a major undertaking without systems that respond auto- matically to changing demands. On a Transmission Control Protocol/Inter- net Protocol (TCP/IP) network, each system must have an IP address, subnet mask, and router address (at a minimum) in order to communicate. Charging Gateway Function Make no mistake about it: The charging function is a crucial component of a GPRS network. Earlier the discussion led to the fact that the various operators are wrestling with the way to charge for the data aspects of GPRS. One Regional Bell Operating Company (RBOC) venture is planning an all-you-can-eat type service. For a flat rate, you can use as much data as you can with no added charges. Another is considering the use of the Japan- ese NTT DoCoMo model, whereby they charge a rate of the U.S. equivalent of $.0025 per packet of data sent. This constitutes a pay-as-you-go model. Still others are considering a pay-per-minute model that is similar to the telephony networks. Finally, some feel that the QoS or aggregate through- put is what should be charged at the end of the month. From experience in the field, the two that carry the most weight today are the DoCoMo model of charging per packet and the all-you-can-eat model. GPRS is a different kind of service from those typically available on today's mobile networks. GPRS is a packet-switching overlay on a circuit- switching network. The GPRS specifications stipulate the minimum charg- ing information that must be collected in the Stage 1 service description. These include destination and source addresses, usage of radio interface, usage of external packet data networks, usage of the PDP addresses, usage of general GPRS resources, and location of the mobile station. Because GPRS networks break the information to be communicated down into pack- ets, at a minimum, a GPRS network needs to be able to count packets to charging customers for the volume of packets they send and receive. Today's billing systems have difficulty handling charging for today's nonvoice ser- vices. It is 