nformation transfer NSAPI 2 Figure 8-3 SAPI 1 The LLC identifiers create a DLCI. SAPI 2 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 GPRS Mobility Management SNDCP Figure 8-4 The functions of the Layer 3 LLEs. LLC Layer Logical Link Entity Logical Link SAPI=7 Logical Link Entity Logical Link SAPI=11 Entity Management Logical Link SAPI=9 Entity Logical Link SAPI=5 Entity Entity Logical Link SAPI=3 Entity SAPI=1 Multiplex Procedure LLC Layer BSSGP RLC/MAC Layer BSSGP Layer RLC/MAC BSSGP Flow control Frame error detection The LLE analyzes the control field of the received frame and provides appropriate responses and layer-to-layer indications. Functions of the mul- tiplex procedure in the LLC layer are as follows: On frame transmission, 1. Generates and inserts the FCS 2. Performs the frame ciphering function 3. Provides SAPIs On frame reception, 1. Performs the frame decipher function and checks the FCS 2. Distributes the frame to the appropriate LLE 3. Performs GPRS deciphering function 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 The Logical Link Management Entity (LLME) manages the resources that have an impact on individual connections. One LLME exists per TLLI. Functions provided by the LLME are Initializing the parameters to be used Error processing Invoking connection flow control Mapping the LLC Frame You can find the SAPI parameter in the address field of the LLC frame. Fig- ure 8-5 shows the different values the SAPI can take in function of the ser- vice required. Note that TLLI is not transmitted in LLC frames. The length of the LLC header depends 