unications infrastructure now. In the 4G network, each node will be assigned a 4G-IP address (based on IPv6), which will be formed by a permanent "home" IP address and a dynamic "care-of" address that represents its actual location. For example, say that a device on the Internet, a computer, wants to communicate with a device on a wireless network, a mobile phone. The computer will send a packet to the 4G-IP address of the mobile phone, targeting its home address. A directory server on the mobile phone's home network will forward the packet to the mobile phone's care-of address through a tunnel, mobile IP. The direc- tory server will then also inform the computer of the mobile phone's care-of address (the real location) SO it can send subsequent packets directly to the mobile phone. 4G concerns involve cost and the compatibility of various applications, such as three-dimensional virtual reality and interactive video hologram images. 4G will increase interactions between corroborating technologies. For example, the smart card in your telephone will automatically pay for goods as you pass the linked pay- ment kiosk, or the smart card will tell your car to warm up in the morning because your phone has noted you leaving the house or turning off your alarm clock. Developments for 4G began in 2002, and there are many standards and tech- nologies under consideration, many of which are still in the development stages. Therefore, no one can really say what the future 4G network will look like and what services it will offer. Keep in mind that today's pace of development is SO rapid that often a given technology doesn't have a chance to become pervasive in the marketplace before its successor is already named. And that very well may be the case with 3G and 3.5G. Industry visions looking forward may be characterized as involving a horizontal communications model where different access technolo- gies will be combined on a common platform to complement each other in an opti- mum way for different service requirements and radi