ure 5-9: 1. The mobile station sends a PDP context activation request to the SGSN. The SGSN chooses the GGSN based on information provided by the mobile station and other configurations and requests the GGSN to create a context for the mobile station. The SGSN will select a GGSN that serves the particular type of context needed (such as one for IP network access and one for X.25 access) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com Copyright © 2004 The McGraw-Hil Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Main GPRS Procedures Main GPRS Procedures Figure 5-9 The steps in Radio 1. activating a PDP Frame context. Relay 1.2.3.4 NSAPI=2 GPRS PLMN Intra- PLMN IP Backbone 3. The GGSN replies to the SGSN with the TID information. It also updates its tables wherein it maps the TID and the SGSN IP addresses with the particular mobile associated with them. 4. The SGSN sends a message to the mobile station informing it that a context has been activated for that particular mobile. The SGSN also updates its tables with the TID and the GGSN IP address with which it has established the tunnel for the mobile. Figure 5-10 shows the table entries for the SGSN and the GGSN. Mobile-Initiated PDP Data Protocol Context Activation The PDP context activation aims to establish a PDP context between the mobile station and the network, as shown in Figure 5-11. It may be per- formed automatically or manually depending upon the manufacturer's implementation and configuration. The mobile station first sends an Acti- vate PDP Context Request message that contains the following: NSAPI PDP type 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 5-10 TID 1 GGSN IP The SGSN and GGSN tables. TID 2 GGSN IP Table TID 3 GGSN IP TID 1 SGSN IP Table 