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P2302R-P1 Support Notes
All contents Copyright 2007 ZyXEL Communications Corporation.
113
How does Voice over IP work?
Basically VoIP is a technic to send voice information in digital form in discrete packets over digital network
rather than by using traditional circuit switch (PSTN). To do so we will need an analog to digital converter on
sender side to translate the voice (analog signal) to digital than transmit it, and on the receiver end it will also
need an analog to digital converter to covert the digital signal back to analog to the person being called can
heard the voice.
Why use VoIP?
Traditionally telephony carrier use circuit switching for carrying voice traffic. As circuit switching is designed
to carry voice and it does it very well. Than why use IP for voice? As broadband booms, and technology
evolve. People now want to communicate through various way not just voice such as email, instant
messaging, video and so on. Traditional telephony can not evolve as quickly as the demand and develop new
feature on circuit switch takes much time and money. IP is an already exist standard and many type of service
already runs on IP, by using IP as a platform integrate service is now possible and low cost where traditional
circuit may take long time to achieve.
What is the relationship between codec and VoIP?
In order to transfer voice (analog signal) over IP it first need to be digitized. Codec is a technic to digitize
analog signal to digital and vice versa. There are various speech codec available and can be used with VoIP
each with it's advantage and disadvantage.
What advantage does Voice over IP can provide?
The advantage of VoIP is it can provide advance services such as joining e-mail, instant messaging, video,
voice mail all together. Where current circuit switching (PSTN) can not.
What is the difference between H.323 and SIP?
H.323 and SIP are proposed by different group Session Initiation Protocol (SIP) is a standard introduced by the
Internet Engineering Task Force in 1999 to carry voice over IP. Since it was created by the IETF, it approaches
voice and multimedia from the Internet, or IP, perspective of view. Where as H.323 emerged around 1996, and
as an International Telecommunication Union standard it was designed from a telecommunications perspective.
Both standards have the same objective - to enable voice and multimedia convergence with IP protocols.