MAC header, one RLC data block or one RLC/MAC control block, and one Block Check Sequence (BCS). Some fields are specific to the uplink or to the downlink way. Figure 6-19 shows the data blocks side by side. 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 Radio and MS-PCUSN Interfaces USF in the MAC header of DL Blocks Figure 6-19 The RLC/MAC data blocks. Payload Payload Countdown MAC Header Value MAC Header TFI=51 BITS Spare TFI = 5 BITS BSN = 7 BITS BSN = 7 BITS Length Indicator Length Indicator Header Header Length Indicator Length Indicator RLC Data RLC Data Downlink RLC data block Uplink RLC data block MAC header contains the following: Uplink state flag (USF-3 bits) This is used to identify users for UL transmission, or to characterize a PRACH. Type (2 bits) The payload type that identifies the type of block that follows (RLC data block or RLC/MAC control block). Polling control (3 bits) One Supplementary/Polling (S/P) bit to poll the mobile station (so that it sends an acknowledgment message) and two RRBP bits to tell the mobile station where to send the acknowledgment message. The RLC data block's header contains the following: Block Sequence Number (BSN-7 bits) This carries the absolute BSN modulo 128 of each RLC data block within the TBF. Temporary Flow Identifier (TFI-5 bits) The TFI identifies the TBF to which the RLC block belongs. Power Reduction (PR-2 bits) This indicates the power level reduction of the next RLC blocks, which is based on GSM power control. Final Block Identifier (FBI-1 bit) The FBI indicates that the RLC data block is the last one of the downlink TBF (DL). 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. Radi