t dissimilar to the GSM archi- tecture, although they deal with the packet data channels and control func- tions. One can see several similarities between the GSM and GPRS architectures. As stated earlier, GPRS is merely an overlay of GSM SO the channel definitions are close. 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. System Architecture 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. CHAPTER Function of GPRS Elements Function of GPRS Elements Chapter 4 Objectives When you complete the reading in this chapter, you will be able to Describe the locations for the CCU. Describe the four different types of channel codec services. Understand where the options are for locating the PCU. Discuss the role of the GGSN and SGSN. Understand the way that the HLR and VLR interact in the GPRS network. For the first time, General Packet Radio Service (GPRS) fully enables mobile Internet functionality by permitting interworking between the existing Internet and the new GPRS network. Any service that is used over the fixed Internet today (such as File Transfer Protocol [FTP], Web brows- ing, chat, e-mail, and telnet) will be as available over the mobile network because of GPRS. In fact, many network operators are considering the opportunity to use GPRS to help become Wireless Internet Service Providers (W-ISPs) in their own right. The World Wide Web is becoming the primary communications interface -people access the Internet for entertainment and information collection, the intranet for accessing company information and connecting with col- leagues, and the extranet for accessing customers and suppliers. These are all derivatives of the World Wide Web aimed at connecting different com