8 Radio Resource Functionality

23.0603GPPGeneral Packet Radio Service (GPRS)Release 17Service descriptionStage 2TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.1 Radio Resource Functionality (A/Gb mode)

8.1.1 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 TS 23.122 [7b], it shall use cell selection and reselection procedures as described in TS 43.064 [11] and specified in TS 23.122 [7b] and TS 45.008 [16b].

8.1.2 Discontinuous Reception

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 [11]).

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.

8.1.2a Extended idle mode Discontinuous Reception (DRX)

8.1.2a.1 General

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 [119]. 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 [119]. 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.

NOTE: The extended idle mode DRX cycle length requested by UE takes into account requirements of applications running on the UE. Subscription based determination of eDRX cycle length can be used in those rare scenarios when applications on UE cannot be modified to request appropriate extended idle mode DRX cycle length. The network accepting extended DRX while providing an extended idle mode DRX cycle length value longer than the one requested by the UE, can adversely impact reachability requirements of applications running on the UE.

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 [119].

8.1.2a.2 Paging group occurrence determination in Gb mode

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 [78]. 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.

8.1.2a.3 Paging coordination between the MS and network in Iu mode

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 [119].

The MS monitors the network for paging messages during the Paging Transmission Window using its regular DRX parameters.

8.1.3 Radio Resource Management

A/Gb mode Radio Resource Management functions are defined in TS 24.007 [12]. The radio interface layer 3 protocol is specified in TS 24.008 [13].

8.1.3.1 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.

The radio resource management features that are required for PS handover are detailed in TS 43.129 [87].

8.1.3.2 Model of Operation

8.1.3.2.1 Dynamic Allocation of Radio Resources

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.

8.1.3a Ready to Standby state transition in S4 architecture

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.

Figure 55-5: READY to STANDBY transition within the network using S4

1. The READY timer expires in the SGSN.

2. If PDP Contexts associated are to be preserved:

– if ISR is activated for that MS, the SGSN shall send a Release Access Bearers Request to the S‑GW to remove the SGSN address for user plane and downlink S4 GTP-U TEID;

– if ISR is not activated for that MS, the SGSN may send a Release Access Bearers Request to the S‑GW to remove the SGSN address for user plane and downlink S4 GTP-U TEID.

3. If the S‑GW received a Release Access Bearers Request, the S‑GW returns a Release Access Bearers Response to SGSN.

8.1.4 Paging for GPRS Downlink Transfer (A/Gb mode)

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.

Figure 56: GPRS Paging Procedure (A/Gb mode)

NOTE: The procedure describes the flow when there is an established user plane between SGSN and GGSN with Gn/Gp based SGSN, or between SGSN and S‑GW with S4 based SGSN. In case of an S4 based SGSN, when the S‑GW has no downlink user plane TEIDs, procedure steps (A) and (B) are defined in clause 8.1.4A.

1) The SGSN receives a DL 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, 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.

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 TS 43.064 [11].

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. 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 [11].

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.

8.1.4A Paging response for GPRS Downlink Transfer with no established user plane on S4

Figure 56a: Paging with no established user plane on S4

Figure 56b: Paging Response with no established user plane on S4

NOTE: Steps A, B and E are common for architecture variants with GTP based S5/S8 and PMIP-based S5/S8. For a PMIP-based S5/S8, procedure steps (C) are defined in TS 23.402 [90]. Steps C and D concern GTP based S5/S8.

A) 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 5.3.6.5), 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.

B) 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.

C) If the RAT Type has changed compared to the last reported RAT Type, the S‑GW shall send the Modify Bearer Request message (RAT Type) to the PDN GW.

D) The PDN GW sends the Modify Bearer Response to the S‑GW.

E) The S‑GW sends a Modify Bearer Response to the SGSN.

8.1.5 RAN Information Management (RIM) procedures

8.1.5.1 General

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.

8.1.5.2 Addressing, routeing and relaying

8.1.5.2.1 Addressing

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.

8.1.5.2.2 Routeing

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.

8.1.5.2.3 Relaying

The SGSN performs relaying between BSSGP messages, RANAP messages and GTP messages as described in TS 48.018 [78], TS 25.413 [56b] and TS 29.060 [26].

8.1.5.3 Void

8.1.5.4 Void

8.1.5.5 Applications using the RIM Procedures

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 [78] and TS 25.413 [56b].

8.1.6 BSS Paging Co-ordination

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 6.3.3.1), 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.

8.2 Radio Resource Functionality (Iu mode)

8.2.1 Radio Resource Management

UTRAN functions are defined in TS 25.401 [53]. The radio interface protocol architecture is specified in TS 25.301 [50], and the Radio Resource Control protocol is specified in TS 25.331 [52]. TS 43.051 [74] contains an overall description of GSM/EDGE Radio Access Network.

In the context of this specification, the term URA refers also to GRA (GERAN Registration Area) when the RAN serving an MS in Iu mode is a GERAN.

8.2.2 RRC State Machine

The RRC state machine is a description model of how the MS and the Iu mode RAN co-operate regarding RRC functionality. The RRC state describes the MS state in the Iu mode RAN. This clause contains a brief description of the RRC state machine, for more information see TS 25.303 [51].

The RRC state machine exists as two peer entities, one in the MS and one in the Iu mode RAN. Apart from transient situations and error cases the two peer entities are synchronised. Figure 57 illustrates the main modes and states of the RRC state machine.

Figure 57: RRC Modes, Main RRC States and Main Mode and State Transition

RRC Idle mode: In the Idle mode there is no connection established between the MS and the Iu mode RAN. There is no signalling between RAN and the MS except for system information that is sent from RAN on a broadcast channel to the MS. The MS can also receive paging messages with a CN identity on the PCH. There is no information of the MS stored in RAN in this mode.

RRC Connected mode: In the Connected mode the main states are Cell Connected state and URA Connected state. In this mode there is one RNC/BSC that is acting as serving RNC/BSC, and an RRC connection is established between the MS and this SRNC/SBSC.

– When the MS position is known at the cell level, the MS is in the Cell Connected state. When in Cell Connected state, the RRC connection mobility is handled by handover and cell update procedures.

– When the MS position is known at the URA level, the MS is in the URA Connected state. URA updating procedures provide the mobility functionality in this state. No dedicated radio resources are used in the URA Connected state.

8.2.3 Discontinuous Reception

An MS can set the DRX cycle length that is specific to the PS domain. TS 25.304 [51b] describes how the MS shall select which DRX cycle length to use with respect to DRX cycle length requirements set by the RAN, CN PS domain and CN CS domain.

The DRX parameter information shall be indicated by the MS in the attach procedure and when changing from A/Gb mode to Iu mode also in the routeing area update procedure. The SGSN shall then in each page request send these parameters to the RNC/BSC that uses this information, and the IMSI, to calculate the correct paging group.

At inter SGSN change (either RA update or SRNS relocation), 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. There is one other exception to this: in order to support mobility from pre-Release 99 SGSNs, the MS shall include the DRX Parameter IE in a Routing Area Update Request message sent at RA update from GERAN to UTRAN.

At inter-SGSN RA update (e.g. from GERAN), if the network receives a DRX parameters IE from the MS in the routeing area update request message, the new SGSN shall use the information provided by the MS and shall ignore the same IE received in MM Context from the old SGSN.

If the UE wishes to alter its GERAN or UTRAN/E-UTRAN DRX Parameters while in Iu 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.

8.2.3a Extended idle mode Discontinuous Reception (DRX)

8.2.3a.1 General

In Iu mode, extended idle mode DRX may be enabled as described in clause 8.1.2a.1.

8.2.4 Paging Initiated by CN

A CN node requests paging only for MSs in CMM‑IDLE state or PMM‑IDLE state. In the separate CN architecture, paging from a CN node is done independently from the state of the MS in the other CN service domain.

In the context of this specification, the terms RNS or RNC refer also to a GERAN BSS or BSC (respectively) when serving an MS in Iu mode.

In this alternative with paging co-ordination in the RAN, the MS does not need to listen to the PCH (Paging Channel) in the RRC Connected mode, at least not when MS is allocated a dedicated channel.

For each paging request received from a CN node, the RNC determines whether the MS has an established RRC connection or not. In order to achieve this, the context that is prepared within the SRNC for MS in RRC Connected mode must contain the IMSI, which is the common MS identity for the two CN domains.

If no context is found for the MS, "normal PCH paging" is performed. The paging message is transferred on the paging channel, and it includes the MS paging identity received from the CN and a CN service domain type indication.

If a context is found, a "CN paging message" is transferred using the existing RRC connection. This message includes a CN service domain type indication. If, potentially after repetition, this transfer is unsuccessful and if the CS domain originally triggered the paging, the RNC should decide whether to attempt "normal PCH paging" as described in clause "Unsynchronous states in the UE and the UTRAN".

8.2.4.1 PS Paging Initiated by SGSN (Iu mode) without RRC Connection for CS

Figure 58: PS Paging by SGSN (Iu mode) Without RRC Connection for CS

NOTE 1: Steps 2‑4 are common for architecture variants using Gn/Gp based interaction with GGSN. For an S4 based interaction with S‑GW and P‑GW, procedure steps (A) are defined in clause 8.2.4.1A.

1) The 3G‑SGSN receives a DL PDU or downlink signalling for an MS in PMM Idle state.

2) The 3G‑SGSN sends a RANAP Paging (IMSI, P‑TMSI, Area, CN Domain Indicator, DRX parameters, list of CSG IDs for paging) message to each RNS belonging to the routeing area in which the MS is located. IMSI is needed by the RNS in order to calculate the MS paging group, and to identify the paged MS. If 3G‑SGSN assigned the P‑TMSI to the MS, P‑TMSI is also included. Area indicates the routeing area in which the MS is paged. CN Domain Indicator indicates which domain (MSC or 3G‑SGSN) initiated the paging message, and it represents "SGSN" in this case. DRX Parameters indicates the MS’s preferred DRX cycle length. The list of CSG IDs for paging is included when the 3G SGSN is configured to support paging optimisation described in clause 5.3.9. For paging optimisation, the CSG IDs of expired CSG subscriptions and valid CSG subscriptions are both included in the list. If the MS has emergency bearer service the 3G SGSN shall not perform paging optimization.

NOTE 2: An expired CSG subscription indicates that the MS is not allowed service in the CSG. However, since the removal of the CSG from the MS is pending, it is possible the MS will camp on that CSG and therefore the MS is still paged for the CSG.

3) The RNS controls whether the MS has an established RRC connection or not. In this case, MS has no RRC connection, so a "normal PCH paging" is performed. Paging Type 1(IMSI or P‑TMSI, Paging originator, CN domain ID) is transferred on the Paging channel, IMSI or P‑TMSI identifies the MS. Paging originator indicates whether this is core network originated paging or RAN originated paging, so it represents "CN" in this case. And CN domain ID indicates whether this paging message is for CS service or PS service, so it represents "PS" in this case.

4) The paging request triggers the Service Request procedures in the MS. The service request procedures are described in clause "Service Request Procedure (Iu mode)".

Optionally, 3G‑SGSN may include "Non Searching Indication" in RANAP Paging message in this case. If a "Non Searching Indication" parameter is present, the RNC will not search the established RRC connection, and just initiate "normal PCH paging".

8.2.4.1A Serving GW Triggered Paging (Iu mode) with S4

Figure 58a: Serving GW triggered paging with S4

A) If the S‑GW has no downlink user plane TEIDs for S4 and S12, the S‑GW buffers the DL PDUs 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 5.3.6.5), the S‑GW drops the downlink data packet. The steps below are not executed.

Otherwise the S‑GW sends a Downlink Data Notification to the SGSN.
If the S‑GW has downlink user plane TEIDs for S4 the DL PDUs are transferred to SGSN.

8.2.4.2 PS Paging Initiated by 3G‑SGSN With RRC Connection for CS

Figure 59: PS Paging by SGSN (Iu mode) With RRC Connection for CS

NOTE 1: Steps 2‑4 are common for architecture variants using Gn/Gp based interaction with GGSN and using S4 based interaction with S‑GW and P‑GW. For an S4 based interaction with S‑GW and P‑GW, procedure steps (A) are defined in clause 8.2.4.1A.

1) The 3G‑SGSN receives a DL PDU or downlink signalling for an MS in PMM Idle state.

2) The 3G‑SGSN sends a RANAP Paging (IMSI, P‑TMSI, Area, CN Domain Indicator, DRX parameters, list of CSG IDs for paging) message to each RNS belonging to the routeing area in which the MS is located. IMSI is needed by the RNS in order to calculate the MS paging group. If 3G‑SGSN assigned the P‑TMSI to the MS, P‑TMSI is included, and it identifies the MS is paged. Area indicates the routeing area in which the MS is paged. CN Domain Indicator indicates to which domain (MSC or 3G‑SGSN) the paging was initiated, and it represents "3G‑SGSN" in this case. DRX Parameters indicates whether or not the MS uses discontinuous reception and the DRX cycle length. The list of CSG IDs for paging is included when the 3G SGSN is configured to support paging optimisation described in clause 5.3.9. For paging optimisation, the CSG IDs of expired CSG subscriptions and valid CSG subscriptions are both included in the list. If the MS has emergency bearer service the 3G SGSN shall not perform paging optimization.

3) The RNS controls whether the MS has an established RRC connection or not. In this case, MS has an established RRC connection for CS service, so RNS sends an RRC Paging Type 2 (CN domain ID) message to the MS on established RRC connection. CN Domain ID indicates to which domain (CS or PS) the paging shall be directed, so it represents "PS" in this case.

4) The paging request triggers the Service Request procedures in the MS. The service request procedures are described in clause "Service Request Procedure (Iu mode)".

8.2.5 Paging Initiated by RAN

An MS in RRC URA/GRA connected state is paged by the RAN before a downlink transfer to that MS. The URA/GRA paging procedure shall move the RRC state to Cell Connected to allow the RAN to forward downlink data or signalling message to the radio resource. Therefore, the RRC: Cell Update message from the MS that moves the RRC State at the RAN to Cell Connected state is a valid response to URA/GRA paging.

The RAN supervises the paging procedure with a timer. If the RAN receives no response from the MS to the URA or GRA Paging Request message, it shall repeat the paging. The repetition strategy is implementation dependent. If it is unsuccessful and if the paging was originally triggered by the CS domain, it is the RNC’s responsibility to recover this situation by following the "normal PCH paging" mechanism (see clause "Paging Initiated by CN"). For more information see TS 25.303 [51].

The URA/GRA Paging procedure is illustrated in Figure 60.

Figure 60: URA/GRA Paging Procedure

1) The RAN receives a downlink PDP PDU for an MS in RRC URA/GRA connected state. Downlink signalling to an MS in RRC URA/GRA connected state initiates URA/GRA paging as well.

2) The RAN pages the MS with one Paging Type 1 (RNTI, Paging originator) message in each cell belonging to the URA/GRA where the MS exists. RNTI is the identifier by which the MS is paged. Paging originator indicates whether this is the core network originated paging or RAN originated paging, so it represents "RAN" in this case.

3) The paging request triggers the Cell Update procedures in the MS. The Cell Update procedures are described in TS 25.331 [52].