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Content for  TS 23.060  Word version:  16.0.0

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6.12  Service Request Procedure (Iu mode)

6.12.0  General |R8|

The Service Request procedure is used by a 3G MS in PMM IDLE state to request the establishment of a secure connection to a 3G SGSN. The MS in PMM IDLE state initiates this procedure in order to send uplink signalling messages (e.g. Activate PDP Context Request), user data, or as paging response, or after the MS has regained UTRAN (or Iu mode GERAN) radio coverage. This procedure is also used by an MS in PMM CONNECTED state to request resource reservation for active PDP contexts.
In the context of this specification, the terms RNC refer also to a GERAN BSC when serving an MS in Iu mode.
TS 23.401, clause 5.3.4.3) includes the description of the network initiated Service Request procedure using S4.
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6.12.1  MS Initiated Service Request Procedure Using Gn/GpWord‑p. 175
The MS in PMM IDLE state sends the Service Request message to the 3G SGSN in order to establish the PS signalling connection for the upper layer signalling or for the resource reservation for active PDP context(s). After receiving the Service Request message, the 3G SGSN may perform authentication, and it shall perform the security mode procedure. After the establishment of the secure PS signalling connection to a 3G SGSN, the MS may send signalling messages, e.g. Activate PDP Context Request, to the 3G SGSN, or the 3G SGSN may start the resource reservation for the active PDP contexts depending on the requested service in the Service Request message. An MS in PMM CONNECTED state also requests the resource reservation for the active PDP contexts through this procedure. An MS in PMM CONNECTED state also requests the resource reservation for preserved active PDP contexts that need to transfer data but have not been allocated resources in a previous Service Request.
Reproduction of 3GPP TS 23.060, Figure 50: MS Initiated Service Request Procedure using Gn/Gp
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Step 1.
The MS establishes an RRC connection, if none exists for CS traffic.
The MS shall signal a cause that indicates emergency when it requests an RRC connection for PS emergency services, as defined in TS 25.331.
Step 2.
The MS sends a Service Request (P-TMSI, RAI, CKSN, Service Type) message to the SGSN. Service Type specifies the requested service. Service Type shall indicate one of the following: Data or Signalling. When the Service Type indicates Data, the UE may also include PDP context activity information to indicate which PDP contexts need to transfer data. At this point, the SGSN may perform the authentication procedure.
If Service Type indicates Data, a signalling connection is established between the MS and the SGSN, and resources for active PDP context(s) are allocated, i.e. RAB establishment for the activated PDP context(s).
If Service Type indicates Signalling, the signalling connection is established between the MS and the SGSN for sending upper-layer signalling messages, e.g. Activate PDP Context Request. The resources for active PDP context(s) are not allocated.
CSG ID is provided if the MS sends the Service Request message via a CSG cell or hybrid cell. CSG access mode is provided if the MS sends the Service Request message via a hybrid cell. If the CSG access mode is not provided but the CSG ID is provided, the SGSN shall consider the cell as a CSG cell.
If a CSG ID is indicated and CSG access mode is "closed" or CSG access mode is not provided, and there is no subscription data for this CSG ID and associated PLMN or the CSG subscription is expired, the SGSN rejects the Service Request with an appropriate cause. The UE shall remove the CSG ID and associated PLMN of the cell where the UE has initiated the service request procedure from the Allowed CSG list, if present.
For MSs with emergency PDP contexts, i.e. at least one PDP Context has an ARP value reserved for emergency services, and if CSG access restrictions do not allow the MS to get normal services, the SGSN shall deactivate all non-emergency PDP contexts and accept the Service Request.
If LIPA is active for a PDP context and if the cell accessed by the MS does not link to the L-GW where the MS initiated the LIPA PDP context, the SGSN shall not request the establishment of the bearers of the LIPA PDP context from the RNC in step 4 and shall disconnect the LIPA PDP context by means of the SGSN-initiated PDP Context Deactivation Procedure according to clause 9.2.4.2.
Step 3.
The SGSN shall perform the security functions if the MS in PMM-IDLE state initiated the service request.
Step 4.
If the network is in PMM-CONNECTED state and the Service Type indicates Data, the SGSN shall respond with a Service Accept message towards the MS, in case the service request can be accepted. In case Service Type indicates Data, the SGSN sends a Radio Access Bearer Assignment Request (NSAPIRAB ID(s), TEID(s), QoS Profile(s), SGSN IP Address(es), UE-AMBR, CSG Membership Indication, MSISDN, APN, Charging characteristics) message to re-establish radio access bearers for PDP contexts which do not have maximum bit rates for uplink and downlink of 0 kbit/s. If Direct Tunnel is established the SGSN provides to the RNC the GGSN's User Plane Address(es) and TEID(s) for uplink data instead of the SGSN's IP Address(es) and TEID(s). The SGSN may in addition use PDP context activity information provided by the UE in the Service Request to decide which RABs to set up. MSISDN, APN and Charging characteristics are optional parameters and only transferred if SGSN supports SIPTO at Iu-ps. For RABs belonging to a PDP context/PDN connection for Local IP Access or SIPTO at the Local Network with L-GW function collocated with the HNB, the RAB Assignment Request message includes a Correlation ID for enabling the direct user plane path between the HNB and the L GW. For RABs belonging to a PDP context/PDN connection for SIPTO at the Local Network with L-GW function collocated with the HNB, the RAB Assignment Request message includes a SIPTO Correlation ID for enabling the direct user plane path between the HNB and the L-GW.
If the Service Request is performed via a hybrid cell, the CSG Membership Indication indicating whether the UE is a CSG member shall be included. Based on this information, the RAN can perform differentiated treatment for CSG and non-CSG members.
If the MS is not allowed to access the cell where the MS initiated the service request due to CSG access restriction, the SGSN shall only request to establish radio access bearers for Emergency PDP contexts.
Step 5.
The RNC indicates to the MS the new Radio Bearer Identity established and the corresponding RAB ID with the RRC radio bearer setup procedure.
Step 6.
SRNC responds with the Radio Access Bearer Assignment Response (RAB ID(s), TEID(s), QoS Profile(s), RNC IP Address(es)) message. The GTP tunnel(s) are established on the Iu interface.
Step 7.
If the RNC returns a Radio Access Bearer Assignment Response message with a cause indicating that the requested QoS profile(s) can not be provided, e.g. "Requested Maximum Bit Rate not Available", the SGSN may send a new Radio Access Bearer Assignment Request message with different QoS profile(s). The number of re-attempts, if any, as well as how the new QoS profile(s) values are determined is implementation dependent. For each RAB re-established with a modified QoS profile, the SGSN initiates a PDP Context Modification procedure to inform the MS and the GGSN of the new negotiated QoS profile for the corresponding PDP context. If the SGSN established Direct Tunnel in step 4) it shall initiate a PDP Context Modification procedure to the GGSN and provide to the GGSN the RNC's Address for User Plane and TEID for Downlink data and shall include the DTI to instruct the GGSN to apply Direct Tunnel specific error handling procedure as described in clause 13.8. If the internal flag Pending Network Initiated PDN Connection Signalling is set, the SGSN indicates MS available for end to end signalling in the PDP Context Modification procedure to the GGSN and reset the flag.
If SIPTO at the local network is active for a PDP context and for stand alone GW case, the Local Home Network ID is not the same as where the UE initiated the SIPTO at the local network PDN Connection, the SGSN shall request disconnection of the SIPTO at the Local network PDN connection(s) with the "reactivation requested" cause value according to clause 9.2.4.2.
If SIPTO at the local network is active for a PDP context and collocated L-GW case, the L-GW CN address of the cell accessed by the UE differs from the L-GW CN address of the cell where the UE initiated the SIPTO at the Local Network PDN Connection, the SGSN shall request disconnection of the SIPTO at the Local network PDN connection(s) with the "reactivation requested" cause value according to clause 9.2.4.2.
Step 8.
The MS sends the uplink packet.
For Service Type = Signalling, the MS knows that the Service Request message was successfully received in the SGSN when the MS receives the RRC Security Mode Control Command message.
For Service Type = Data, in PMM-IDLE, the MS knows that the Service Request was successfully received when the MS receives the RRC Security Mode Control Command message from the RNC; in PMM-CONNECTED state, the MS knows that the Service Request was successfully received when the MS receives the Service Accept message.
For any Service Type, in case the service request cannot be accepted, the network returns a Service Reject message to the MS with an appropriate cause value.
For Service Type = Data, in case the SGSN fails to re-establish RAB(s) for the PDP context(s), the SGSN determines if an SM procedure, such as SGSN-Initiated PDP Context Modification or PDP Context Deactivation, should be initiated. The appropriate action depends on the QoS profile of the PDP context and is an operator choice.
For each PDP context using streaming or conversational traffic class with maximum bit rate for uplink and downlink of 0 kbit/s the MS starts the MS-Initiated PDP Context Modification procedure or the MS-Initiated PDP Context Deactivation procedure to inform the SGSN whether to re-activate or to delete the PDP contexts. If the PDP context has been deactivated locally in the MS, the MS shall not perform the PDP context deactivation procedure for this PDP context because the list of active and inactive PDP contexts is included in the Service Request Message sent prior to the network.
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6.12.1A  UE Initiated Service Request Procedure Using S4 |R8|Word‑p. 177
The procedures described in figure 50a shows only the steps, which are different from the Gn/Gp variant of the procedure described in clause 6.12.1. due to the use of S4.
Reproduction of 3GPP TS 23.060, Figure 50a: UE Initiated Service Request Procedure using S4
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A)
If the RNC returns a Radio Access Bearer Assignment Response message with a cause indicating that the requested QoS profile(s) can not be provided, e.g. "Requested Maximum Bit Rate not Available", the SGSN does not send any new Radio Access Bearer Assignment Request message with different QoS profile(s), the RAB is not established. For each established RABs, the SGSN sends Modify Bearer Request messages to the Serving GW (Downlink S4/S12 TEID). If the S-GW receives a DL packet for an unaccepted bearer, the S-GW drops the DL packet and does not send a Downlink Data Notification to the MME. For the established RABs, if the SGSN established Direct Tunnel it includes the RNC's Address for User Plane TEID for downlink data and DTI. If Direct Tunnel is not used, the SGSN includes SGSN Address for User Plane and TEID for downlink data. The Serving GW is now able to transmit downlink data towards the UE. If there is no Direct Tunnel the SGSN sends downlink packet. If the internal flag Pending Network Initiated PDN Connection Signalling is set, the SGSN indicates MS available for end to end signalling in the PDP Context Modification procedure to the GGSN and reset the flag.
If any EPS bearers are to be released the SGSN triggers the bearer release procedure as specified in clause 9.2.4.2.
B)
If the RAT Type has changed compared to the last reported RAT Type and/or the indication MS available for end to end signalling is present, the Serving GW shall send the Modify Bearer Request message (RAT Type) to the PDN GW. The PDN GW sends the Modify Bearer Response to the Serving GW. The indication MS available for end to end signalling is also included if the indication was present in step A.
C)
The Serving GW acknowledges by sending Modify Bearer Response (SGW address for user plane and uplink S4 GTP-U TEID) to the SGSN.
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6.12.2  Network Initiated Service Request Procedure using Gn/GpWord‑p. 178
When the 3G SGSN receives a downlink packet (e.g. Request PDP Context Activation, Mobile-terminated SMS, user data) for an MS in PMM IDLE state, the 3G SGSN sends a paging request to RAN. The paging request triggers the Service Request procedure in the MS.
Reproduction of 3GPP TS 23.060, Figure 51: Network Initiated Service Request Procedure
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If a LIPA or SIPTO at the local network with L-GW function collocated with the HNB PDP context exists, when the L-GW receives the downlink data for an MS in PMM-IDLE state, the L GW sends the first downlink user packet to the SGSN and buffers all other downlink user packets. When S4 is used, the L-GW sends the first downlink user packet to Serving GW and the Serving GW will trigger the SGSN to page the UE.
Step 1.
The SGSN receives a downlink PDP PDU for an MS in PMM IDLE state.
A Gn/Gp-SGSN that detects that the MS is in a power saving state (e.g. Power Saving Mode or extended idle mode DRX) and cannot be reached by paging at the moment, shall invoke extended buffering depending on operator configuration, except for cases described in next paragraphs. The Gn/Gp-SGSN derives the expected time before radio bearers can be established to the MS (Iu case) or the MS can be reached (Gb case) and uses this as the buffer time. The Gn/Gp-SGSN stores the buffer time as a new value for the DL Data Buffer Expiration Time in the MM context for the MS and skips the remaining steps of this procedure. The DL Data Buffer Expiration Time is used for MSs using power saving state and indicates that there are buffered data in the Gn/Gp-SGSN and that the user plane setup procedure is needed when the MS makes signalling with the network.
The SGSN may use additional information based on a SLA with the MTC user for when to invoke extended buffering, e.g. only invoke it for a certain APN, do not invoke it for certain subscribers, etc.
Step 2.
The SGSN sends a Paging message to the RNC. The RNC pages the MS by sending a Paging message to the MS. See clause "Paging Initiated by CN" for details.
Step 3.
The MS establishes an RRC connection if none exists for CS traffic.
Step 4.
The MS sends a Service Request (P-TMSI, RAI, CKSN, Service Type) message to the SGSN. Service Type specifies Paging Response. The Service Request is carried over the radio in an RRC Direct Transfer message and over the Iu interface in the RANAP Initial MS message. At this point, the SGSN may perform the authentication procedure. The SGSN knows whether the downlink packet requires RAB establishment (e.g. downlink PDU) or not (e.g. Request PDP Context Activation or Mobile-terminated SMS).
CSG ID is provided if the MS attaches via a CSG cell or hybrid cell. CSG access mode is provided if the MS sends the Service Request message via a hybrid cell. If the CSG access mode is not provided but the CSG ID is provided, the SGSN shall consider the cell as a CSG cell.
If a CSG ID is indicated and CSG access mode is "closed" or CSG access mode is not provided, and there is no subscription data for this CSG ID and associated PLMN or the CSG subscription is expired, the SGSN rejects the Service Request with an appropriate cause. The MS shall remove the CSG ID and associated PLMN of the cell where the MS has initiated the service request procedure from the Allowed CSG list, if present.
For MSs with emergency PDP contexts, i.e. at least one PDP Context has an ARP value reserved for emergency services, and if CSG access restrictions do not allow the MS to get normal services, the SGSN shall deactivate all non-emergency PDP contexts and accept the Service Request.
Step 5.
The SGSN shall perform the security mode procedure.
Step 6.
If resources for the PDP contexts are re-established, the SGSN sends a Radio Access Bearer Assignment Request (RAB ID(s), TEID(s), QoS Profile(s), SGSN IP Address(es), UE-AMBR, CSG Membership Indication, MSISDN, APN, Charging characteristics) message to the RNC. If Direct Tunnel is established the SGSN provides to the RNC the GGSN's User Plane Address and TEID for uplink data. The RNC sends a Radio Bearer Setup (RAB ID(s)) to the MS. The MS responds by returning a Radio Bearer Setup Complete message to the RNC. The RNC sends a Radio Access Bearer Assignment Response (RAB ID(s), TEID(s), RNC IP Address(es)) message to the SGSN in order to indicate that GTP tunnels are established on the Iu interface and radio access bearers are established between the RNC and the MS. If the RNC returns a Radio Access Bearer Assignment Response message with a cause indicating that the requested QoS profile(s) can not be provided, e.g. "Requested Maximum Bit Rate not Available", the SGSN may send a new Radio Access Bearer Assignment Request message with different QoS profile(s). The number of re-attempts, if any, as well as how the new QoS profile(s) values are determined is implementation dependent. MSISDN, APN and Charging characteristics are optional parameters and only transferred if SGSN supports SIPTO at Iu-ps. For RABs belonging to a PDP context/PDN connection for Local IP Access or SIPTO at the Local Network with L-GW function collocated with the HNB, the RAB Assignment Request message includes a Correlation ID for enabling the direct user plane path between the HNB and the L-GW. For RABs belonging to a PDP context/PDN connection for SIPTO at the Local Network with L-GW function collocated with the HNB, the RAB Assignment Request message includes a SIPTO Correlation ID for enabling the direct user plane path between the HNB and the L-GW.
If the Service Request is performed via a hybrid cell, the CSG Membership Indication indicating whether the UE is a CSG member shall be included. Based on this information the RAN can perform differentiated treatment for CSG and non-CSG members.
If the MS is not allowed to access the cell where the MS initiated the service request due to CSG access restriction, the SGSN shall only request to establish radio access bearers for Emergency PDP contexts.
Step 7.
For each RAB re-established with a modified QoS profile, the SGSN initiates a PDP Context Modification procedure to inform the MS and the GGSN of the new negotiated QoS profile for the corresponding PDP context. If SGSN established Direct Tunnel in step 6) it shall initiate a PDP Context Update procedure to the GGSN and provide to the GGSN the RNC's Address for User Plane and TEID for Downlink data and shall include the DTI to instruct the GGSN to apply Direct Tunnel specific error handling procedure as described in clause 13.8.
Step 8.
The SGSN sends the downlink packet. For a LIPA or SIPTO at the Local Network with L-GW function collocated with the HNB PDP context, after the MS enters connected mode, the packets buffered in the L-GW are forwarded to the HNB on the direct path. If the MS enters connected mode at a different cell than the one where the L-GW is collocated, for LIPA PDP context the SGSN shall deactivate the LIPA PDP context as defined in clause 6.12.1, step 2, for SIPTO at the Local network with L-GW function collocated with the HNB the SGSN shall trigger the L-GW reallocation as defined in clause 6.12.1 step 7.
For Service Type = Page Response, the MS knows that the Service Request message was successfully received in the SGSN when the MS receives the RRC Security Mode Control Command message.
If the SGSN fails to re-establish RAB(s) for the PDP context(s), the SGSN determines if an SM procedure, such as SGSN-Initiated PDP Context Modification or PDP Context Deactivation, should be initiated. The appropriate action depends on the QoS profile of the PDP context and is an operator choice.
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6.12.2AVoid


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