 is available. If the mobile station has stored a valid P_TMSI in the SIM, the mobile station derives a foreign TLLI from that P_TMSI and uses it for transmission of the following messages: ATTACH REQUEST message of any GPRS attach procedure RA UPDATE REQUEST message procedure if the mobile station has entered a new RA Any other GMM message is transmitted using a local TLLI derived from the P_TMSI or directly using a random TLLI, which means no valid P_TMSI is available. When the mobile station does not have a valid P_TMSI stored (that is, the mobile station is not attached to GPRS), the mobile station may use a randomly selected random TLLI for transmission of the ATTACH REQUEST message of any GPRS attach procedure. Upon receipt of an ATTACH REQUEST message, the network assigns a P_TMSI to the mobile station, derives a local TLLI from the assigned P_TMSI, and transmits the assigned P_TMSI to the mobile station. Upon receipt of the assigned P_TMSI, the mobile station derives the local TLLI from this P_TMSI and uses it for addressing at lower layers. In both cases, the mobile station acknowledges the reception of the assigned P_TMSI to the network. After receipt of the acknowledgement, the network uses the local TLLI for addressing at lower layers. 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. Mobile Station to SGSN Interface Chapter 8 Yet, another type of TLLI is available called the anonymous access request (auxiliary TLLI). In order to activate an anonymous PDP context, the mobile station sends an ACTIVATE AA PDP CONTEXT REQUEST message to the network. As long as no auxiliary TLLI is allocated by the network to the mobile station, a random TLLI is used for addressing on the lower layers. How the TLLI Is Transmitted TLLI is not carried in an LLC frame or GMM message, but is carried in the RLC/MAC blocks on the Un m interfaces and in the B