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Наука та прогрес транспорту. Вюник Дншропетровського нацюнального унiверситету залiзничного транспорту, 2018, № 6 (78)
МОДЕЛЮВАННЯ ЗАДАЧ ТРАНСПОРТУ ТА ЕКОНОМ1КИ
UDC 004.7:004.032.26
V. M. PAKHOMOVA1*, I. D. TSYKALO2*
'*Dep. «Electronic Computing Machines», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (056) 373 15 89, e-mail viknikpakh@gmail.com, ORCID 0000-0002-0022-099X
2*Dep. «Electronic Computing Machines», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (056) 373 15 89, e-mail ihor.tsykalo@gmail.com, ORCID 0000-0002-1629-5873
OPTIMAL ROUTE DEFINITION IN THE NETWORK BASED ON THE MULTILAYER NEURAL MODEL
Purpose. The classic algorithms for finding the shortest path on the graph that underlie existing routing protocols, which are now used in computer networks, in conditions of constant change in network traffic cannot lead to the optimal solution in real time. In this regard, the purpose of the article is to develop a methodology for determining the optimal route in the unified computer network. Methodology. To determine the optimal route in the computer network, the program model «MLP 34-2-410-34» was developed in Python using the TensorFlow framework. It allows to perform the following steps: sample generation (random or balanced); creation of a neural network, the input of which is an array of bandwidth of the computer network channels; training and testing of the neural network in the appropriate samples. Findings. Neural network of 34-2-410-34 configuration with ReLU and Leaky-ReLU activation functions in a hidden layer and the linear activation function in the output layer learns from Adam algorithm. This algorithm is a combination of Adagrad, RMSprop algorithms and stochastic gradient descent with inertia. These functions learn the most quickly in all volumes of the train sample, less than others are subject to reevaluation, and reach the value of the error of 0.0024 on the control sample and in 86% determine the optimal path. Originality. We conducted the study of the neural network parameters based of the calculation of the harmonic mean with different activation functions (Linear, Sigmoid, Tanh, Softplus, ReLU, L-ReLU) on train samples of different volumes (140, 1400, 14000, 49000 examples) and with various neural network training algorithms (BGD, MB SGD, Adam, Adamax, Nadam). Practical value. The use of a neural model, the input of which is an array of channel bandwidth, will allow in real time to determine the optimal route in the computer network.
Keywords: computer network; optimal route; neural network; sampling; harmonic mean; activation function; optimization algorithm
Introduction
One of the main requirements for routing algorithms is their rapid matching to an optimal solution, dictated by the need for their protocol realization in real time in the conditions of continuous change in the characteristics of network traffic, topology and load of computer networks used in the rail transport. Classic algorithms for finding the
Creative Commons Attribution 4.0 International doi: 10.15802/stp2018/154443
shortest path on the graph used in modern routing protocols cannot do this. One of the approaches to solving routing problems in computer networks is the use of neural network technology [8, 15-16]. For example, in [12] it is shown that with the help of a neural network (NN) it is possible to find a solution, close to the optimal, to the travelling salesman problem and to find the shortest path on the graph. In [3] for solving routing problems there
Наука та прогрес транспорту. Вюник Дншропетровського нацюнального унiверситету залiзничного транспорту, 2018, № 6 (78)
is studied the possibility of applying the following neural networks: Multi Layer Perceptron; RBF network; Hopfield network. It is established that the most promising means for solving the routing problem are the direct distribution neural network and the Hopfield network, which are capable of operating under conditions of dynamic change in the topology of the computer network and the characteristics of the data transmission channels [1-2]. In particular, when using the Hopfield network, additional research is required on the transfer functions of the neurons and on the energy of the neural network [18]. In [7], it was discovered that the Hopfield network finds a satisfactory route that differs from the optimal one by 7-8% in average (in the case of more than 15 seats). The possibility of using the Hopfield network to find the shortest path on the route graph in the computer network of railway transport is analysed [5-6]. In [3], the use of the direct distribution neural network created in MatLAB for the purpose of determining the route in a computer network of five nodes was investigated. But the integrated computer network of rail transport consists of a much larger number of nodes, which requires additional research. In particular, [20] proposed an intellectual control subsystem with the use of network technology, [17] - a subsystem of prediction based on a neural fuzzy network.
Purpose
To develop a methodology for determining the optimal route in the unified computer network based on the created software model «MLP34-2-410-34» using the TensorFlow framework.
Methodology
A combined computer network that works on different technologies can be represented as an unoriented graph G (V, W), where V is the set of
graph vertices, the number of which is N, with each vertex modelling a node (router) of the computer network; W is the set of graph edges, the number of which is M. Each graph edge is assigned with a certain weight corresponding to the bandwidth (the maximum amount of data transmitted by the network per unit time):
с=Ы ■
(i)
where
- bandwidth of the communication
channel between the z-th and j-th network nodes, Mbps.
To solve the routing problem, it is necessary to find the optimal path between the two routers assigned to the unified computer network. As an example, we will consider a hypothetical computer network whose structure is shown in Fig. 1 Let us introduce the array:
X=K} ,
(2)
where
- availability of traffic transmitted
within the network between the z-th and j-th vertices. As a limit Xj e{0.l}, i.e. the variable
takes value 1, if the traffic flows through the channel (z, j); otherwise - 0.
As the criterion of optimality, the following expression is supported:
min F • X,
X
(3)
where f =
125000000
which guarantees the
search for a path with the maximum bandwidth.
If there is no connection between the nodes of the unified computer network, then czj = cjz = 0 (hence, f =<»).
С
v
x
y
c
ij
Наука та прогрес транспорту. Вюник Дншропетровського нацюнального ушверситету з^зничного транспорту, 2018, N° 6 (78)
Fig. 1. Graph of router connections of unified computer network
Findings
Neural network as the main mathematical tool for solving the problem. In the unified computer network there are 30 routers and 34 communication channels. As an example, let us consider the solution to the problem of determining the optimal route between the nodes «12» and «1». Generally between the indicated nodes there are 14 unique paths.
Path 1: [12, 11, 13, 14, 15, 20, 21, 23, 1]; path 2: [12, 11, 10, 9, 8, 7, 6, 19, 2, 1]; path 3: [12, 11, 10, 9, 8, 7, 6, 5, 2, 1]; path 4: [12, 11, 10, 9, 8, 7, 6, 5, 3, 2, 1]; path 5: [12, 11, 13, 14, 15, 16, 17, 18, 19, 2, 1];
path 11: [12, 11, 10, 9, 8, 7, 6, 5, 2, 19, 18, 17, 16,
15, 20, 21, 23, 1];
path 12: [12, 11, 10, 9, 8, 7, 6, 5, 3, 2, 19, 18, 17,
16, 15, 20, 21, 23, 1];
path 13: [12, 11, 10, 9, 8, 7, 6, 5, 2, 19, 18, 17, 16,
15, 20, 21, 22, 24, 26, 1];
path 14: [12, 11, 10, 9, 8, 7, 6, 5, 3, 2, 19, 18, 17,
16, 15, 20, 21, 22, 24, 26, 1].
To solve the routing problem, we used the NN, whose structure is shown in Fig. 2. To the NN input, there is applied a vector of bandwidth of the channels of the unified computer network X, which characterizes its current state X = {xi}, where i = 1, ..., m (m = 34). For example, for NN, when
using the train sample of 1,400 examples, the path 6: [12, 11, 13, 14, 15, 20, 21, 22, 24, 26, 1]; number of required neurons in the hidden layer is path 7: [12, 11, 13, 14, 15, 16, 17, 18, 19, 6, 5, 2, estimated as follows:
1];
path 8: [12, 11, 13, 14, 15, 16, 17, 18, 19, 6, 5, 3, 2, 1];
path 9: [12, 11, 10, 9, 8, 7, 6, 19, 18, 17, 16, 15, 20, 21, 23, 1];
path 10: [12, 11, 10, 9, 8, 7, 6, 19, 18, 17, 16, 15, 20, 21, 22, 24, 26, 1];
34-1400
(1 + log21400) - (34 + 34)
-<L <
<
34. (1400 +1). (34 + 34 +1) + 34
34
34 + 34
Hence, 62 < L < 1456.
Наука та прогрес транспорту. Вюник Дншропетровського нацюнального унiверситету залiзничного транспорту, 2018, № 6 (78)
Fig. 2. Structure of multilayer NN
Sample preparation (preparatory stage). Formation of the sample is carried out according to the fixed structure of the unified computer network (see Fig. 1). The input vector X is constructed by randomly generating channel bandwidth values Cjj, while these values are formed by a uniform
distribution onto the segments [100; 100,000,000]. The response vector Y is generated by calculating the optimal path according to the Dijkstra algorithm using the Python language of the Networkx library (open source software library used to work with graphs and networks).
The samples are constructed so that each of 14 unique paths is present at the same frequency. The test sample has 700 examples, validation sample has 700 examples, the first train sample has 140 examples (10 examples for each path), the second train sample has 1,400 examples (100 examples for each path), the third training sample - 14,000 examples (1,000 examples for each path), the fourth train sample - 49,000 examples (3,500 examples for each path).
All data is initially normalized to the range from 0 to 1 by the formula:
x = -
x - min(X ) max(X ) - min(X )
x e X
(4)
The structure of the resulting vector is as follows: Y = [y 1,2, y1,26, y 1,29, y1,23, y2,19, y2,3, y2,5, y2,4,
y3,5, y5,6, y6,19, y6,7, y7,8, y8,9, y9,10, y10,11, y11,12, y11,13, y13,14, y14,15, y15,16, y15,20, y16,17, y17,18, y18,19, y20,21,
y21,22, y21,23, y22,24, y24,25, y24,26, y26,27, y27,28, y29,30],
where ytJ e {0.1}, that corresponds to using or not
using the appropriate channel in the route.
Justifying the choice of modelling tools. To solve the routing problem in the unified computer network, the Keras library was selected using Ten-sorFlow and Numpy in the Python programming language [9-11, 13-14, 19].
Keras is an open neural network library in Python language capable of working on top of Deeplearning4, TensorFlow and Theano, designed for quick neural network deep learning experiments.
TensorFlow is an open source software library for machine learning. It is the second-generation GoogleBrain machine learning system released as open source software.
Numpy is an extension of the Python language that supports large, multidimensional arrays and matrices, along with a library of high-level mathematical functions for operations with these arrays.
Python is an interpreted object-oriented highlevel programming language with strict dynamic typing. High-level data structures, along with dynamic semantics and dynamic linking, make it attractive for rapid development of applications, as well as a tool for existing components. Python supports modules and module packages, which facilitates modularity and reuse of the code. Python interpreter and standard libraries are available both in compilation and in source form on all major platforms. Python programming language supports several programming paradigms, including: object-oriented; procedural; functional; aspect-oriented.
Structure of MLP 34-2-410-34 software model. MLP 34-2-40-34 software model, created for modelling and research, consists of the main module «Main» and the following classes: Generator, MLPModel, NetworkX, Matplotlib, Keras.Model, Metrics, Tensorflow. The main module «Main» provides the menu tasks: 1 - sample generation; 2 - neural network training; 3 - neural network testing. «Generator» performs a sample preparation in two modes: random (calculating the random number of examples for each path, Fig. 3, a); balanced (the same number of examples for each possible path, Fig. 3, b). For example, a sample of 140 examples in balanced mode takes 5 minutes, while in random mode it takes less than one minute.
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Fig. 3. Generation of sample:
a -random; b -balanced
«MLPModel» creates a neural network of 34-2-X-34 configuration (where X is the possible number of hidden neurons) and performs the following steps: training; testing; control on the corresponding samples and their normalization.
«NetworkX» (standard class) builds a graph of the computer network (Graph), calculates the existing paths between stations (all_simple_paths), the path between the specified stations according to the Dijkstra algorithm (bidirectional_dijkstra).
«Matplotlib» (standard class) builds a pie chart and histogram to show the ratio of the number of examples for each path.
«Keras.Model» (standard class) performs compilation in accordance with the given configuration of the neural network (compile), represents the standard functions (fit, predict) that are used during the training and testing of the neural network.
«Metrics» performs the calculation of the pro-
bability of the optimal and of correct answers.
«TensorFlow» (standard class) is called by the «Keras.Model» class when performing the appropriate calculations.
The overall structure of MLP 34-2-40-34 software model is shown in Fig. 4
In order to be able to unambiguously compare the NN models in two parameters - the probability of optimal responses and the probability of correct responses, we entered the value of the harmonic mean, which is calculated by the following formula:
H =
2popt pcor popt + pcor
(5)
where pop - probability of optimal responses, pcor - probability of correct responses.
b
a
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Fig. 4. Structure of MLP 34-2-40-34 software model
ing feature vector of channel entry to the optimal path is as follows: {0,0,0,1,0,0,0,
0,0,0,0,0,0,0,0,0,1,1,1,1,0,1,0,0,0,1,0,1,0,0,0,0,0,0},
routers in the network:1-23, 11-12, 11-13, 13-14,
14-15, 15-20, 20-21, 21-23 . The resulting path is
shown in Fig. 5
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Fig. 5. The resulting optimal path consisting of channels:
12-11, 11-13, 13-14, 14-15, 15-20, 20-21, 21-23, 23-1
Study of the NN training effectiveness for different number of neurons in the hidden layer. The study on the NN model was performed using the stochastic gradient descent algorithm (batch size 64) with Adam optimization (training speed a = 0.001, inertia ft = 0.9, RMSprop ß2 = 0.999,
decay = 10r5) on 1,400 study examples, over 1,000
epochs for different numbers of hidden neurons: L = {62,410,760,1110,1456}.
The results of the experiment are shown in the Table 1. From the table it is clear that for the train sample the best result of 0.99 is already achieved with 410 neurons in the hidden layer.
Table 1
Study of NN for different number of hidden neurons
Number of hidden neurons 62 410 760 1 110 1 456
popt 0.77 0.99 0.99 0.99 0.99
Train sample pcor 0.81 0.99 0.99 0.99 0.992
H 0.79 0.99 0.99 0.99 0.99
popt 0.55 0.52 0.51 0.52 0.51
Test sample pcor 0.71 0.7 0.69 0.7 0.71
H 0.62 0.6 0.59 0.6 0.59
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The NN training process is illustrated in the objective function-epoch dependency graphs for the train and test samples in Fig. 6-10.
Fig. 6. The 34-2-64-34 NN error-epoch dependency graph on samples:
a - train; b - test
Fig. 6. The 34-2-410-34 NN error-epoch dependency graph on samples:
a - train; b - test
b
0.0600 0.0200
300.0
600.0
900.0
0.000
300.0
600.0
Fig. 6. The 34-2-760-34 NN error-epoch dependency graph on samples:
a - train; b - test
b
a
b
а
а
а
0.250 0.200 0.150 0.100 0.0500 0.00
а
0.250 0.200 0.150 0.100 0.0500 0.00
Figures 6-10 show that all of the proposed NN models feature re-training after the 200th epoch. Since the NN model of 34-2-410-34 configuration gives the best result for a relatively small number of neurons, it is selected for further research as the most promising one.
Study of the NN training effectiveness for various activation functions and train sample sizes. The efficiency of the 34-2-410-34 NN model is studied for various neuron activation functions in the hidden layer. The output layer has a linear activation function. The training was carried out using
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b
the stochastic gradient descent algorithm (batch size 64) with Adam optimization (learning speed a = 0.001, inertia ft = 0.9, RMSprop p2 = 0.999,
decay = 10"5) for 1,000 epochs. Experiments were performed for various activation functions in the hidden layer (linear, sigmoid, hyperbolic tangent, Softplus, ReLU, Leaky-ReLU a = 0.1; Table 2) and for different train sample sizes (140, 1,400, 14,000 and 49,000 examples). The results of NN modelling are given in Table 2-4, the NN training process is illustrated in Fig. 11-14.
Г
1
4 —»
S a 1
o.ooo 300.0 600.0 900.0
Fig. 6. The 34-2-1110-34 NN error-epoch dependency graph on samples:
a - train; b - test
b
0.220 0.180 0.140 0.100 0.0600 0.0200 -0.0200
0.000 300.0 600.0 900.0
Fig. 6. The 34-2-1456-34 NN error-epoch dependency graph on samples:
a - train; b - test
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Fig. 11. The MSE error-epoch dependency graph for train and test samples of 140 examples:
The study showed that NN training for Softplus further training. In addition, one can see the attri-and Sigmoid activation functions did not stop, and butes of the NN re-training for Tanh and Softplus it is possible to achieve greater accuracy during activation functions.
Table 2
Study of NN for various activation functions on train sample of 140 examples
Activation function Linear Sigmoid Tanh Softplus ReLU L-ReLU
popt 0.28 0.58 1 0.78 1 1
Train sample pcor 0.32 0.61 1 0.78 1 1
H 0.3 0.6 1 0.78 1 1
popt 0.07 0.17 0.03 0.1 0.16 0.16
Test sample pcor 0.11 0.29 0.05 0.18 0.25 0.28
H 0.09 0.21 0.04 0.13 0.19 0.2
The table shows that on the small volumes of in training data was shown by the activation func-
data the activation functions Sigmoid, ReLU and Leaky-ReLU showed themselves the most successfully on the test sample. The best result of accuracy
tions Tanh, ReLU, Leaky-ReLU, so they can be considered promising for larger sample sizes.
Fig. 12. The MSE error-epoch dependency graph for train and test samples of 1,400 examples.
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Table 3
Study of NN for various activation functions on train sample of 1,400 examples
Activation function Linear Sigmoid Tanh Softplus ReLU L-ReLU
popt 0.2 0.98 1 0.99 1 1
Train sample Pcor 0.24 0.99 1 0.99 1 1
H 0.22 0.98 1 0.99 1 1
popt 0.19 0.53 0.06 0.3 0.46 0.46
Test sample pcor 0.24 0.7 0.06 0.35 0.61 0.61
H 0.21 0.6 0.6 0.32 0.53 0.52
. j . test sample. Except for the linear activation func-
The table shows that on the average data
jT-ir>TTT jt i r>TTT tion, all functions have given maximum accuracy volumes, Sigmoid, Tanh, ReLU and Leaky-ReLU . . , ^ ° J
.. .. p j.* .c i ..I on the training data.
activation functions were most successful on the °
Table 4
Study of NN for various activation functions on train sample of 14,000 examples
Activation function Linear Sigmoid Tanh Softplus ReLU L-ReLU
popt 0.2 1 0.99 0.99 1 1
Train sample pcor 0.24 1 0.99 0.99 1 1
H 0.22 1 0.99 0.99 1 1
popt 0.19 0.66 0.57 0.61 0.76 0.74
Test sample cor p 0.24 0.78 0.63 0.67 0.86 0.83
H 0.21 0.71 0.6 0.64 0.81 0.79
The table shows that on the data volumes big- the test sample. Except for the linear activation ger than the average, Sigmoid, ReLU and Leaky- function, all functions have given maximum accu-ReLU activation functions were most successful on racy on the training data.
Fig. 13. The MSE error-epoch dependency graph for train and test samples of 1 14,000 examples
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Table 5
Study of NN for various activation functions on train sample of 49,000 examples
Activation function Linear Sigmoid Tanh Softplus ReLU L-ReLU
popt 0.2 1 0.96 1 1 1
Train sample Pcor 0.24 1 0.96 1 1 1
H 0.22 1 0.96 1 1 1
popt 0.19 0.81 0.8 0.76 0.83 0.85
Test sample pcor 0.24 0.86 0.84 0.8 0.9 0.9
H 0.21 0.83 0.82 0.78 0.86 0.88
Fig. 14. The MSE error-epoch dependency graph for train and test samples of 49,000 examples
The resulting NN of 34-2-410-34 configuration with the activation function Leaky-ReLU (a = 0.1) in the hidden layer and the linear activation fUnction in the output layer after training with 49,000 examples for 1,000 epochs reached MSE value of 0.0024 on the control sample and in 86% determines the optimal path.
Originality and practical value
The NN of 34-2-410-34 configuration with activation function Leaky-ReLU (a = 0.1) in the hidden layer and with linear function in the output
layer was studied. Experiments were conducted for various training optimization algorithms during 100 epochs for the sample size of 49,000 examples. The results of experiments are shown in the table 6, the training process is illustrated in Fig. 15.
According to the results of experiments, it is evident that the NN in the classical gradient descent learns very slowly; the NN in the stochastic gradient descent shows a significant improvement. Adam, AdaMax and Nadam training algorithms showed almost identical results.
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Study of NN of 34-2-410-34 configuration by different algorithms
Table 6
Algorithm BGD MB SGD Adam Adamax Nadam
popt 0 0.09 0.99 0.96 0.99
Train sample pcor 0 0.1 1 0.97 0.99
H 0 0.1 0.99 0.96 0.99
popt 0 0.11 0.87 0.85 0.87
Test sample pcor 0 0.12 0.92 0.9 0.92
H 0 0.11 0.89 0.87 0.9
Fig. 15. The MSE error-epoch dependency graph for train and test samples for different training algorithms
Conclusions
1. The routing problem in the unified computer network is solved based on the developed software model «MLP 34-2-410-34» using the Python language and the TensorfFow framework, which allows generating the samples: train (140, 1 400, 14,000, 49,000 examples); test (700 examples); control (700 examples), as well as modelling the work of the neural network and studying its parameters.
2. Efficiency was studied based on the harmonic mean of the NN of 34-2-X-34 configuration with sigmoid activation function in the hidden layer and linear function in the output layer for different number of hidden neurons: 62; 410; 760; 1 110; 1 456. During NN training we used the
modern Adam algorithm for optimizing stochastic gradient descent with recommended hyperparameters: learning speed a = 0.001; inertia 0.9;
RMSprop p2 = 0.999; decay = 10"5. The study showed that the accuracy of the neural network can be reached with 410 hidden neurons, and the further increase does almost nothing to improve the results.
3. Efficiency was studied based on the harmonic mean of the NN of 34-2-410-34 configuration under different activation functions: linear; sigmoid hyperbolic tangen-som; Softplus, ReLU; Leaky-ReLU using the Adam algorithm on train samples of different size (140, 1 400, 14,000, 49 000 examples). The study has shown that the activation functions ReLU and Leaky-ReLU train the most rapidly at all levels of the train sample and
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less than other activation functions are subject to re-training. The NN of 34-2-410-34 configuration for activation functions Tanh and Softplus can achieve 100% accuracy on the train sample, but these functions are less slowly learned than ReLU and Leaky-ReLU and are strongly subject to retraining with insignificant sizes of the train sample (140, 1,400 and 14,000 examples). When using the sigmoid activation function, the neural network is also retrained, but with a large size of train examples (49,000 examples) it is able to achieve accura-
cy (83%) close to Leaky-ReLU (88%) or ReLU (86%).
4. Efficiency of the NN of 34-2-410-34 configuration was studied with activation function Leaky-ReLU (a = 0.1) in the hidden layer and with linear function in the output layer. Experiments were conducted by different optimization algorithms (BGD, MB SGD, Adam, Adamax, Nadam) during 100 epochs with the train sample of 49,000 examples. Adam, Adamax, and Nadam algorithms showed almost identical results, with 89, 87, and 90% accuracy, respectively.
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Наука та прогрес транспорту. Вюник Дншропетровського нацюнального унiверситету залiзничного транспорту, 2018, N° 6 (78)
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В. М. ПАХОМОВА1*, I. Д. ЦИКАЛО2*
'*Каф. «Електронш обчислювальш машини», Дшпропетровський нацюнальний ушверситет залiзиичиого транспорту iменi академжа В. Лазаряна, вул. Лазаряна, 2, Дншро, Украша, 49010, тел. +38 (056) 373 15 89, ел. пошта viknikpakh@gmail.com, ORCID 0000-0002-0022-099X
2*Каф. «Електронш обчислювальш машини», Дншропетровський нацюнальний ушверситет затзничного транспорту iменi академжа В. Лазаряна, вул. Лазаряна, 2, Дншро, Украша, 49010, тел. +38 (056) 373 15 89, ел. пошта ihor.tsykalo@gmail.com, ORCID 0000-0002-1629-5873
ВИЗНАЧЕННЯ ОПТИМАЛЬНОГО МАРШРУТУ В КОМП'ЮТЕРНШ МЕРЕЖ ЗАСОБАМИ БАГАТОШАРОВО1 НЕЙРОННО1 МОДЕЛ1
Мета. Класичт алгоритми пошуку найкоротшого шляху на граф!, що лежать в основi наявних протоко-лiв маршрутизаци, якi сьогоднi використовують у комп'ютерних мережах, в умовах постшно! змiни заван-таженостi мережi не можуть привести до оптимального ршення в реальному часi. У зв'язку з цим метою статп е розробити методику визначення оптимального маршруту в об'еднанш комп'ютернiй мережа Методика. Для визначення оптимального маршруту в об'еднанш комп'ютернш мереж!, що працюе за ргзними техноло-пями, розроблено на мов! Python використанням фреймворку TensorFlow програмну модель «MLP 34-2-410-34». Вона дозволяе виконувати наступт етапи: генерацш виб!рки (випадкову або збалансо-вану); створення нейронно! мереж!, на вхвд яко! подають масив пропускних спроможностей канал!в комп'ютерно! мереж!; навчання й тестування нейронно! мереж! на ввдповщних виб!рках. Результати. Ней-ронна мережа конфпурацп 34-2-410-34 з функщями активаци ReLU та Leaky-ReLU у прихованому шар! та лшшною функшею активаци у вихвдному шар! навчаеться за алгоритмом Adam. Цей алгоритм е комбшаць ею алгоршшв Adagrad, RMSprop та стохастичного град!ентного спуску з шершею. Зазначеш функци нав-чаються найбшьш швидко на вах обсягах навчально! виб!рки, менш за шш! тддаються перенавчанню, й досягають значения помилки в 0,0024 на контрольнш виб!рш й у 86 % визначае оптимальний шлях. Наукова новизна. Проведено дослщження параметр!в нейронно! мереж! на основ! розрахунку середнього гармоншного за р!зних функцш активаци (Linear, Sigmoid, Tanh, Softplus, ReLU, L-ReLU) на навчальних виб!рках р!зного обсягу (140, 1 400, 14 000, 49 000 приклащв) та за р!зними алгоритмами ошгашзацп навчання нейронно! мереж! (BGD, MB SGD, Adam, Adamax, Nadam). Практична значимкть. Використання нейронно! модел!, на вхщ яко! подають значення пропускних спроможностей канал!в, дозволить у реальному час! визначити оптимальний маршрут в об'еднанш комп'ютернш мереж!.
Ключовi слова: комп'ютерна мережа; оптимальний маршрут; нейронна мережа; виб!рка; середне гармо-ншне; функшя активаци; алгоритм ошгашзаци
Наука та прогрес транспорту. Вюник Дншропетровського нащонального унiверситету залiзничного транспорту, 2018, № 6 (78)
В. Н. ПАХОМОВА1*, И. Д. ЦЫКАЛО2*
'*Каф. «Электронные вычислительные машины», Днепропетровский национальный университет железнодорожного транспорта имени академика В. Лазаряна, ул. Лазаряна, 2, Днипро, Украина, 49010, тел. +38 (056) 373 15 89, эл. почта viknikpakh@gmail.com, ORCID 0000-0002-0022-099X
2*Каф. «Электронные вычислительные машины», Днепропетровский национальный университет железнодорожного транспорта имени академика В. Лазаряна, ул. Лазаряна, 2, Днипро, Украина, 49010, тел. +38 (056) 373 15 89, эл. почта ihor.tsykalo@gmail.com, ORCID 0000-0002-1629-5873
ОПРЕДЕЛЕНИЕ ОПТИМАЛЬНОГО МАРШРУТА В КОМПЬЮТЕРНОЙ СЕТИ СРЕДСТВАМИ МНОГОСЛОЙНОЙ НЕЙРОННОЙ МОДЕЛИ
Цель. Классические алгоритмы поиска кратчайшего пути на графе, что лежат в основе существующих протоколов маршрутизации, которые сегодня используют в компьютерных сетях, в условиях постоянного изменения загруженности сети не могут привести к оптимальному решению в реальном времени. В связи с этим целью статьи является разработать методику определения оптимального маршрута в объединенной компьютерной сети. Методика. Для определения оптимального маршрута в объединенной компьютерной сети, которая работает по разным технологиям, написана на языке Python с использованием фреймворка TensorFlow программная модель «MLP 34-2-410-34». Она позволяет выполнять следующие этапы: генерацию выборки (случайную или сбалансированную); создание нейронной сети, на вход которой подают массив пропускных способностей каналов компьютерной сети; обучение и тестирование нейронной сети на соответствующих выборках. Результаты. Нейронная сеть конфигурации 34-2-410-34 с функциями активации ReLU и Leaky-ReLU в скрытом слое и линейной функцией активации в результирующем слое обучается по алгоритму Adam. Этот алгоритм является комбинацией алгоритмов Adagrad, RMSprop и стохастического градиентного спуска с инерцией. Указанные функции учатся наиболее быстро на всех объемах учебной выборки, меньше других поддаются переобучению, и достигают значения ошибки в 0,0024 на контрольной выборке и в 86 % определяют оптимальный путь. Научная новизна. Проведено исследование параметров нейронной сети на основе расчета среднего гармоничного при разных функциях активации (Linear, Sigmoid, Tanh, Softplus, ReLU, L-ReLU) на учебных выборках разного объема (140, 1 400, 14 000, 49 000 примеров) и за различными алгоритмами оптимизации обучения нейронной сети (BGD, MB SGD, Adam, Adamax, Nadam). Практическая значимость. Использование нейронной модели, на вход которой подают значения пропускных способностей каналов, позволит в реальном масштабе времени определить оптимальный маршрут в объединенной компьютерной сети.
Ключевые слова: компьютерная сеть; оптимальный маршрут; нейронная сеть; выборка; среднее гармоничное; функция активации; алгоритм оптимизации
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Received: July 27, 2018 Accepted: Nov. 06, 2018
