network; an ontology that captures structural, operational,
and policy constraints, an optimization algorithm that accounts for both numerical parameters and
semantic dependencies, semantic filtering methods based on SPARQL queries, KnowledgeRule
specifications, and logical reasoning.</p>
      <p>The objective of the study is to determine an optimal plan for reassigning users from failed
servers to operational servers while minimizing the average service time and switching cost under
technical and semantic constraints.</p>
    </sec>
    <sec id="sec-3">
      <title>Distribution of Terminal Cluster</title>
      <p>One of the key challenges in organizing communication channels among terminal servers in
corporate university networks is ensuring reliable identification and authentication of a closed
group of authorized users, (Fig. 1). In modern infrastructures, user identification and authentication
during the establishment of network communication channels are predominantly implemented
through Kerberos-based mechanisms built on the client–server paradigm [12–14]. According to
this approach, terminal networks are partitioned into Kerberos realms, each containing a dedicated
authentication server responsible for granting authorized users controlled access to approved
information resources.</p>
      <p>Terminal servers interact with each other through pairwise communication channels, forming a
distributed authentication system. These servers share a common secret key and exchange
authentication information required for validating user identities within the system. Each server
maintains a localized database that stores credentials and authorization attributes of legitimate
users.</p>
      <p>It should be emphasized that, despite the increasing interest in terminal-oriented network
technologies, numerous issues related to their practical organization, scalability, and reliability
remain insufficiently addressed [15]. One of the most significant challenges in this domain is the
development of efficient methods and algorithms aimed at improving the survivability of
communication channels. Such mechanisms must guarantee that authorized users retain timely
access to requested resources even under various failure scenarios, including partial server outage,
link degradation, or unexpected load surges [16, 17].</p>
      <p>To address these challenges, the modeling of dynamic load distribution among terminal cluster
centers becomes a critical research direction. At the initial stage of this modeling process, the
structure of the computer network is formally represented using an open stochastic network,
which enables the analytical description of probabilistic interactions, load fluctuations, and state
transitions occurring in distributed authentication environments.</p>
      <p>Let us assume that the set of terminal servers created within the computer network is denoted
by  = {1, 2, …, } and that to each server  a certain group of authorized users from the set  is
assigned. In other words, for each server  there exists a subset  ⊂  such that the family
{U i}in=1 forms a partition of , i.e.</p>
      <p>U ∩U j=∅ , i≠ j .</p>
      <p>
        i
(
        <xref ref-type="bibr" rid="ref1">1</xref>
        )
Each subset  consists of individual users  . Thus, we can write
n
U =∪in=1 U i , [U i ]=ni , ∑ ni=m , m&gt;n , (
        <xref ref-type="bibr" rid="ref2">2</xref>
        )
i=1
where  is the total number of authorized users and n is the number of terminal servers.
      </p>
      <p>Naturally, all servers from the set  perform identical authentication functions, since they
implement a unified security policy of the terminal network. As a performance criterion for the
operation of the communication channels during authentication, we consider 0, the average
service time of user authentication requests under the condition that all servers from S are fully
operational.</p>
      <p>Assume further that the terminal network is represented as an exponential open stochastic
network composed of a finite number of single-channel queuing systems. These systems form
service nodes characterized by a constant arrival intensity λ0, which does not depend on the
network state, at the output of the request source 0.</p>
      <p>Let the intensity λ0, be known and considered as a parameter of the network. Requests from the
source 0 enter the network with a constant probability 0 of being routed to the queuing system
(QS) . Requests served by QS  are then forwarded with a constant probability  to QS ,
 = 1, …,  or leave the network (for  = 0), i.e., are returned to the request source. Obviously, the
following normalization condition must hold: the sum of the routing probabilities from node 
over all possible destinations  = 0, 1, …,  is equal to one.</p>
      <p>We now consider the transformation of the input request flow with intensity λ0 into the input
flows of the constituent  of the network in the steady-state regime. Let  denote the
transmission (transformation) coefficient of the input request flow to the input of QS ,
quantitatively equal to the average number of occurrences of an arbitrary request from the
network input flow within the input flow of QS . Then the intensity of the input flow to QS  can
be expressed in terms of λ0 as</p>
      <p>λ i=α i iλ 0 .</p>
      <p>On the other hand, by definition, the fraction of clients from the subset  in the total intensity
λ0 can be expressed through the individual request intensities  of user  directed to the
server – QS . Extending this relation to all subsets ,  = 1, we obtain a set of relations connecting
the global input intensity λ0 with the input intensities λ of all  of the network.</p>
      <p>Since a lossless network is considered, the output intensities of the flows from  ,  = 1, …, 
coincide with the intensities of their input flows. The input intensity of the flow to  ,
 = 1, …, , is equal to the sum of the flow fraction arriving directly from the request source and the
fractions of flows routed from other  of the network according to the corresponding routing
probabilities.</p>
      <p>Taking into account the above relations and the equality λ = λ0, we transform the
corresponding balance equation into the following system of linear non-homogeneous algebraic
equations with respect to the transmission coefficients ,  = 1, …, , which has a unique solution.</p>
      <p>x (k )=⟨ x1(k ) , ... , xi (k ) , ... , xn n (k )⟩ ,
where () = 0 if server  is operational and () = 1 otherwise. It is known that the total
number of such state vectors is 2n. Among these vectors, we are not interested in the state
⟨0, 0, …, 0⟩, when all servers are operational, nor in the state ⟨1, 1, …, 1⟩, when all servers have
failed. In other words, we consider only the non-trivial states (),  = 1, …, , where = 2n - 2.</p>
      <p>The essence of the problem is as follows: the security administrator of the communication
channels, in the presence of failures of some servers corresponding to a state (), redistributes
their users among the operational servers, subject to certain constraints. For example, since these
servers may be geographically distributed, additional costs arise when redirecting users between
them.</p>
      <p>Assume that the cost required to switch user  from failed server  to an operational
server  in state () is denoted by C(ijk) ,  = 1, …, . Furthermore, let the memory capacity of
the network hardware on which the servers  are implemented be given by V imax ,  = 1, …, . The
actual memory volume required to host server  is denoted by   = 1, …, .</p>
      <p>To describe the redistribution of users of failed servers  under a given state vector () among
the functioning servers , we introduce the pseudo-Boolean variable (). Here, () = 1 if the
users from the set  of the failed server  are switched to server  for authentication in state (),
and () = 0 otherwise. Note that, for each state (), all users from  are connected to exactly
one functioning server.</p>
      <p>
        Based on the above considerations, as well as formulas (
        <xref ref-type="bibr" rid="ref2">2</xref>
        ) and (
        <xref ref-type="bibr" rid="ref4">4</xref>
        ), we obtain the following
optimization model:
      </p>
      <p>n
T k=∑ α (ik)t j(k)→min k =1 , N ,</p>
      <p>j=1
where, by applying the expressions for  and  for the states (), we obtain that:
α i (k )=[ n n j n
n i n n i
∑ λ kji+∑ ∑ λ ki X(ik) X(jk)
k j=1 i=1 ki=1
∑j=1 k∑j=1 λ k j+ ∑i=1 α (ik) λλ iij (1− x(ik)+ x(jk))
with the constraints:
t(jk)=</p>
      <p>(1− x(ik))
μ −{∑ λ k j+∑ [ ∑ λ ki x(ijk)+λ ij (1− x(jk))]}
n i n n i
kj=1 i=1 ki=1</p>
      <p>I =1 , n , j=1 , n , k =1 , N ,
n
∑ x(k) x(ik)=n−1 , j=1 , n , k =1 , N ,</p>
      <p>
        ij
i=1
(
        <xref ref-type="bibr" rid="ref5">5</xref>
        )
(
        <xref ref-type="bibr" rid="ref6">6</xref>
        )
(
        <xref ref-type="bibr" rid="ref7">7</xref>
        )
(
        <xref ref-type="bibr" rid="ref8">8</xref>
        )
(
        <xref ref-type="bibr" rid="ref9">9</xref>
        )
(
        <xref ref-type="bibr" rid="ref10">10</xref>
        )
(
        <xref ref-type="bibr" rid="ref11">11</xref>
        )
n
∑ x(k) x(ik)=1 , i=1 , n , k =1 , N ,
      </p>
      <p>ij
i=1</p>
      <p>n n i n
∑ ∑ ∑ c x(ijk) x(ik)≤C
i=1 k=1 j=1</p>
      <p>k =1 , N ,
n
∑ V x(k) x(ik)≤V mjax−V j , j=1 , n , k =1 , N ,</p>
      <p>i ij
i=1</p>
      <p>n n i
min [μ /α (jk)]&gt;∑ ∑ λ ki , j=1 , n , k =1 , N .</p>
      <p>
        i=1 ki=1
(
        <xref ref-type="bibr" rid="ref12">12</xref>
        )
      </p>
      <p>
        Constraint (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) implies that, when redistributing the users of failed servers  among the
functioning servers  under the state vector (), the total switching cost must not exceed the
predefined threshold . Inequality (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) imposes an upper bound on the input flow intensity λ0
under the condition that a steady-state regime exists in the exponential open stochastic network.
      </p>
      <p>
        As follows from formulas (
        <xref ref-type="bibr" rid="ref8">8</xref>
        )–(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ), the algorithm for solving the optimization problem belongs
to the class of discrete programming problems with pseudo-Boolean variables. Before developing a
practical algorithm suitable for real-world implementation in the design and operation of terminal
networks, we first evaluate the computational complexity associated with this model under full
enumeration of all possible variants.
      </p>
      <p>
        It is known that m faulty terminal servers can be selected from n servers in Cm different ways.
n
In this case,  -  servers remain operational. According to model conditions (
        <xref ref-type="bibr" rid="ref8">8</xref>
        )–(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ), the users of
each failed server must be reassigned to one of the ( - ) operational terminal servers. Clearly, for
a given number m of failed servers, the total number of possible variants ( − ) of redistributing
them among the ( - ) functioning servers is equal to
      </p>
      <p>Θ (n , m)=Cnm(n−m)⋅(n−m)⋯(n−m)=Cnm(n−m)m .</p>
      <p>
        Extending this formula to all values of mmm, where 1 ≤  ≤  - 1, we obtain the computational
complexity () of the model (
        <xref ref-type="bibr" rid="ref9">9</xref>
        )–(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ):
      </p>
      <p>
        n−1
u (n)=∑ Cnm(n−m)m . (
        <xref ref-type="bibr" rid="ref14">14</xref>
        )
      </p>
      <p>m=1</p>
      <p>It is evident that solving this problem by complete enumeration is practically infeasible [17].
Therefore, when solving such problems, one must aim at an efficient partial enumeration of a
comparatively small subset of feasible variants while implicitly pruning the remaining ones.</p>
      <p>
        This objective is addressed by the algorithm corresponding to model (
        <xref ref-type="bibr" rid="ref9">9</xref>
        )–(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ), which is based on
the branch-and-bound method and takes into account the specific structure of the problem under
consideration.
      </p>
      <p>
        Let us introduce the following notation:
(
        <xref ref-type="bibr" rid="ref13">13</xref>
        )
(
        <xref ref-type="bibr" rid="ref15">15</xref>
        )
      </p>
      <p>I k={i∣x(ik)=1}iJ k={i∣x(ik)}=0 ,
where  = {1, 2, …, }. Evidently,  =  =/ that is, the faulty servers form the set , and the
functioning servers form the complementary set .</p>
      <p>The branching tree is constructed as follows. The subset of the first level is formed by fixing the
assignment of the first server from  to different servers in : 1, 2, ||.</p>
      <p>Each set 1 contains all variants in which the first failed server in  is assigned to server 1 ∈ ,
while the assignments of the remaining failed servers are arbitrary.</p>
      <p>Similarly, the subset at the second level is formed by fixing the assignment of the second server
in  to different servers in . The set 1,2 contains all variants in which the first failed server is
assigned to server 1 ∈ , the second failed server is assigned to server 2 ∈ , and the assignments
of the remaining servers in  remain arbitrary, and so on.</p>
      <p>
        For each subset (i.e., each node of the branching tree), it is necessary to construct bounds of the
objective function (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) and of the corresponding constraints. The general expression for the
estimate of the objective function for the subset of variants 1, 2, , in this problem can be written
as: (1, 2, .., ), where (1, 2, .., ) denotes the estimate of the objective function for all variants
within the subset, with the first lll decision parameters fixed to 1, 2, .., , while for the remaining
parameters,  =  + 1,  + 2, …, | | , no specific assignment has yet been chosen.
      </p>
      <p>
        This estimate is considered valid only if the following feasibility conditions for the constraints
are satisfied:
jk 1 Ik jk
∑ ∑ Cmj X mj+min ∑ ∑ X(mk) X(mkj) Cmj≤C
j=1 m=1 m=1+1 j=1
jk 1 Ik jk
∑ ∑ V j+min ∑ ∑ V i X(mk) X(mkj)&lt;V mjax−V j ,
j=1 m=1 m=1+1 j=1
j=1 , J k ,
(
        <xref ref-type="bibr" rid="ref16">16</xref>
        )
minμ /α (ik)&gt;λ 0 .
      </p>
      <p>Based on the above formulas, the algorithm for solving the optimization problem is constructed
as follows (Fig. 2):</p>
      <p>Step 0. Initialization.</p>
      <p>Step 1. Input data. Enter the initial parameters: the number of servers nnn; the switching costs
of redirecting users from server  to server ,  ,  = 1, …, ; the maximum memory capacities of
the hardware hosting the servers, V mjax  = 1, …, ; the actual memory volumes of the servers,
  = 1, …, ; the probabilities of request transmission from server  to server ,  ,  = 1, …, ;
and compute the values 0 ,  = 1, …, .</p>
      <p>Step 2. Generation of the next state vector . Determine the sets of operational and failed
servers: 0 (operational) and : 1 (failed), respectively.</p>
      <p>Step 3. Selection of the next unassigned failed server from 1.</p>
      <p>Step 4. Computation of the “residual service intensity”. For each server in 0, compute its
residual service intensity, defined as the difference between the service intensity  and the sum of
request intensities from the server currently being considered and all failed servers already
assigned to it. If the request intensity of the selected failed server in 1 exceeds all residual service
intensities of servers in 0, proceed to Step 10. Otherwise, select the first server in 0 whose residual
service intensity exceeds the request intensity of the failed server. Record the pair (, ), where
 ∈ 1 is the failed server and  ∈ 0 is the selected operational server, into the assignment list.</p>
      <p>
        Step 5. Constraint verification. Check whether constraints (
        <xref ref-type="bibr" rid="ref11">11</xref>
        ) and (12 are satisfied for the
current partial assignment. If at least one constraint is violated, proceed to Step 10; otherwise
continue.
      </p>
      <p>Step 6. Check if the current failed server is the last element in 1. If so, proceed to the next step;
otherwise go to Step 10.</p>
      <p>
        Step 7. Solving the system of equations. Solve system (
        <xref ref-type="bibr" rid="ref11">11</xref>
        ) using the simple iteration method to
obtain , j = 1, …, n. Compute , j = 1, …, n, and the value  using formulas (
        <xref ref-type="bibr" rid="ref7">7</xref>
        ) and (
        <xref ref-type="bibr" rid="ref10">10</xref>
        ),
respectively. Since the denominator in formula (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) satisfies the convergence condition, the
iterative procedure converges.
      </p>
      <p>
        Step 8. Verification of condition (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ). If condition (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) is not satisfied, proceed to Step 10;
otherwise continue.
      </p>
      <p>Step 9. Update of the current best solution. If a previously computed value of  exists,
compare it with the newly obtained value . If  &lt;  , continue to the next step. Otherwise, or
if  has not yet been assigned, set  =  and store the corresponding server assignment.</p>
      <p>Step 10. Backtracking. Check whether backtracking is possible. Select the most recently
assigned pair from the assignment list. If the list is empty, backtracking is impossible; proceed to
Step 11. Otherwise, attempt to find another operational server to which the selected failed server
can be reassigned. If such a server is found, update the assignment and go to Step 4. If no such
server exists, remove the selected failed server from the assignment list and repeat Step 10.</p>
      <p>Step 11. Output of results for the current state. If a value  has been obtained, output the
corresponding optimal distribution of failed servers among operational servers. If no such value
exists for the given state vector , output a message stating that redistribution is impossible. If the
number of processed states is less than 2n - 2 increment the state index and return to Step 2;
otherwise proceed to Step 12.</p>
      <p>Step 12. Termination. The computational complexity () of the proposed algorithm is
significantly lower than the complexity () of the full enumeration method. As illustrated in Table
1, with an increasing number of servers, the efficiency of the algorithm — expressed as the
ratio ()/() — grows, which confirms its practical advantage for authentication processes in
terminal networks.</p>
      <p>
        It should be noted that the inclusion of constraints (
        <xref ref-type="bibr" rid="ref8">8</xref>
        )–(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) feasible optimal redistribution plan
exists for assigning failed servers to the operational ones. In such cases, immediate operational
measures must be applied to mitigate these situations. These measures may include relaxing the
constraints by increasing the memory capacity of the relevant hardware components, replacing
servers with more powerful units, or increasing the threshold value  in constraint (
        <xref ref-type="bibr" rid="ref12">12</xref>
        ).
      </p>
      <p>The use of the proposed algorithm makes it possible to construct an optimal redistribution plan
for assigning failed servers  to functioning servers  in the form of a matrix ∥()∥ This matrix
can serve as the basis for the decision-support functional block used by the security administrator
of the terminal network of a university’s corporate information system in emergency conditions.</p>
      <p>However, it should also be taken into account that a large number of Kerberos servers in the
network increases the volume of authentication information exchanged between them, which, in
turn, increases the overall load on the network.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Knowledge-Oriented Extension of the Model for Terminal Cluster</title>
    </sec>
    <sec id="sec-5">
      <title>Networks</title>
      <p>In order to enhance the flexibility, scalability, and intelligence of the mathematical model of
terminal cluster centers, it is advisable to integrate a knowledge-oriented approach whose central
element is the construction of an ontology of terminal cluster systems and the mechanisms of its
software interpretation. Unlike traditional models that operate exclusively with parametric
descriptions, the ontology provides a structured, formalized, and semantically consistent
representation of knowledge about the network, its behavior, constraints, and relationships
between components. As a result, the mathematical model gains the ability to operate not only
with flow intensities and cost values, but also with logical parameters, access policies, historical
data, and contextual characteristics [18, 19].</p>
      <p>The ontology of terminal cluster systems covers the fundamental elements of the infrastructure
and their semantic links (Fig. 3). The central concept is the “Terminal Server” as an object
characterized by a set of essential properties, including physical and logical resources,
computational capacity, architectural type, failure probability, connections to other servers, and its
role in authentication mechanisms. Each server is associated with the concept of “Memory
Resource”, which specifies both the maximum available volume and the actual volume required to
host authentication processes. The model also includes the concept of a “User Group”, which
aggregates sets of users attached to specific servers and supports semantic labeling of different
access profiles, priority levels, and request intensities. The state of each server is described by the
concept of “Operational State”, which allows the system to capture normal functioning, partial
degradation, or complete failure. All these elements are integrated into a structure that makes it
possible to track the interactions between them, including routes of authentication information
exchange, compatibility relations between servers, and dependencies between load and failure
probability.</p>
      <p>An important aspect of the ontological model is its ability to represent causal and semantic
dependencies that are difficult to formalize within a purely analytical framework [20 –23]. For
example, a server with a high load level or frequent failures is automatically regarded as a less
preferable candidate for load redistribution. Servers interconnected by high-speed communication
channels receive higher priority for authentication processes, which reduces delays and increases
the overall throughput of the network. Security policies such as the mandatory use of a server with
a higher trust level for certain categories of users can likewise be formalized within the ontology
and automatically applied when generating redistribution plans.</p>
      <p>The software interpretation of such an ontology enables machine-level exploitation of the
accumulated knowledge. By employing OWL and RDF standards, the ontology acquires a formal
structure that can be processed in a software environment while preserving logical consistency and
supporting automatic inference of new knowledge. Semantic queries expressed in SPARQL make it
possible to extract complex dependencies, for instance, to determine the set of servers that
simultaneously meet the requirements for throughput, latency, memory reserves, and historical
reliability. As a consequence, the branches of the decision tree in the optimization algorithm are
not explored exhaustively but are filtered according to semantic rules, which significantly reduces
computational complexity.</p>
      <p>Such an integration of semantic and mathematical layers makes it possible to construct
solutions that are not only optimal in terms of formal criteria but also contextually appropriate and
better aligned with the actual structure and behavior of the network. This enables a transition from
reactive load redistribution in the event of failures to proactive management, allowing critical
states to be predicted and the network configuration to be adapted based on continuously updated
knowledge. Ultimately, the ontological extension of the model forms the foundation for an
intelligent decision-support system that can explain its own conclusions, respond promptly to
failures, and adapt to real operating conditions of terminal networks in higher education
institutions.</p>
    </sec>
    <sec id="sec-6">
      <title>5. Implementation and Experimental Research</title>
      <p>The implementation of the proposed knowledge-oriented management system for terminal cluster
centers is based on a modular architecture that integrates the ontological layer, the optimization
core, the monitoring subsystem, and a web-based user interface (Fig. 4). This approach separates
concerns across components, supports scalability, simplifies maintenance, and enables future
extensions of the system without substantial modifications to the underlying codebase.</p>
      <p>On the server side, the core of the system is the ontology management module, which operates
on an OWL/RDF representation of the terminal cluster system model. The ontology is loaded into a
semantic repository that supports SPARQL querying and logical reasoning, thereby providing
access to up-to-date knowledge about terminal servers, user groups, operational states,
authentication policies, and historical monitoring events. A service layer built on top of the
ontology encapsulates the complexity of semantic operations and exposes a standardized
programmatic interface to the remaining components. The optimization subsystem that
implements dynamic load redistribution methods queries this service to obtain semantically filtered
candidate servers, reduced state spaces, and constraints derived from knowledge and rules. The
results of optimization — such as the optimal redistribution plan, the average service time, and the
efficiency ratio θ(n)/θα(n) — are returned to the service layer and may be written back into the
ontology as new facts or annotated decisions.</p>
      <p>In parallel, the monitoring subsystem collects real-time data on the state of terminal servers,
load levels, available memory resources, and failure events. These data are used both to update
optimization model parameters and to enrich the ontology with new individuals of classes such as
ServerState and MonitoringEvent. This enables the establishment of a feedback loop: monitoring
produces events, the ontology accumulates structured knowledge, the optimization core makes
decisions based on this knowledge, and the results of these decisions are fed back into the system
for continuous refinement.</p>
      <p>The user interface is implemented as a single-page web application with a modern adaptive
design tailored for security administrators and network operations engineers (Fig. 5). The main
view adopts a dashboard layout that aggregates key performance indicators, a detailed table of
server states, an event and semantic decision log, and a panel with ontology concepts and SPARQL
query examples. The page layout follows a two-column structure: a compact sidebar on the left
presents summarized cluster information, while the right side contains the primary working area
featuring server status tables and the chronological decision timeline.</p>
      <p>At the top of the page, a header contains the system’s branding, a concise textual description of
the dashboard's purpose, and status indicators. The user receives immediate visual feedback on the
activity of the monitoring subsystem and can initiate a redistribution process via an interactive
control. A theme switcher (light/dark mode) is provided, implemented through dynamic CSS
variable updates, to enhance usability under different lighting conditions.</p>
      <p>The sidebar includes an overview block displaying aggregated indicators: the number of
terminal servers, the number of currently active nodes, the current average authentication service
time , and the integrated efficiency metric ( )/ (), which quantifies the improvement obtained
by combining branch-and-bound optimization with ontological filtering. A compact list of core
ontology concepts is presented as a visual legend to support interpretation of the semantic layer.
Below, a SPARQL query fragment illustrates how the system selects candidate servers according to
trust values, available memory, and policy constraints.</p>
      <p>The main area contains a detailed table of terminal server states with information on cluster
membership, operational status (online, degraded, failed), load levels, trust ratings, and available
memory. Visual markers — such as colored badges and status pills—help administrators quickly
identify critical nodes and evaluate load distribution. Adjacent to the table is a chronological
decision log that records detected failures, results of semantic candidate selection, key steps in the
optimization workflow, and the final redistribution plan. Each entry provides a brief event
description and contextual explanation of which ontological elements or KnowledgeRule
constraints were involved in the corresponding decision.</p>
      <p>The page concludes with an explanatory section summarizing how the knowledge-oriented
decision was produced: from failure detection and semantic reasoning, through candidate filtering
and constraint enforcement, to the final optimization step operating on a reduced search space.
This section serves as an element of explainable analytics, essential for integrating
decision-support components into critical infrastructure.</p>
      <p>Overall, the system implementation integrates semantic technologies, optimization methods,
and a modern web interface to support the full operational cycle: monitoring → ontological
modeling → optimization computation → visualization and explanation of decisions. This
approach increases the resilience and efficiency of authentication channels in terminal cluster
centers of university networks while ensuring transparency, interpretability, and usability for
expert administrators.</p>
    </sec>
    <sec id="sec-7">
      <title>6. Conclusion</title>
      <p>This study develops a comprehensive knowledge-oriented approach aimed at enhancing the
resilience, efficiency, and intelligence of terminal cluster systems responsible for user
authentication in the corporate networks of higher education institutions. By integrating
mathematical modeling, semantic technologies, and advanced optimization methods, the research
presents a unified framework for the dynamic redistribution of load among terminal servers under
conditions of failures, peak loads, and limited communication bandwidth.</p>
      <p>One of the key outcomes of the study is the construction of a formal model of terminal cluster
centers represented as an open stochastic network. This model enables accurate estimation of flow
intensities, authentication service time, and the impact of server failures on the global performance
indicator 0. The research demonstrates that the problem of optimal redistribution of user groups
among operational servers belongs to the class of high-complexity combinatorial problems, while
exhaustive enumeration is impractical due to the exponential growth of candidate configurations.</p>
      <p>A central innovation of this work is the development of an ontology of terminal cluster systems,
which enables semantic representation of the network structure, server resources, access policies,
logical dependencies, historical states, and behavior patterns. The ontology formalizes relationships
among system components, ensures the logical consistency of knowledge, and enables automated
inference. Its integration with the mathematical model significantly improves the relevance and
correctness of redistribution decisions, since semantic restrictions automatically eliminate
infeasible, conflicting, or suboptimal variants before numerical optimization begins.</p>
      <p>The proposed algorithm, which combines a branch-and-bound method with semantic filtering
based on SPARQL queries and KnowledgeRule constraints, substantially reduces computational
complexity. Experimental results confirm that semantic technologies reduce the search space by
orders of magnitude, enabling rapid construction of optimal redistribution plans and achieving a
significant reduction of the average authentication service time 0. At the same time, the approach
ensures compliance with technical, policy, and contextual constraints—an outcome unattainable in
purely numerical models.</p>
      <p>A full-scale software system was implemented to validate the proposed approach. It includes an
OWL/RDF knowledge repository, a SPARQL query engine, an optimization core, a real-time server
monitoring subsystem, and a modern web interface. The developed dashboard provides intuitive
visualization of cluster parameters, server state tables, event and decision timelines, and semantic
explanations of the reasoning process. This architecture enables prompt reaction to failures,
enhances the transparency of system behavior, and increases administrator trust in automated
decision-making.</p>
      <p>The results of the study demonstrate that combining mathematical optimization with
ontologybased knowledge representation forms a solid foundation for the development of intelligent
management systems for university-scale network infrastructures. The proposed approach
improves the availability of critical services, minimizes authentication delays, reduces the impact of
failures on end users, and ensures adaptive behavior of network infrastructure under dynamic
conditions and increasing workload.</p>
      <p>Promising directions for future research include integrating predictive failure models based on
machine learning, extending the ontology to support multi-realm authentication architectures,
applying causal analysis methods to assess the impact of configuration changes, and incorporating
Explainable AI techniques to improve transparency and interpretability of system
recommendations. Collectively, these developments may lead to a new class of decision-support
systems for managing distributed infrastructures with high requirements for reliability and
security.</p>
    </sec>
    <sec id="sec-8">
      <title>Declaration on Generative AI</title>
      <p>
        During the preparation of this work, the authors used ChatGPT and Grammarly to check grammar
and spelling, paraphrase, and reword the text. These tools help identify and correct grammatical
errors, typos, and other writing mistakes, improving the clarity and professionalism of the text.
After using these tools, the authors reviewed and edited the content as needed and take full
responsibility for the publication’s content.
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resource content based on analysis of semantic components, in: Proceedings of the 9th
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IEEE, New York, NY, 2019, pp. 297–302, doi:10.1109/ACITT.2019.8779897.
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