The LSN architecture of an ISP using Citrix products consists of subscribers (Internet users) in private address spaces accessing the Internet through a NetScaler appliance deployed in ISP’s core network. Subscribers are connected to the ISP through the ISP's access network. Usually, subscribers for commercial use of the Internet are directly connected to the ISP's access network. Serving those subscribers requires only one level of NAT (NAT44).
Noncommercial subscribers, however, are typically behind customer-premises equipment (CPE), such as routers and modems, that also implements NAT. These two levels of NAT create the NAT444 model. Deploying a NetScaler appliance in an ISP’s core network for LSN functionality is transparent to the subscribers and requires no configuration changes to subscribers or the CPEs.