s with minimum changes to the Network Subsystems (NSS). These added radio solutions could include techniques such as Code Division Multiple Access (CDMA) or ANSI-136 + from the North American standards. The movement to a Uni- versal Mobile Telecommunications System (UMTS) is another possibility where the Universal Terrestrial Radio Access Network (UTRAN) is intro- duced. The LLC connection can be used to transfer point-to-point and point- to-multipoint data between the mobile station and the SGSN. LLC is designed to support many Layer 3 protocols, such as those shown in Fig- ure 8-1. Subnetwork-Dependent Convergence Protocol (SNDCP) Network layer protocols are intended to operate over services derived from a wide variety of subnetworks and data links. GPRS supports several net- work layer protocols providing protocol transparency for users of the ser- vice. The introduction of new network layer protocols to be transferred over GPRS is possible without any changes to GPRS. This is the role of the Sub- network-Dependent Convergence Protocol (SNDCP) layer. Figure 8-1 SNDCP SNDCP The LLC supports multiple protocols at Layer 3. Relay BSSGP Network Network Service Service GSM-RF GSM-RF 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 GPRS Mobility Management/Session Management (GMM/SM) GPRS Mobility Management/Session Management (GMM/SM) protocol supports mobility management (MM) functionality such as attach and authentication, and transport of session management messages for func- tions such as PDP context activation and deactivation. Short Message Service (SMS) The Short Message Service (SMS) uses the services of the LLC layer to transfer short messages between the mobile station and the SGSN. LLC Support The LLC layer supports the following functions: Service primitives enabling the transfer of SNDCP pr