13. Basic issues of VoIP communication

Key definitions

VoIP - https://pl.wikipedia.org/wiki/Voice_over_Internet_Protocol
PBX - https://pl.wikipedia.org/wiki/PBX
Codec - https://pl.wikipedia.org/wiki/Kodek
SIP - https://pl.wikipedia.org/wiki/Session_Initiation_Protocol


What is VoIP? 

VoIP is an acronym for Voice over Internet Protocol. It is a technology that allows audio to be sent and received over a computer network, this technology is used to make 'phone calls' in real time. 
Although VoIP technology has become very popular over the past decade the history of VoIP begins nearly 100 years ago at the Bell Labs research institute. 


In 1938, Homer Dudley, a Bell Labs engineer, created the first electronic speech synthesiser, known as the Vocoder.  The concept of operation was similar to today's packet transmission (IP), which records voice samples on one phone and plays them back on another. Today, the same technology is used not only in VoIP telephony, but also in cochlear implants.  


It is not possible to make calls over the Internet without a computer network. The history of computer networking begins in 1969 at the Advanced Research Project Agency - a US government agency. The agency's work led to the development of the TCP/IP network protocol and the launch of the first computer network, ARPANET. This network continued to operate formally until 1990.  
In 1973, at MIT, Bob McAuley, Ed Hofstetter and Charlie Radar developed the first voice packet transmitted over ARPANET. 

This voice transmission was made possible by LPC, or Linear Predictive Coding - the foundation of modern VoIP technology. LPC is a speech analysis technique that relies on a linear predictive model to process and re-synthesise compressed digital forms of voice and speech signals. 

At the time, ARPANETs could not be used privately. The first 'technical' cybercriminal was Leonard Kleinrock, who in 1973 sent a message over ARPANET regarding his missing electric razor. 

In 1974, Lincoln Lab and Culler Harrison Inc. successfully transmitted test voice data packets between them. In 1976, Culler Harrison and Lincoln Labs conducted a teleconference via LPC. In 1982 they made significant progress, using the LPC to connect over the local cable network, mobile packet network and interface with the PSTN (Public Switched Telephone Network). 

In 1988, the ITU-T approved the G.722 wideband audio codec, a programme that allows audio to be converted into 'digital' language and, once transmitted over the network, converted back into an audio signal. The G.722 codec offered significantly improved speech quality compared to its predecessors. G.722 offers data rates of up to 64 kbps, making it ideal for VoIP communication - especially in local area networks (LANs). 

In 1989, developer Brian C. Wiles created RASCAL, the first system that successfully transmitted voice over Ethernet networks - the first VoIP application. 

In 1991, John Walker of Autodesk wrote and released NetFone, later known as Speak Freely, the first software-based VoIP phone.  

1993 brought the first video conferencing system, Teleport. The developers of Teleport were David Allen and Herold Williams, who sold their product to Hilton Hotels. 

The first commercial VoIP application became the VocalTec Internet Phone programme in 1995. The programme used the H.323 protocol, the requirements were a 486 processor, 8 MB of RAM, a 16-bit sound card and an SLLP or PPP internet connection.  VocalTec was cheaper than traditional telephone calls for international and long-distance calls. 

In 1996, SIP (Session Initiation Protocol) was developed. The first version of SIP had only one command - 'make a call' - but by 1999 the capabilities of SIP had been expanded to six commands. VocalTec Internet Phone programme. The programme used the H.323 protocol, the requirements were a 486 processor, 8 MB of RAM, a 16-bit sound card and an SLLP or PPP internet connection.  VocalTec was cheaper than traditional telephone calls for international and long-distance calls. 

In 1996, SIP (Session Initiation Protocol) was developed. The first version of SIP had only one command - 'make a call' - but by 1999 the capabilities of SIP had been expanded to six commands. 

 Pole tekstowe 

SIP has become the preferred protocol for mobile VoIP telephony. 

 In 1999, Mark Spencer decided to program his own IP-PBX system, a program that acts as a telephone exchange, and call it Asterisk. Asterisk is an open source program that quickly gained popularity and is still being developed and improved today by thousands of developers.  

In 2003, Skype was created and soon became the most widely used voice communicator. Over time, Skype developed into a video instant messenger with file transfer capabilities. Today, it is owned by Microsoft. 

In 2006, Truphone, the first mobile VoIP application, was launched for Nokia, iPhone, Android and Blackberry users.  The app uses SIP to make calls over an internet connection rather than over mobile networks.  

Between 2011 and 2015, the US saw a great increase in the popularity of VoIP telephony. Globally, there has been an increase in the number of VoIP providers, which has fostered competition and is leading or has already led to the displacement of legacy phone systems. 

The COVID pandemic of 2020 has changed the nature of work to remote working overnight in many sectors of the economy. Unified communications based on VoIP technology allows teams to work remotely and contact customers through multiple channels, including: video calls, mobile apps, conference calls, team text messaging, voicemail. 

Some of the most popular software applications that use VoIP technology include: Microsoft Teams (the default messenger for the MS Windiows11 operating system), Google Meet, Zoom. 

VoIP at home, VoIP for business

VoIP solutions for home users 

Home users are those who generally require a single telephone number.  

In order to set up a public PSTN phone number with a state and area (city) prefix, you need to register with a VoIP service provider. The VoIP provider will, in the registration process, create a SIP account - a login and password, and tell you how to configure SIP. Having the account information, we can log in to the PBX and use VoIP telephony in applications for mobile phones, applications installed in Microsoft, Apple, Linux operating systems, or finally VoIP phones. 

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VoIP solutions for companies 

In order to manage multiple VoIP telephones in a company, it is necessary to set up a PBX. The PBX can be either a physical device installed in the company's premises or a virtual PBX (software provided by the company selling telephony services). 

In the case of a virtual PBX, the fixed telephones of the company's employees must support VoIP. The cost of a VoIP phone is comparable to a traditional phone, so for new company premises, a VoIP phone seems to be the best choice.  

Companies with traditional PSTN lines and handsets can stay with the allocated telephone numbers in two ways: 

  • purchasing a VoIP PBX with PSTN/ISDN modules without replacing phones, 
  • transferring the numbers to a virtual PBX and replacing the telephones with VoIP-enabled ones. 


Overview of VoIP applications 

VoIP-related applications can be divided into:  

  • client - installed on VoIP end user's telephones/computers 
  • server applications - installed on regular servers or dedicated PBXs. 


Client applications 

Modern mobile phone technology is based on digital technology, so audio is transmitted via a codec.  

On current smartphones, adding a VoIP number is possible without installing additional software. In the Android or iOS settings, we can enter our SIP account details and use VoIP telephony. There are also many VoIP apps that give additional functionality (e.g. shared address book, etc.). When choosing how we want to use VoIP telephony, it is best to follow the recommendations of the VoIP service provider. Service providers often have their own application dedicated to the use of VoIP services. 

On desktop computers, laptops or tablets without the possibility of connecting to a mobile network, we can use VoIP via the Internet. So all you need to do is connect your laptop to WiFi and install a VoIP application to make phone calls.  

There are many popular applications that allow VoIP telephony connections to the public switched telephone network (PSTN) :  Microsoft Teams, ZOIPER, Blink, Zoom, etc. We can follow the list of VoIP client applications at: https://en.wikipedia.org/wiki/List_of_SIP_software  ;


Server applications 

The SIP server manages calls on the network, receives requests from VoIP clients to establish and terminate calls.  

The most popular open source SIP server is Asterix (https://www.asterisk.org). To run Asterix in a company, you need to have a server with the Linux operating system installed. There are dedupe software packages in Linux distributions that contain the Asterix server. The best way to install the Asterix server is to download a specially prepared Linux distribution - freePBX (https://www.freepbx.org/downloads/ ). Asterix has many of the features of modern telephony including, among others: SMS, music while waiting/connecting, voicemail.