aded 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 allocated to carry packet logical channels. The packet (logical) channels are used in the uplink (UL) or downlink (DL) direction. Actually, unlike GSM, GPRS does not have a real duplex channel, except for the Packet Timing Advance Control Channel (PTCCH). The packet channels are classified in three families (the direction of flow is shown as UL, DL, or UL/DL). These are shown as the logical channels in Figure 6-2: The Packet Common Control Channels (PCCCH) are very similar in makeup to the Common Control Channel (CCCH). When not allocated in a cell, packet transfer can be initiated by the CCCH. The PCCCH is made up of several logical channel functions consisting of Packet Random Access Channel (PRACH UL) is used for random access. The PRACH is an uplink-only function used by the mobile station to initiate an uplink transfer for sending data or signaling information. The access burst used on the PRACH is also used to obtain any timing advance information. The mobile station to transmit the initial packet channel request uses the PRACH. It is the only request for short access or one-phase access. In the case of two- Figure 6-2 Logical Channels The logical channels assigned in GPRS. Common Channels Dedicated Channels Broadcast Common Common Channels Control Control Traffic Channels Channels Channels PBCCH PACCH PDTCH Broadcast Paging Notification Resource Assignment Traffic PRACH PAGCH PTCCH Random Access Timing Access Grant Advance 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 phase access, a second request follows (Packet Resourc