文末最后又详细介绍了虚拟专网和免费电话800业务。
Finally, the paper introduces virtual private net-work and free telephone (800) services.
文章提出了电话虚拟专网P_ VPN安全模型，其体系包括管理层、传输层和控制面。
This paper presented the virtual telephony network, P_VPN. The architecture of P_VPN includes management layer, transmission layer and control plane.
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