s a GPRS RA update and GPRS cell selection and reselec- tion locally. At this point, if the subscriber wants to request e-mail or a Web page, a PDP context must be activated in advance. If the standby timer (for the mobile station or SGSN) expires in this state, the mobility management contexts in both the mobile station and SGSN independently return to the 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. Main GPRS Procedures Chapter 5 Figure 5-3 Inactive The PDP context mode for the MS in active or idle modes. Deactivate PDP Activate PDP Context or MM Context State Change to IDLE Active PDP Context State Machine idle state and may be deleted. Figure 5-3 shows the conditions of the PDP context management mode. GPRS Attach A GPRS mobile station is not reachable or known by the network until the mobile station performs the attach procedure and switches into the ready mode. To attach to the network (actually the SGSN), the mobile station pro- vides its identity and indicates which type of attach procedure is to be performed: GPRS attach Needs the mobile station's P_TMSI and the routing area identity (RAI) where the mobile is located IMSI attach Specific to GSM, but may be performed via GPRS if a TMSI or P_TMSI are not already assigned to the mobile station IMSI/GPRS attach (for class A and B mobile stations) Will possible in a later release of GPRS In the ready state, Both the mobile station and the SGSN have established mobility management contexts for the subscriber's International Mobile Subscriber Identity (IMSI), which is the primary key to the GPRS subscription data stored in the Home Location Register (HLR). The mobile station may send and receive data protocol data units (PDUs) that are nothing more than packets. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill