How does VoIP work?
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Answer / guest
To understand how VoIP works, you will be taken through the
process of voice transmission from one end to the other.
The process starts with a person talking into the
mouthpiece on one end of a VoIP call.
This analog voice signal must first be sampled and
digitized. Voice sampling is usually done 8,000 times per
second (8KHz). In order to reduce bandwidth, a voice CODEC
is used. A voice CODEC is a compression/decompression
algorithm that is optimized for the voice frequency range.
The bit stream uncompressed is 64Kbps. By using an
available CODEC, the bit stream can be reduced to 8Kbps or
less.
In order for the compressed voice data to be sent over the
Internet, it must go through a process called
packetization. This is a packet consisting of a small
sample of the voice data (usually 10-30 milliseconds).
While being routed through the Internet, these packets can
get delayed or even lost. This can cause degradation in
voice quality. Simply put, there are various mechanisms in
place to compensate for these problems and help smooth out
the audio.
Once all the packets arrive on the listening end of the
call, they must be reassembled to their original state. The
packets are decompressed and converted from a digital to
analog voice signal.
| Is This Answer Correct ? | 11 Yes | 4 No |
Answer / pavan_mustyala
I will give example of end-to-end call in a SIP network.
SIP is Session Initiation Protocol which is signalling
protocol mainly taking care call establishment between end
parties. Initially a series signalling messages flow
between the end parties for connection establishment and
capabilities negotiation. INVITE,RINGING,ACKNOWLEDGE,etc.
After successful negotiation and acknowledgements, RTP
session is initiated between end parties and the RTP
packets carry the voice information. The voice data is
sampled at regular intervals of time, and
compressed/decompressed according to the CODEC used. Some
of the CODECs are G711, G723,G729,etc which differ in the
compression ratio thereby effecting the effective BandWidth
(BW). G711 uses more BW where G729 uses less compared to
G711. But QOS gets effected with type of CODEC used which
is the most challenging area in VOIP currently. G711
provides better QOS compared to G723 which provides better
QOS compared to G729.
In summary, RTP in conjunction with signalling protocols
like SIP paves the way for VOIP.
| Is This Answer Correct ? | 5 Yes | 0 No |
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