How does VoIP work? A technical guide to functional VoIP

By now, you probably have a general idea of what VoIP is, but do you understand how it works? Do you know how many bits are in a conventional PCM voice sample or what "look-ahead" is used for? Do you know which two modes a caller can use to set up a call with SIP? If you don't know the answers to these questions, you will after reading SearchVoIP.com's technical guide to VoIP. Learn how call signaling and gateways work and why VoIP calls are particularly susceptible to delay and echo. Uncover the functional elements of SIP, H.323 and MGCP and why softswitches are not really switches at all.

By now, you probably have a general idea of what VoIP is, but do you understand how it works? Do you know how many bits are in a conventional PCM voice sample or what "look-ahead" used for? Do you know which two modes a caller can use to set up a call with SIP? If you don't know the answers to these questions, you will after reading SearchVoIP.com's technical guide to VoIP. Learn how call signaling and gateways work and why VoIP calls are particularly susceptible to delay and echo. Uncover the functional elements of SIP, H.323 and MGCP and why softswitches are not really switches at all.

 


CONTENTS

Section 1: How is transmitting voice different from sending data?
Section 2: What causes QoS problems with VoIP?
Section 3: How does VoIP work?
How do VoIP gateways work?
What is an IP packet?
Understanding VoIP delay
How do lost packets impact VoIP QoS?
Controlling VoIP echo
Section 4: What are media gateways and how do H.323, SIP, MGCP and other support protocols work?
How does H.323 work?
How does SIP work?
How does MGCP work?
How does Megaco or H.248 work?
Section 6: References

 

About the author:
Roger Freeman is an expert in telecommunications system engineering who has worked in telecommunications since 1946 when he became an aviation radioman in the U.S. Navy. Freeman later held several positions with ITT and served as the International Telecommunication Union’s regional planning expert for Northern Latin America in Quito, Ecuador. He  was also principal engineer with the Raytheon Company and started writing telecommunications books for John Wiley & Sons in 1973. His Fundamentals of Telecommunications is in its 2nd edition, and his two-volume work, Reference Manual for Telecommunication Engineers, is now in its 3rd edition.

This was last published in June 2006

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