Protocol converters, also known as gateways, are needed for communication between different stacks. They are used to convert the signal in one protocol to another to bridge network segments that use different MAC protocols. This allows machines from different manufacturers to communicate. Gateways that connect two IP-based networks, like TCP/IP with IPX/SPX, have two IP addresses, one on each network. The addresses of computers connected to the LAN are hidden behind the gateway. That is, the WAN can only see the gateway's IP address. Network Address Translation is performed to regulate the traffic between WAN and LAN.
Proton Exchange Membrane (PEM) is a semi permeable membrane generally made from ionomers and designed to conduct protons while being impermeable to gases such as oxygen or hydrogen. Their essential function into a proton exchange membrane fuel cell is the separation of reactants and transport of protons. They can be made from either pure polymer membranes or from composite membranes where other materials are imbedded in a polymer matrix. Proton exchange membranes are primarily characterized by proton conductivity, methanol permeability and thermal stability. One of the most common and commercially available PEM materials is Nafion. Many use polyaromatic polymers while others use partially fluorinated polymers.