[转载]Voice over IP Security —— A layered approach

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Integration of communication services into the IP network infrastructure, and the Internet especially, is natural course that was started long ago with e-mail, continued with instant messaging and now taken one-step further with integration of standard, classical services like telephony. Voice over IP – the transmission of voice over packet-switched IP networks – is one of the most important emerging trends in telecommunications. Two factors have an important role in the growing popularity of Voice over IP networks: the cost savings factor, inherent to the migration from standard to Voice over IP networks, and the flexibility factor that allows new services and new applications to be added to standard telephony services (video transmission, conferences, etc). With 2005 declared as the Voice over IP (VoIP) year and with predictions of fairly large budgets attributed to VoIP projects in the near future, this technology seems set to replace classic, circuitbased telephony in the near future.