Although this is a Cisco networks dedicated blog, I decided to start a series of tutorial posts about a general technology which is not directly related to Cisco but it is a field in which Cisco is again a major player. This is IP Telephony and Voice over IP (VoIP). The two terms, IP Telephony and VoIP, are related around the same concept but in my opinion they are not exactly the same thing. Many people refer to these two terms interchangeably but they are not exactly the same. So, before moving on lets clarify the difference between IP Telephony and VoIP.
The truth is that despite the long presence of the VoIP technology, its penetration is not very widespread. According to In-Stat/MDR company, in 2004 VoIP was used only by 12% of U.S. businesses, a figure which is estimated to reach 70% this year. At international level the percentages are even lower. It is worth noting that large companies have the highest penetration. Factors related to delay the penetration of IP telephony are issues related to attitude (commitment to traditional technology), while clearly related with the technological immaturity of the technology in some places and the high cost of transition to IP platform. The technology is now mature enough and affordable, so it will also have higher rates of market growth compared to previous years.
The use of IP telephony is not just in the business environment. Firstly, several alternative telecommunications companies use the IP technology to provide telephony services. Also, many traditional telecommunications companies around the world consider the gradual replacement of their networks by packet switched networks, in an effort to make better use of their telecommunications infrastructure. You should not also ignore the great potential that the penetration of IP telephony has in the consumer level. A great indicator is the phenomenal success of the Skype service, which allows users to make free VoIP calls, as registered users of the service has exceeded 24 million. They have already made their appearance similar services in the market and it is clear that the future will be more promising with the increase in penetration of broadband Internet.
The term VoIP or Voice over IP refers to the transfer of voice packets over networks based on Internet technology and, more specifically, the IP Protocol. The IP protocol on which the whole Internet is based on was created to implement the transmission of data in the form of data packets. This means that when a data document is transferred over the Internet is cut into small IP packets and sent over the network. When the document reaches its destination, the packets are joined again thus recreating the original document. The same logic applies if the data transferred corresponds to a voice conversation. The voice is digitized, chopped into packets of data transferred over the network via the IP protocol. At the destination the packets are rejoined to recreate the voice stream. Here we should make clear that VoIP refers to the transfer of voice over any IP network. Such a network is the Internet of course, but when considering VoIP it does not necessarily mean that we carry voice over the Internet only. It can be any IP-based network (such as a private corporate WAN network).
Requirements for quality in voice networks determine the maximum latency of 150-200 ms. A greater delay value usually reduces the quality of conversation significantly. The greatest amount of delay (30 milliseconds) is introduced by the G.723 codec, and the lowest delay (0.75 ms) is found in G.711 codec. It should be noted that the smallest propagation delay time is introduced by channel switching networks, and the greatest propagation delay is found in packet-switched networks (IP networks) due to buffering. In connection with this fact, the VoIP technology is less attractive for voice transmission over the Internet, than VoATM and VoFR. Nevertheless, VoIP quality over the Internet is quite acceptable for a corporate network that needs maximum of 4 -6 concurrent voice channels.
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