d of the MAC header (2 bits). This bitmap enables the network to selectively retransmit received blocks with errors. In the acknowledged mode of UL transmission, the network regularly sends temporary acknowledgments to the mobile station. In any case, the sending window is 64 blocks (UL and DL). This window is shifted after each temporary or final acknowledgment message. All acknowledgment messages are transmitted on a PACCH (RLC/MAC con- trol block). Downlink (DL) Resource Allocation Downlink resources are allocated to the mobile station via the Packet Downlink Assignment message. This message will detail all the time slots that the mobile station may receive data on for a particular transaction. Each complete data transfer is allocated a TBF known by the identifier as already discussed (the TFI). The TFI is part of each uplink/downlink RLC data block and consists of 7 bits in the uplink and 5 bits on the downlink. The TFI for a specific mobile station is also specified in the Packet Down- link Assignment message. The mobile station has to receive and decode all the RLC/MAC blocks on its allocated time slots to ascertain if the TFI con- tained in the block is the appropriately assigned TFI. When the mobile sta- tion identifies a block with its allocated TFI, it will decode and process the data block. This is shown in Figure 6-21. The network initiates packet transfer to a mobile station in standby state by sending a Packet Paging Request message in the downlink PCCH (or PCH). The mobile station responds by requesting a channel. The Packet Paging Response message contains the TLLI as well as a complete LLC frame, including the TLLI. The mobility management state of the mobile station then becomes ready state. 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 Figure 6-21 Downlink data PCU Starts here if p