TID 2 SGSN IP TID 3 SGSN IP Figure 5-11 The mobile-initiated PDP activation. Tunnel Activate PDP Context Request (NSAPI, PDP type, PDP address, Create PDP Context QoS requested, APN) Request NSAPI, PDP type, PDP, QoS, APN Security Functions Create PDP Context Response Activate PDP Context Accept (PDP address, QoS (PDP type, PDP address, QoS negotiated) Negotiated) PDP address, whether it is a static or dynamic address (IP address) Requested QoS (best effort is all that is currently available, but will get to specific QoS in the future) Access Point Name (APN) (optional) to select a certain GGSN, either the IP address or logical name is used PDP configuration options 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 Main GPRS Procedures The mobile station only exchanges messages with the SGSN, which acts as a relay to the GGSN. The SGSN performs the following: Check the subscription data that was stored in the SGSN during the GPRS attach to determine if the mobile station is able to activate the PDP address. Insert the NSAPI along with the GGSN address in its PDP context. Return an Activate PDP Context Accept message to the mobile station. Become ready to route PDP packets (PDUs) between the GGSN and the mobile station. Continuing the process of the mobile-initiated PDP context activation, and using Figure 5-12 as a guide, the next steps are considered. When the SGSN receives an APN from the mobile station, it checks to see if the APN ends with .gprs. If it does, the last three labels of the APN that represent the APN Operator Identifier are removed and the remaining labels that make up the APN Network Identifier are used for comparison with the sub- scription record. In the second step, when the SGSN has validated the mobile station parameters, it must determine which GPRS gateway to select for the given APN. Therefore, it