oes not imply that the operators will offer the free Internet Service Provider model seen on the fixed Internet. Users do not pay a fixed monthly charge so the network operators rely on advertising sales on mobile portal sites to make money. A premium exists for the sake of being mobile and the costs associated with acquiring bandwidth dictates some form of charge- back system. Given the additional customer care and billing complexity associated with mobile Internet and nonvoice services, network operators would be ill-advised to reduce their prices in such a way as to devalue the perceived value of mobility. The implementations by many vendors occurs on a Sun Enterprise Server (like the E250) hardware running some form of charging and accounting software. The Charging Gateway Function, shown in Fig- ure 4-15, is composed of three main functional areas: Billing Record Collector This entity collects billing records from the GPRS nodes. In the first GPRS release, only the GGSN Billing Record Collector was available. Flow Aggregation Processor This entity aggregates several billing records produced during a PDP session (such as several Start and Stop Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Function of GPRS Elements Chapter 4 Figure 4-15 The Charging Billing Center Gateway Function. GPRS Core Network Collector Billing Files Transfer Aggregator Distributor Billing Records: Get Billing Files -PDP session duration in seconds GPRS QoS negotiated -Input Octets -Output Octets records due to time or volume conditions) into a single GPRS accounting record. The format for this aggregated record is called a Network Accounting Record (NAR). The billing records coming from different collectors cannot be aggregated (two different collectors are seen as two different billing streams by an aggregator). Flow Data Distributor This entity is responsible f