ontexts; the PDP contexts are actually deleted in the Gateway GPRS Support Node (GGSN). The mobile station detaches by sending a detach request (detach type or a switch off) message to the SGSN. The detach type may include such things as detach for GPRS purposes only, IMSI detach (a GSM function), or both. Detach Type-GPRS-Only, IMSI-Only, or Combined If GPRS detaches, the active PDP contexts in the GGSN regarding this par- ticular mobile station are deactivated by the SGSN sending a Delete PDP Context Request message to the GGSN. The GGSN acknowledges with a 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 5-7 MS-initiated GPRS detach procedures. GPRS Detach Request Detach type, Switch Off Delete PDP Context Request Delete PDP Context Response GPRS Detach Accept Delete PDP Context Response. If the switch off indicates that the detach request is not due to a switch-off situation, the SGSN sends a GPRS Detach Accept message to the mobile station. Figure 5-7 shows the mobile station- initiated detach procedures, where the steps indicate the type of detach indicated. Network-Initiated GPRS Detach When necessary for the network to detach a mobile station, the SGSN informs the mobile station that it has been detached by sending a Detach Request (Attach Indicator) to the mobile station. The Attach Indicator indi- cates if the mobile station is requested to make a new GPRS attach and per- form PDP context activation procedures for the previously activated PDP contexts. If so, the GPRS attach procedure is initiated when the GPRS detach procedure is complete. Figure 5-8 shows the network-initiated detach procedure. The active PDP contexts in the GGSN are deactivated by the SGSN. The mobile station sends a GPRS Detach Accept message back to the SGSN anytime after the Detach Request message. Downloaded from Digital 