VoIP
November 2005
Would you like to call a relative or friend who lives across the country paying the same as you pay for a local call? How about talking for hours on the phone without worrying about the bill? This dream has become true thanks to VoIP! In this article you will understand what VoIP is and how this technology works.
What is VoIP?
VoIP (Voice over Internet Protocol) is a type of technology which allows the transmission of voice over IP, allowing high-quality calls to be made over the Internet. VoIP, also known as Voice over IP, has become more and more popular allowing more and more companies working with that kind of technology to be launched. Companies such as Netexperts, which is inserted in this market.
VoIP allows the telephone networks to “mix” with the data networks. In order to make a call before it was necessary to use a microphone, speakers or headphones and appropriate software, and then, the call was made, through the computer, to conventional phones. Now VoIP adapters can be used. Those adapters are connected to the broad band and allow the calls to be easily made through a conventional telephone.
Companies have also been applying VoIP technology into their PABX (Private Automatic Branch Exchange), the well-known system of telephone branches, creating considerable reduction of expenses.
How does VoIP work?
In order for the voice transmission to be made possible, VoIP captures the voice, which so far has been transmitted analogically, and transforms it into packets of data, that can be sent over any TCP/IP (Transport Control Protocol/Internet Protocol) network. It is, therefore, perfectly possible to work with those packets on the Internet. When the destination receives the packets, they are re-transformed into analogical signals and transmitted to an environment in which it is possible to hear sound.
In spite of having gained distinction only recently, VoIP is not new technology. It had been used even before the popularization of the Internet and it was once considered a failure, since the speed of data transmission was low at the time and, therefore, prevented it from becoming functional in most networks.
In order for VoIP to become a viable technology, it was (and it is) necessary to invest in QoS - quality of service. One solution for that would be to increase the broad band, that is, to increase the speed of data transmission and reception. As broad band Internet has become more and more common, especially at companies, VoIP has taken advantage of that. However, speed alone is not enough.
Given that fact, many companies working at the field have started researching solutions which guarantee the best possible quality of communication via VoIP. This is a natural step, since it is the company (or group of companies) which has the best results that definitely leads the war for clients. This situation has generated a series of solutions for VoIP.
Despite the several VoIP standards, virtually every company has adopted RTP, or Real Time Protocol, which, basically, tries to get the packets delivered at the same order they were sent. RTP orders the data packets so that the transmission of data in real time is made possible. If there is a delay in the delivery of any packet, RTP causes an interpolation between the “gap” left by the packet and it is not delivered.
For instance, imagine that, in order to transmit the word NETEXPERTS, a packet for each letter has to be used. If the packet of the letter X is delayed, it is better that the recipient receives “NETPERTS” than “NETEPERT”. The delay of packets can occur because the packets can take different paths in order to get to the same destination. This is not a problem if a file is being transmitted, since its packets are “fitted” in the recipient. However, when using real time voice and video, that cannot happen.
According to such fact, it is clear that RTP is a very useful resource in applications involving sound and video. Due to that, its functioning is connected to another protocol, RTCP (Real Time Control Protocol). RTCP is responsible for the compression of the data packets as well as their monitoring.
Because improvements are still necessary, IETF (Internet Engineering Task Force), responsible for RTP and RTCP, suggested the application of RSVP (Resource ReSerVation Protocol), which has as its main function the allocation of a part of the available band for the transmission of voice.
There are also the codecs, extra protocols which add functionality and higher quality to the communication. Among which there are G.711, G.722, G.723, G.727, and others. What differentiates them is the algorithms used, the average delay, and especially, the quality of voice. G.711 is considered to be the best in quality of voice. All of the codecs are recommended by ITU-T (International Telecommunications Union - Telecommunications standardization sector) and they generally work together with another protocol: CRTP (Compressed Real-Time Protocol), responsible for the improvement of the packet compression and, therefore, providing quality to VoIP.
In order for the interconnection of conventional telephone networks and VoIP to be possible, Gateway is generally used. Gateway is responsible for the conversion of the analogical signal into digital and vice-versa and besides that, Gateway also converts the telephone call signals. There is also Gateway Controller, or Call Agent, which is responsible for controlling the calls made through Gateway.
For the long distance calls, the equipment used is known as Gatekeeper. It manages a series of other equipment and it can, besides other functions, authorize calls and control the band width used. Therefore, Gatekeeper can be understood as a telephone switch for VoIP.
IP Telephony
It is very common for VoIP to be mistaken by IP Telephony, however, they are different. IP Telephony is a type of “improved version” of VoIP. In fact, for a service to be characterized as IP Telephony, it is necessary that this service present quality and functionalities that are, at least, equivalent to the conventional telephony services.
VoIP technology basically converts the voice signals (analogical) into the digital format, using both data infra-structure and analogical infra-structure. IP Telephony also uses specific telephone appliances as well as computer networks such as the Internet. Such devices are generally sophisticated enough for the transmission of voice in real time in a level of quality that surpasses the conventional telephony. The most interesting fact is that IP Telephony can get to this level of efficiency without the need of telephone switches and it can also offer integration with other data services, such as video and e-mail.
A final word
As it became more and more popular, VoIP was seen as the “enemy” of traditional telephony companies, but it was soon realized that this technology is, in fact, a new product to be explored. Besides the advantages concerning costs, there is still the constant increase in quality. There are cases in which the sound quality of VoIP surpasses the quality of a conventional telephone call.
Nowadays, VoIP technology is not used exclusively by companies. Thanks to Skype software, developed by Niklas Zennström (the creator of KaZaA), the use of voice over IP is also available to home users. This proves that VoIP can become one of the Internet phenomena, just like the e-mail. We will certainly witness a great change in the way we use the telephone.
Netexperts could not be out of this market change and it brings its clients MinasVoIP, which offers VoIP telephony for R$129 a month with free calls to 35 countries.