## 2 Methodologies  
The development of a secure IP network based on Asterisk PBX involves implementing several security measures, including network design, access control, encryption, firewall configuration, network monitoring, regular updates and patching, and user education. These measures can help ensure the security, confidentiality, and availability of data transmitted over the network.  
The development of a secure IP network based on Asterisk PBX consists of several steps:  
Step 1. We need to install and configure the Asterisk PBX software on servers in two cities. In our case, one server is located in Germany, the other in the Netherlands.  
The IP telephony network consists of two servers on which the Asterisk software is installed, as shows in Figure 1.  
To install the Asterisk software, it was decided to use hosting, and servers in Germany and the Netherlands were selected.  
Thus, building a network based on Asterisk Private Branch Exchange based on Internet Protocol (IP PBX) starts with analyzing and choosing a Linux distribution. The Ubuntu operating system was chosen, which offers a well-designed platform for IP-PBX and is reliable.  
Step 2. We need to configure the IP phones that connect to the PBX. In our case, dial plan is configured on the servers. Blink is installed as a softphone. It is available for free and easy to use.  
Step 3. After setting up the PBX and devices, we should test the network to make sure that it works properly and that all devices can connect and make/receive calls.  
Step 4. After setting up the network, we need to analyze its security. This includes identifying potential vulnerabilities with Wireshark.  
Step 5. To mitigate the impact of vulnerabilities on the network, we use the TLS protocol setting. TLS provides a secure communication channel between two endpoints by encrypting the data exchanged between them. When two endpoints establish a TLS connection, they negotiate a set of cryptographic protocols, algorithms, and parameters to use for the encryption and decryption of data. This negotiation is achieved through a process called the TLS Handshake Protocol, which ensures that both endpoints agree on the same set of parameters and that the parameters are not vulnerable to known attacks.  
The TLS Handshake Protocol involves the following steps:  
Client hello: The client sends a message to the server indicating its preferred encryption algorithms and other parameters.  
Server hello: The server responds with a message indicating the encryption algorithms and other parameters that will be used for the connection.  
Certificate exchange: The server sends its digital certificate to the client to prove its identity.  
Key exchange: The client and server exchange encryption keys, which are used to encrypt and decrypt data exchanged between them.  
Authentication: The client and server authenticate each other using the digital certificates exchanged earlier.  
Session key generation: The client and server use the exchanged encryption keys to generate a unique session key, which is used for the remainder of the connection.  
Encryption: The client and server use the session key to encrypt and decrypt data exchanged between them. This provides a high level of security for communication over the internet, even if the underlying network is untrusted or compromised.  
The process of exchanging such messages is shown in Figure 2.  
Overall, the TLS protocol provides a high level of security for communication over the internet, and its use has become increasingly important as the volume and sensitivity of online communication continues to grow.  
Figure 1: The developed network based on Asterisk IP PBX.