8 Radio Resource Functionality

03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS

8.1 Cell Selection and Reselection

An MS (in any mode of operation (A, B, or C)) cannot camp on more than one cell. If the MS is in idle mode, see GSM 03.22, then it shall use cell selection and reselection procedures as described in GSM 03.64 and specified in GSM 03.22 and GSM 05.08 [15].

8.2 Discontinuous Reception

A GPRS MS may be able to choose if it wants to use discontinuous reception (DRX) or not. If using DRX, the MS shall also be able to specify other DRX parameters that indicate the delay for the network to send a page request or a channel assignment to the MS (see GSM 03.64).

The DRX parameters shall be indicated by the MS in the attach procedure. The SGSN shall then in each page request send these parameters to the BSS that uses this information and the IMSI to calculate the correct paging group.

DRX usage is independent of the MM states IDLE, STANDBY and READY. As DRX can be used by a GPRS MS in READY state, DRX has to be considered also when assigning a packet data channel for downlink transfer. The SGSN shall therefore indicate the DRX parameters for the MS in all packet transmission requests to the BSS.

A GPRS MS shall not apply DRX in READY state during the GPRS attach and routeing area update procedures.

8.3 Radio Resource Management

GSM Radio Resource Management functions are defined in GSM 04.07 [10]. The radio interface layer 3 protocol is specified in GSM 04.08.

8.3.1 Layer Functions

GPRS radio resource management procedures are required for the following functions:

– allocation and release of physical resources (i.e., timeslots) associated with a GPRS channel;

– monitoring GPRS channel utilisation to detect under-utilised or congested GPRS channels;

– initiating congestion control procedures; and

– distribution of GPRS channel configuration information for broadcasting to the MSs.

8.3.2 Model of Operation

8.3.2.1 Dynamic Allocation of Radio Resources

A cell may or may not support GPRS.

A cell supporting GPRS may have GPRS radio resources allocated at a given instance. If no GPRS radio resources are allocated, an MS can request allocation of such resources. MSs may then use these radio resources. The PLMN may dynamically increase, to a PLMN operator-defined maximum, or, decrease to an operator-defined minimum, the radio resources allocated.

The network broadcasts GPRS system information on the common control channels.

GSM radio resources are dynamically shared between GPRS and other GSM services.

8.4 Paging for GPRS Downlink Transfer

An MS in STANDBY state is paged by the SGSN before a downlink transfer to that MS. The paging procedure shall move the MM state to READY to allow the SGSN to forward downlink data to the radio resource. Therefore, any uplink data from the MS that moves the MM context at the SGSN to READY state is a valid response to paging.

The SGSN supervises the paging procedure with a timer. If the SGSN receives no response from the MS to the Paging Request message, it shall repeat the paging. The repetition strategy is implementation dependent.

The MS shall accept pages also in READY state if no radio resource is assigned. This supports recovery from inconsistent MM states in MS and SGSN.

The GPRS Paging procedure is illustrated in Figure 33. Each step is explained in the following list.

Figure 33: GPRS Paging Procedure

1) The SGSN receives a downlink PDP PDU for an MS in STANDBY state. Downlink signalling to a STANDBY state MS initiates paging as well.

2) The SGSN sends a BSSGP Paging Request (IMSI, P‑TMSI, Area, Channel Needed, QoS, DRX Parameters) message to the BSS serving the MS. IMSI is needed by the BSS in order to calculate the MS paging group. P‑TMSI is the identifier by which the MS is paged. Area indicates the routeing area in which the MS is paged. Channel Needed indicates GPRS paging. QoS is the negotiated QoS for the PDP context that initiates the paging procedure, and indicates the priority of this Paging Request relative to other Paging Request messages buffered in the BSS. DRX Parameters indicates whether the MS uses discontinuous reception or not. If the MS uses discontinuous reception, then DRX Parameters also indicate when the MS is in a non-sleep mode able to receive paging requests.

3) The BSS pages the MS with one Paging Request (P‑TMSI, Channel Needed) message in each cell belonging to the addressed routeing area. This is described in GSM 03.64.

4) Upon receipt of a GPRS Paging Request message, the MS shall respond with either any single valid LLC frame (e.g., a Receive Ready or Information frame) that implicitly is interpreted as a page response message by the SGSN. When responding, the MS changes MM state to READY. The response is preceded by the Packet Channel Request and Packet Immediate Assignment procedures as described in GSM 03.64.

5) Upon reception of the LLC frame, the BSS adds the Cell Global Identity including the RAC and LAC of the cell and sends the LLC frame to the SGSN. The SGSN shall then consider the LLC frame to be an implicit paging response message and stop the paging response timer.