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 TS 23.122, it shall use cell selection and reselection procedures as described in TS 43.064 and specified in TS 23.122 and TS 45.008.
In A/Gb mode an MS may 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 TS 43.064).
The DRX parameters shall be indicated by the MS in the attach procedure. The SGSN shall then send these parameters in each page request 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. When a GPRS MS in READY state uses DRX, DRX has to be considered 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.
In A/Gb mode an MS shall not apply DRX in READY state during the GPRS attach and routeing area update procedures.
At inter SGSN change to an SGSN operating in A/Gb mode, the DRX parameters are sent from the old SGSN to the new SGSN as part of the MM context information. Hence, unless the DRX parameters have been altered, the UE should not include the DRX parameters in the Routing Area Update message sent to an A/Gb mode SGSN.
If the UE wishes to alter its GERAN or UTRAN/E-UTRAN DRX Parameters while in A/Gb mode, then it shall send a Routing Area Update Request message to the SGSN containing its new DRX Parameters. If ISR had been activated for the MS, then the MS shall deactivate ISR by setting its TIN to "P-TMSI" so that the MS performs a Tracking Area Update when it next enters E-UTRAN coverage. When the UE performs that Tracking Area Update, the MME will receive the updated DRX parameters within the MM context information sent by the old SGSN and hence the UE should not include them again in the Tracking Area Update.
In A/Gb and Iu mode an MS and the core network may negotiate the use of extended idle mode DRX as described in TS 23.682. If the MS decides to request for extended idle mode DRX, the MS includes an extended idle mode DRX parameters information element in the attach request and/or RAU request message. The MS shall also include the DRX parameters for regular idle mode DRX in attach request.
The SGSN decides whether to accept or reject the MS request for enabling extended idle mode DRX as described in TS 23.682. In case the SGSN accepts the extended idle mode DRX, the SGSN based on operator policies and, if available, the extended idle mode DRX cycle length value in the subscription data from the HLR/HSS, may also provide different values of the extended idle mode DRX parameters than what was requested by the MS. If the SGSN accepts the use of extended idle mode DRX, the MS shall apply extended idle mode DRX based on the received extended idle mode DRX parameters. If the MS does not receive the extended idle mode DRX parameters information element in the relevant accept message because the SGSN rejected its request or because the request was received by SGSN not supporting extended idle mode DRX, the MS shall apply its regular discontinuous reception.
When the MS has PDP context for emergency bearer services, the MS and SGSN follow regular discontinuous reception as defined in clause 8.1.2 / 8.2.3 and shall not use the extended idle mode DRX. Extended idle mode DRX parameters may be negotiated while the MS has PDP context for emergency bearer services. When the PDP context for emergency bearer services is deactivated, the MS and SGSN shall reuse the negotiated extended idle mode DRX parameters in the last RAU/Attach procedure.
The MS shall include the extended idle mode DRX parameters information element in each RAU message if it still wants to use extended idle mode DRX. At SGSN to SGSN, MME to SGSN and SGSN to MME mobility, the extended idle mode DRX parameters are not sent from the old CN node to the new CN node as part of the MM context information.
If the SGSN is requested to monitor Reachability for Data and the UE is about to become reachable for paging, the SGSN sends a Monitoring Report message to the address that was indicated in the related Monitoring Request as described in TS 23.682.
To determine the occurrence of ongoing paging group occurences for a given MS the SGSN uses the extended idle mode DRX parameters and a parameter called "time remaining until the next paging group occurence" received from the BSS for that MS see TS 48.018. If the SGSN needs to page the MS for which the SGSN has received the extended idle mode DRX parameters while the "time remaining until the next paging group occurence" parameter is not available, SGSN sends a paging message without concern for the next paging group occurrence. In that case BSS may respond to the SGSN with an indication that the paging message was not sent on the radio interface in which case the BSS includes the "time remaining until the next paging group occurence" parameter. The SGSN shall then reattempt the page taking the extended idle mode DRX parameters and the "time remaining until the next paging group occurence" parameter of the MS into consideration.
The value of the extended idle mode DRX cycle remains valid for the device (unless renegotiated) regardless of whether an SGSN actually triggers the transmission of a page to that device using any of the ongoing paging group occurences.
After reception of a BSS restart indication, the SGSN sends to the BSS a Dummy Paging message including a IMSI and the extended idle mode DRX parameters to the BSS. BSS will for this Dummy Page message calculate the "time remaining until the next paging group occurence" and reply back to the SGSN including the "time remaining until the next paging group occurrence" in a Dummy Paging response. SGSN will use that "time remaining until the next paging group occurence" information to adjust the paging timing for all MSs that are subject to extended Idle mode DRX.
The extended idle mode DRX parameters are valid until the next Attach/RAU procedure is conducted and comprise the extended Idle DRX cycle value and Paging Transmission Window.
The MS and the SGSN coordinate the start of the Paging Transmission Window as described in TS 23.682.
The MS monitors the network for paging messages during the Paging Transmission Window using its regular DRX parameters.
AnA/Gb mode 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.
A/Gb mode radio resources are dynamically shared between GPRS and CS domain services.
When idle mode packet buffering is performed in the S-GW, the SGSN needs to inform the S-GW each time that the MS changes from READY state to STANDBY state. The following figure illustrates the procedure between SGSN and S-GW.
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.
If extended idle mode DRX is negotiated between the MS and the CN paging requests are buffered in the SGSN until shortly before expiration of the device specific regular idle mode DRX cycle or extended idle mode DRX cycle (see clause 8.1.2a) or the device enters the Ready state. The SGSN sends paging requests to the set of BSSs managing the cells of interest (e.g. the cells in the routing area). The point when these paging requests are sent take into account the largest difference in radio interface synchronization between cells used for paging. More specifically, the set of cells within a routing area in which extended idle mode DRX is supported shall be time coordinated on the radio interface such that the largest difference in radio interface synchronization between any two cells in the set shall not exceed 4 seconds.
Upon receiving a paging request for a device that is subject to extended idle mode DRX the BSS calculates the precise paging opportunity on the radio interface using IMSI and the extended idle mode DRX value included within paging request. This calculation is performed independent of the number of CCCHs per cell.
If the MS included its capability of supporting restriction of use of Enhanced Coverage, the SGSN sends Enhanced Coverage Restricted parameter to the BSS in the Paging message.
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 the MS and the SGSN.
The GPRS Paging procedure in A/Gb mode is illustrated in Figure 56.
The SGSN sends a BSSGP Paging Request (IMSI, P-TMSI, Area, Channel Needed, QoS, DRX Parameters, Gb Coverage Class Information, cell associated with the Gb Coverage Class Information) 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, DRX Parameters in combination with the IMSI indicate when the MS is in a non-sleep mode able to receive paging requests. Gb Coverage Class Information, and the cell associated with the Gb Coverage Class Information may be used by BSS to optimize the radio paging procedure.
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. The MS shall not use the LLC NULL frame as a page response. When responding, the MS changes MM state to READY. The Packet Channel Request precedes the response and Packet Immediate Assignment procedures as described in TS 43.064.
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.
When the S-GW receives a downlink PDU and no downlink user plane exists for the UE at S4, the S-GW buffers the downlink data packet and identifies which SGSN is serving that UE.
If that SGSN has requested the S-GW to throttle downlink low priority traffic and if the downlink data packet is received on a low priority bearer to be throttled (see clause 220.127.116.11), the SGW drops the downlink data packet. The steps below are not executed.
Otherwise the S-GW sends a Downlink Data Notification message to the SGSN.
Steps between A and B are described in clause 8.1.4.
Upon reception of the LLC frame in STANDBY state and if the user plane tunnel does not exist, the SGSN shall indicate the paging response from GERAN by sending a Modify Bearer Request (SGSN user plane address, RAT Type, TEID) to the Serving GW. The S-GW is now able to transmit downlink data towards the UE.
The RAN Information Management (RIM) procedures provide a generic mechanism for the exchange of arbitrary information between applications belonging to the RAN nodes. The RAN information is transferred via the SGSN core network node(s). In order to make the RAN information transparent for the Core Network, the RAN information is included in a RIM container that shall not be interpreted by the Core Network nodes.
The RIM procedures are optional both in the RAN node and in the SGSN. For the Gb interface the use of RIM procedures is negotiated at start/restart of the Gb link. For the Iu interface there is no negotiation of using RIM procedures or not at Iu link start/restart.
The RAN information is transferred in RIM containers from the source RAN node to the destination RAN node by use of messages. Each message carrying the RIM container is routed and relayed independently by the SGSN(s). Any relation between messages is transparent for the SGSN, i.e. a request/response exchange between RIM applications, for example, is routed and relayed as two independent messages by the SGSN.
The interfaces which will be used are the Gb (BSSGP) , the Iu (RANAP), the Gn (GTPv1) and the S16 (GTPv2) interfaces. The RAN information in the RIM container shall be transparent for the Core Network. An SGSN supporting the RIM procedures provides addressing, routeing and relay functions.
All the messages used for the exchange of RAN information contain the addresses of the source and destination RAN nodes. A BSS is addressed by Routeing Area Identity (RAI) + Cell Identity (CI) of one of its cells. An RNC is addressed by Global RNC-Id.
The following description applies to all the messages used for the exchange of RAN information.
The source RAN node sends a message to its SGSN including the source and destination addresses. An RNC sends in addition a RIM routing address, which is a copy of the destination address. From the destination address or from the RIM routing address, the SGSN shall decide whether or not it is connected to the destination RAN node.
If the SGSN is not connected to the destination RAN node, then it shall use the destination address or the RIM routing address to route the message encapsulated in a GTP message to the correct SGSN via the Gn interface. If the destination address or RIM routing address identifies an RNC the SGSN includes the RIM routing address in the GTP message. If the SGSN received the message from a BSC it copies the destination address from the message into the RIM routing address.
The SGSN connected to the destination RAN node decides which RAN node to send the message to based on the destination address or on the RIM routing address.
The RAN node applications, which use the RIM procedures, are fully transparent for the SGSN. These applications are described in RAN specifications. An example is the Network Assisted Cell Change described in TS 48.018 and TS 25.413.
In Network Operation Mode II, paging from one CN domain is done independently from the state of the MS in the other CN domain, i.e. no paging co-ordination on core network level is done.
It is, however, possible to do paging co-ordination on BSS level in these cases. This means that for each paging request received from one CN domain, the BSC determines whether the MS is engaged with the other CN domain or not. In order to achieve this, the context that is prepared within the BSC for an MS engaged with one of the CN domains must contain the IMSI, which is the common MS identity for the two CN domains.
If the BSC determines that the MS is engaged with the PS domain, the CS paging will be done on a packet data channel for the MS in question.
If the BSC determines that the MS is engaged with the CS domain, the PS paging (packet notification) will be done on a CS dedicated channel for the MS in question.
If no context is found for the MS, "normal CS paging" is performed on the CCCH paging channel and "normal PS paging" is performed on the CCCH paging channel or the packet paging channel (PCCCH shall not be used, see clause 18.104.22.168), as applicable.
If BSS paging co-ordination for CS paging is active in a cell or not, shall be indicated as system information to the MSs. For proper operation, the mode should be the same in each cell of a routeing area.
BSS paging co-ordination for PS paging shall always be active in a cell where DTM is supported and is applicable to MSs supporting DTM.