7. Figure 8-6 The sequence in GSM ciphering. Frame # Frame # Cipher Code Cipher Code Uplink Uplink Ciphered Data #@*! Cipher Decipher 0100110 0100110 Cipher Code Cipher Code Downlink Downlink Ciphered Data &#% Decipher Cipher 0100110 0100110 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 Mobile Station to SGSN Interface Figure 8-7 The GPRS ciphering environment. Store Kc Store Kc Ciphered LLC Frames The performance requirements on the GPRS ciphering algorithm are expected to be similar to those of the existing A5 algorithm from the GSM architecture. The main difference is that ciphering for uplink and downlink transfers are independent. Therefore, the ciphering algorithm may be different. GPRS Mobility Management (GMM) GMM uses the services of the LLC layer to transfer messages between the mobile station and the SGSN. GMM includes functions such as GPRS attach, GPRS detach, security, cell update, routing area (RA) update, loca- tion update, PDP context activation, and PDP context deactivation. In addi- tion, GMM functions support the management of the three states (ready, standby, and idle) on both sides (mobile station and SGSN). The GMM informs the network of the whereabouts of the mobile station and provides confidentiality for the user. These are crucial functions that the mobility and session management functions operate at Layer 3. As Figure 8-8 shows, the GMM layers are transparent to the underlying layers and the BSS. 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 Figure 8-8 GMM layer. Relay BSSGP Network Network Service Service GSMRF GSMRF Temporary Logical Link Identifier (TLLI) With