able to transmit on the UL. Hence, the mobile station may start data transmission on the allocated PDCH. Packet Uplink Assignment Several steps are involved when the mobile station needs access to enter packet transfer mode, as shown in Figure 6-14. One such example is the 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 PCUSN Figure 6-14 Packet Uplink Assignment message. Packet Channel bits, PRACH (or RACH) PAGCH (or AGCH) Packet Resource Request (2+1) PACCH Mandatory for PACCH 2 phase access Static or Bitmap allocation Dynamic or USF allocation Allocation bitmap downlink Control TS need to have an uplink time slot assigned SO that the mobile station can begin transferring data. The sequence uses the following dialogue: Access Request In order to result in a GPRS Attach Request, the mobile station sends a Packet Channel Request on the PRACH, which contains the following infor- mation: access type (one- or two-phase access) and some reference bits (ran- dom bits, priority bits). The Packet Channel Request could be found in two formats: 8 or 11 bits. Access Answer The network answers with a Packet Immediate Assignment message (which permits the allocation of a PACCH resource) sent on any PAGCH block on the same PCCCH. This message contains the single allocated block where the mobile station can make its request. 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 Resource Request When the mobile has received a Packet Immediate Assignment message, it can perform its request with a Packet Resource Request sent on the PACCH that has been allocated. This message contains the mobile