IP security is provided in a virtual private network using network address translation by performing one or a combination-of the three types of VPN NAT, including VPN NAT type a outbound source IP NAT, VPN NAT type c inbound source IP NAT, and VPN NAT type d inbound destination IP NAT. The switch establishes a communication session using one of these networks and then switches the communication session to the other one of these networks in response to stored metrics, user request, or other criteria. 0undec-7-ene; 1,4-diazabicyclo2. The use of light guides eliminates the use of free space optical elements, enabling the creation of more compact light sources. The transmission axis of one of the first and second polarizers is set approximately in parallel to a liquid crystal orientation direction.