nterfaces added to a GSM net- work in support of the GPRS services, the operators can actually get into the packet data business without major overhauls to their networks. The main investments are in software in many of the existing network components. The few actual hardware pieces are not SO expensive as to pre- vent widespread acceptance and implementation of the data networks. In the next chapter the focus will leave the hardware components and empha- size the main procedures used within a network to efficiently use resources and to allocate radio services to the data user. 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 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 Main GPRS Procedures Main GPRS Procedures Chapter 5 Objectives When you complete the reading in this chapter, you will be able to Describe the main components of the main functions of mobility management. Describe the mobile-initiated attach and detach procedures. Understand when the network performs an attach or detach procedure. Discuss the role of the SGSN in the procedures. Understand the three states of the mobile in GPRS. Mobility Management (MM) Before a mobile station (MS) can send data to a corresponding host, it must attach to a Serving GPRS Support Node (SGSN). An attachment procedure (GPRS attach) between the mobile station and the network is conducted and a Temporary Logical Link Identifier (TLLI) is assigned to the mobile station. Actually, the mobile uses the TLLI after the network assigns a Packet Temporary Mobile Subscriber Identity (P_TMSI). The mobile chooses the TLLI after being assigned the P_TMSI. After attaching, one or more routing contexts for on