o and MS-PCUSN Interfaces Chapter 6 Length indicators (optional bytes) Length delimits the LLC frames when an RLC block contains more than one LLC frame. Temporary Logical Link Identifier (TLLI-several bytes) This identifier identifies the logical link established between the user and the Serving GPRS Support Node (SGSN) (UL only). Temporary Block Flow-Uplink (UL) Data Transfer This procedure, shown in Figure 6-20, is an example of message sequence for the uplink data transfer with one resource reallocation and possible RLC data blocks retransmissions (we assume that the transfer mode is ACK). A contention resolution mechanism is adopted in order to avoid two mobile stations perceiving the same UL channel as their own. If static allo- cation is used, this mechanism is the UL bitmap transmission for the allocated UL PDCH, and if dynamic allocation is used, the USF field trans- mitted on the DL radio blocks dynamically indicates the attribution of the next UL radio block. Figure 6-20 BSC PCUSN The uplink data Network transfer. Network Data Block PDTCH Data Block PDTCH Data Block PDTCH Data Block (last in send window) PDTCH Temporary Packet Ack/Nack PACCH Data Block PDTCH Data Block PDTCH Data Block PDTCH Packet Resource Reassignment PACCH Packet Resource Reassignment Ack PACCH Data Block PDTCH Data Block (last) PDTCH Final Packet Ack/Nack PACCH 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 Two modes of transmission are available: acknowledged and unac- knowledged. The mode of transmission is indicated in the PDP context acti- vation (quality of service [QoS] field). In the acknowledged mode of DL transmission, the mobile station is reg- ularly polled through the S/P bit in the MAC header, and it should transmit an acknowledgment bitmap in the correct block indicated in the RRBP fiel