ect to the Terms of Use as given at the website. Main GPRS Procedures Main GPRS Procedures Figure 5-15 Step 1. GPRS data flow to Src=a.b.c.d. the MS. Dest=1.2.3.4 a.b.c.d. IP Payload 1.2.3.4 Step 4. NSAPI=2 TLLI+NSAPI Original IP Src=a.b.c.d. Packet Dest=1.2.3.4 GPRS PLMN IP Payload Intra- Step 3. PLMN IP Step 2. Backbone TLLI=1, NSAPI=2 TID 1 GGSN IP TID 1 SGSN IP GGSN IP Address TLLI=2, NSAPI=2 TID 2 GGSN IP TID+GGSN TID 2 SGSN IP IP Address TLLI=3, NSAPI=2 TID 3 GGSN IP Original IP TID 3 SGSN IP Packet 1. Packets from the external network reach the GGSN. The GGSN looks up the tables to determine the particular SGSN address and TID for the mobile station that is the intended recipient of the packet. 2. The GGSN forms an IP datagram (packet) with the GGSN IP address as the source address and the SGSN IP address as the destination address and the original IP packet inside. The packet also contains the TID. 3. The SGSN maps the TID and SGSN to the corresponding TLLI and NSAPI values at the table entries. At this point, the SGSN knows where the mobile station is and to which network application it must route the packets. 4. The SGSN takes the original IP packet, adds a header with the NSAPI and TLLI, and forwards it to the mobile station. The SNDCP layer at the mobile station strips off the header and sends the packet to its associated network layer application. This sequence assumes that an active PDP context is open. In the event that no PDP context is established for the mobile station, the need may arise for the network to initiate a PDP context. First, a context is estab- lished between the GGSN and the SGSN to which the mobile station is attached. Then, the flow of events is as previously listed. 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 Mobile-Initiated Packet Data Protocol Context Deactivation To in