th a Cancellation Type set to Update Procedure message. The old SGSN acknowledges with a Cancel Location ACK message (IMSI). 8. The HLR sends an Insert Subscriber Data message (IMSI, GPRS subscription data) to the new SGSN. If all checks are successful, then the SGSN constructs an MM context for the mobile station and returns an Insert Subscriber Data ACK message (IMSI) to the HLR. The HLR acknowledges by sending an Update Location ACK message (IMSI) to the new SGSN. 9. The SGSN allocates a new P_TMSI and sends it in the RA Update Accept (new P_TMSI, LLC ACK) message. 10. The mobile station acknowledges the new P_TMSI with an RA Update Complete (P_TMSI, LLC ACK) message. SNDCP Layer 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 will therefore be possible without changing any of the lower-layer GPRS protocols. There- fore, all functions related to the transfer of N-PDUs are carried out transparently by GPRS network entities. The SNDCP is situated below the 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 network layer and above the LLC layer. It provides protocol transparency as it supports a variety of network layer protocols. The set of protocol entities sitting above SNDCP consists of commonly used network protocols. These all use the same SNDCP entity, which per- forms the multiplexing of data coming from the different sources before being sent via the services provided by the LLC layer. The NSAPI acts as an index for the appropriate PDP that is using the services of SNDCP. Each active NSAPI uses the services provided by the SAPI in the LLC layer and as such several NSAP