yer in the mobile station receives an LLC frame that is ready for transfer. The mobile station communicates with the network and ultimately receives a TFI that will be used to identify all consecutive (that is, one data burst) RLC blocks that are transferred. The MAC layer then segments the LLC frame and encapsulates it with an RLC header containing the TFI. Once all RLC blocks have been transferred and acknowledged (in the ACK mode), the TFI is released. At this point, the radio resources are not required; the TBF no longer exists. Idle The mobile station has no data to transfer even though GPRS data services remain active. Data Burst 2 The mobile station has additional data to transfer. It notifies the network in order to establish another TBF. The TFI corresponding to this TBF will most likely be different from that corresponding to the first TBF. Again, once all RLC blocks have been transferred and acknowledged, the TFI is released and the TBF disappears. This procedure can happen repeatedly until the GPRS service is complete. Figure 6-26 TFI=1 Identifiers at the RLC Block MAC Layer. 1. Data Burst TBF 1 (No Packets for Transfer) 2. Idle TFI=2 3. Data TBF 2 Burst 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. Radio and MS-PCUSN Interfaces Chapter 6 Channel Allocation and the MAC Layer The uplink state flag enables the network to control the multiplexing of mobile stations. The USF field is included in the header of each RLC/MAC data block sent on the downlink. It designates the mobile that can transmit data in that particular time slot of the next uplink radio block. Eight possi- ble USF values can be assigned, SO a maximum of eight users can be mul- tiplexed in the same time slot. Three allocation modes are possible in the MAC layer: fixed allocation, dynamic allocation, and extended dynamic allocation. Each of these modes applies to th