How Does VoIP Work

Even though VoIP is a relatively new technology, it’s hard to imagine the world without it. Owing to the technology, people can now make phone calls anywhere at any time. The technology is revolutionary and is expected to get even better in future. However, despite its nearly universal applicability, most people don’t know much about VoIP. Perhaps this is due to complex concepts used in this technology or the technical languages used by VoIP experts to explain what VoIP is and how it works. But this article will be different. There will be no use of technical terminologies, and hopefully, with enough clarity, most people will understand what VoIP is, its importance, and how it works.

With a microphone or Microsoft’s sound recorder, people can record, edit and play their voices on their computers. The voice recording process involves sampling of voice and storing those ‘voice samples’ in a file or in the memory of the computer. After storage, the computer plays the audio samples such that listeners can hear what was recorded. VoIP employs the same concept, but the only difference is that voice samples are not stored locally. Instead, the audio samples are stored in another location and played there.

How VoIP Works

In simple terms, VoIP is based on the same concept as voice recording on a computer. However, VoIP is more sophisticated and requires much more for it to work. When voice recording takes place on a computer, it records only a limited frequency range and uses simple CODECs to convert analog signals to digital audio. The computer might also compress the voices so that they occupy less space.

Things are different when it comes to VoIP. For VoIP, the CODECs are more sophisticated and are optimized to compress the sound, which helps reduce the bandwidth used in the uncompressed sound stream. The CODECs used in this technology are enhanced to improve spoken words with the loss of sounds outside the frequency of human sound. Music or other sounds passed through VoIP CODECs do not sound fine. However, there are advanced CODECs out there that work perfectly when used for speech or music.

After the audio is recorded by the computer, which is normally in another location, and compressed into small samples, the audio samples are collected in large groups and placed into data packets for transmission over the communication network (IP network). The whole process is known as packetization. According to VoIP experts, a single data packet contains ten or more milliseconds of audio, with 20 and 30 milliseconds being the most common.

VoIP experts have tried to explain what packets are but end up confusing people even more. However, one expert, Vint Cerf, explains what packets are in a way that is very easy for anyone to understand. According to him, if VoIP experts want people to understand what packets are, they should make them think of packets as postcards sent via postal mail. Just like packets, postcards contain a limited amount of information. To send a very long message, therefore, one has to send a lot of postcards. Also, for one to understand the message in the postcards, one has to organize the received postcards in order. Packets work in the same way.

Packetization is complicated, and some IP data packets may get lost in the process. To compensate for the lost packets, the CODECs fill the gaps with audios that make sense to the human ear. VoIP specialists call this process packet-loss concealment (PLC). Recent advancements in VoIP systems allow packets to be sent multiple times to reduce packet loss. The method of sending packets multiple times is referred to as redundancy.

Specialists also use a forward-error correction (FEC) to prevent packet loss. Forward-error correction (FEC) includes some information from previously transmitted IP packets in the subsequent IP packets. The method uses mathematical operations to reconstruct lost packets using information bits from other neighboring packets.

Just like postcards sent through a post office, packets can sometimes be delayed, and this is causes problems in VoIP systems. Why? VoIP systems are designed to play voice packets once they get into the system. Delays mean the information will be too old for the VoIP systems to play, and the old voice packets are discarded. Can this disrupt the phone call? Discarding old packets is acceptable although this can result in a choppy voice. Fortunately, this doesn’t interfere much with a phone call because PLC and FEC algorithms help provide good audio quality.

Even though delays can increase or decrease during the course of a phone call, the VoIP systems are designed to expect delays. Delay, in this case, means it takes longer for a recorded voice spoken by the first user to reach the second user on the other end. VoIP systems keep on evolving, and better versions are being developed. However, jitter (variation in delay) is still common and should be addressed. In general, a good network should have an end-to-end delay below 100ms. If one is using satellite systems to make a phone call, delay of up to 400ms is acceptable. Like mentioned before, jitter causes temporary glitches so future VoIP devices must solve this problem.

Future VoIP devices should come with jitter buffer algorithms. This means that a certain number of voice packets are lined up before the play-out, and the length of the line may be increased or decreased over time to reduce the number of rejected and late voice packets or to reduce end-to-end delay. During a phone call, the VoIP system may need to adjust its jitter buffer management behavior as delay increases or decreases.

How do video calls work? Video call works the same way as voice calls. During a video call, information transmitted through the camera is broken into small pieces, compressed with special communication network compressor and de-compressor algorithms and placed into small data packets. Of course, video telephony has its unique issues such as higher bandwidth requirements and frame refresh. However, the basic principles used in VoIP systems are still used in video telephony.

VoIP is not all about sending audio and video packets over the interment. There must be a protocol that defines how computers find each other and how information will be shared in order to transmit voice packets smoothly through the communication devices. A payload format is also required for the contents of the media packets.

The article focused on computers when explaining how VoIP works. However, readers should note that VoIP is not limited to laptop or desktop computers. VoIP can be used in a variety of devices, including gateways, ATAs (Analog terminal adapters) and IP phones. There are also VoIP systems out there that run on smartphones and tablet. If you are interested in VoIP, you should check out some free VoIP applications available on the web.

VoIP software is easy to download and takes about three to five minutes to set it up. Should you throw away your old device to migrate to VoIP? Like we mentioned, a large number of devices support VoIP. Check if your device can support VoIP before you throw it way. If it can’t, you can consider buying one that supports VoIP.

See also

Created by: avadtechpr, Last modification: Wed 30 of Aug, 2017 (21:02 UTC) by admin
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