SSGP message on Gb interface. Figure 8-9 shows the format of the TLLI transfer: The TLLI is only transmitted on the RLC/MAC uplink data block when a GMM procedure is used (that is, when just the first blocks are sent during a signaling procedure). The Transaction Identifier (TI) bit indicates if a TLLI number is present in the frame. The TLLI is always transmitted in the BSSGP messages for all uplink and downlink packet data units and in many signaling procedures. The Information Element Identity (IEI) bytes indicate to the BSSG protocol what sort of information it should find in the following bytes delimited with the Length Indicator byte. RLC/MAC Header BSGGP Header Figure 8-9 How the TLLI is Payload Type Countdown Value MAC Header transmitted. Spare Octet 1 Length Indicator Octet 2 Length Indicator Octet 3 (optional) Length Indicator Octet M (optional) Length Indicator Octet M+1 Octet M+2 Octet M+3 Octet M+4 Octet M+5 RLC Data Length Indicator Octet N+1 Spare Spare Octet N (if present) 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 Mobility Management (MM) The Public Land Mobile Network (PLMN) provides information for the mobile station to Detect when it has entered a new cell or a new RA. Determine when to perform periodic RA updates. The mobile station detects when it has entered a new cell by comparing the cell's identity with the cell identity stored in the mobile station's MM context. The mobile station detects that a new RA has been entered by periodically comparing the routing area identity (RAI) stored in its MM context with that received from the new cell. The mobile station considers hysteresis in signal strength measurements. When the mobile station camps on a new cell, possibly in a new RA, this indicates one of three possible scenarios: A cell update is requir