On top of the physical channels, a series of logical channels are defined to perform a multiplicity of functions, e.g., signalling, broadcast of general system information,synchronization, channel assignment, paging, or payload transport. Table below lists the packet data logical channels defined in GPRS. As with conventional GSM,they can be divided into two categories: traffic channels and signaling (control) channels.

The Packet Data Traffic Channel (PDTCH) is employed for transfer of user data. It is assigned to one MS (or in the case of PTM (point to Multipoint) to multiple mobile stations).

One mobile station can use several PDTCHs simultaneously.

The Packet Broadcast Control Channel (PBCCH) is a unidirectional point-to-multipoint signaling channel from the BSS to the MS. It is used by the BSS to broadcast specific information about the organization of the GPRS radio network to all GPRS mobile stations of a cell. Besides system information about GPRS, the PBCCH should also broadcast important system information about circuit switched services, so that a GSM/GPRS mobile station does not need to listen to the Broadcast Control Channel (BCCH).

The Packet Common Control Channel (PCCCH) is a bidirectional point-to multipoint signaling channel that transports signaling information for network access management,

e.g., for allocation of radio resources and paging. It consists of four sub-channels:

The Packet Common Control Channel (PCCCH) is used by the mobile to request one or more PDTCH.

The Packet Access Grant Channel (PAGCH) is used to allocate one or more PDTCH to a mobile station.

The Packet Paging Channel (PPCH) is used by the BSS to find out the location of a mobile station (paging) prior to downlink packet transmission.

The Packet Notification Channel (PNCH) is used to inform a mobile station of incoming PTM messages (multicast or group call).

The dedicated control channel is a bidirectional point-to-point signaling channel. It contains the channels PACCH and PTCCH :

The Packet Associated Control Channel (PACCH) is always allocated in combination with one or more PDTCH that are assigned to one mobile station. It transports Signaling information related to one specific mobile station (e.g., power control information).

The Packet Timing Advance Control Channel (PTCCH) is used for adaptive frame synchronization.

The coordination between circuit switched and packet switched logical channels is important. If the PCCCII is not available in a cell, a mobile station can use the Common Control Channel (CCCH) of conventional GSM to initiate the packet transfer. Moreover. if the PI3CCH is not available, it will listen to the Broadcast.

Control Channel (BCCH) to get informed about the radio network.

Figure above shows the principle of the uplink channel allocation (mobile originated packet transfer). A mobile station requests radio resources for uplink transfer by sending a "packet channel request" on the PRACH or RACH. The network answers on the PAGCH or AGCH, respectively. It tells the mobile station which PDCHs it may use.

A so-called Uplink State Flag (USF) is transmitted in the downlink to tell the mobile station whether or not the uplink channel is free.