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Virtual Private Networks (VPNs) are encrypted tunnels carrying packetized data between remote sites. VPNs may use private lines or the Internet via one or more Internet Service Providers (ISP). VPNs are implemented in both dedicated hardware and software, but they can also be integrated as an application to existing hardware and software packages. A common example of an integrated package is a firewall product that can provide a barrier against unauthorized intrusion, as well as perform the security features needed for a VPN session.
The encryption process can take from less than 1 millisecond to 1 second or more, at each end. VPNs represent a significant source of delay and, therefore, negatively affect voice performance. As most VPN traffic runs over the Internet and there is little control over QoS parameters for that traffic, voice signals may suffer packet loss, delay, and jitter. A VPN provider may be able to guarantee an acceptable level of service, but before implementing VoIP with a VPN, test the VPN network to make sure it meets the minimum delay, jitter, and packet loss requirements.
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