| In general, voice transmission over the Internet protocol (IP), or VoIP, means
transmission of real-time voice signals and associated call control information
over an IP-based (public or private) network. The term IP telephony is commonly
used to specify delivery of a superset of the advanced public switched
telephone network (PSTN) services using IP phones and IP-based access,
transport, and control networks. These networks can be either logically overlayed
on the public Internet or connected to the Internet via one or more gateways
or edge routers with appropriate service protection functions embedded
in them. In this book, I use VoIP and IP telephony synonymously, most of the
times.
This book grew out of my participation in many VoIP-related projects over
the past several years. Some of the early projects were exploratory in nature;
oscillators had to be used to generate certain tones or signals, and oscilloscopes
were used to measure the dial-tone delay, call setup time, and voice transmission
delay. However, as the technology matured, a handful of test and measurement
devices became available. Consequently, we turned out to be better
equipped to make more informed decisions regarding the computing and networking
infrastructures that are required to implement the VoIP service. Many
of the recent VoIP-related projects in the enterprise and public network industries
involve specifying a VoIP service design or upgrading an existing VoIP
service platform to satisfy the growth and/or additional feature requirements of
the customers. These are living proof of the facts that all-distance voice transmission
service providers (retailers and wholesalers) and enterprise network
designers are seriously deploying or considering the deployment of VoIP services
in their networks. |
