A.2 Selection Rules

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

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

The SGSN shall select the APN to be used to derive the GGSN or P-GW address, and set the selection mode parameter according to the rules in the SDL diagrams in this clause. The following definitions apply to the SDL diagrams:

AddrMode: Addressing Mode, temporary parameter set in the selection process to either of:

AddrMode := static

AddrMode := dynamic

APN‑OI: APN Operator Identifier.

HPLMN AP: HPLMN Access Point.

HPLMN OI-1: HPLMN APN Operator Identifier type 1 (derived from the APN OI Replacement field in the subscriber’s profile).

HPLMN‑OI-2: HPLMN APN Operator Identifier type 2 (derived from IMSI).

Number <condition>: determines the PDP context subscription records that satisfy the given condition.

ODB parameter: Operator Determined Barring parameter configured in subscriber data to one of:

All Packet Oriented Services barred

Roamer Access to HPLMN-AP barred

Roamer Access to VPLMN-AP barred

PDPaddr: PDP address.

SelMode: APN selection mode, temporary parameter set in the selection process to either of:

SelMode := ChosenBySGSN: Network-provided APN, subscription not verified.

SelMode := SentByMS: MS-provided APN, subscription not verified.

SelMode := Subscribed: MS or Network-provided APN, subscription verified.

VPLMN AP: VPLMN Access Point.

VPLMN‑OI: VPLMN APN Operator Identifier or the APN Operator Identifier of an associated PLMN when the VPLMN is a shared network.

PDN GW allocation type: PDN GW allocation type is not for the GGSN selection but only for the PDN GW selection. It is either static or dynamic.

Static: for the determined APN, the selected PDN GW has been statically allocated.

Dynamic: for the determined APN, the selected PDN GW can be dynamically allocated.

+: concatenation operation.

The subscription data may contain the information whether SIPTO is allowed or prohibited for each subscribed APN or the SGSN may know from configuration whether SIPTO is allowed or prohibited for a given APN. An indication that SIPTO is allowed or prohibited for the wild card APN allows or prohibits SIPTO for any APN that is not present in the subscription data. When a PDP context for SIPTO is established, the SGSN uses either the RAI (Routing Area Identity) and/or the serving RNC identifier depending on the operator’s configuration during the DNS interrogation as specified in TS 29.303 [100]. In roaming scenario the GW selection for a PDP context with SIPTO is only possible when a GGSN or a P-GW in the visited PLMN is selected. Therefore in a roaming scenario with home routed traffic, GW selection for SIPTO is not performed. When the UE is in a network with A/Gb mode and SIPTO is allowed for the given APN, the RAI may also be used for PGW/GGSN selection. In this way when the UE enters UTRAN or E-UTRAN the PDP context deactivation with reactivation request to find an optimal PGW/GGSN for SIPTO may not be needed.

The subscription data may also contain the information on whether:

a) an APN is LIPA-conditional, LIPA-prohibited, or LIPA-only;

b) a CSG in the UE’s CSG subscription data supports APN(s) that are LIPA-only or LIPA-conditional; and

c) LIPA is allowed in a list of VPLMNs when roaming.

When a PDP context for a LIPA APN is established, the SGSN uses the L-GW address included by HNB in RANAP messages as the GGSN/PGW address to be used, instead of DNS interrogation for GGSN/PGW selection. If no collocated L-GW address is included by the HNB and the UE requested a LIPA only APN, the request shall be rejected. If no collocated L-GW address is included by the HNB and the UE requested a LIPA conditional APN, the SGSN uses DNS interrogation for GGSN/PGW selection to establish a non-LIPA PDP context. The subscription data for an APN with LIPA permissions set to "LIPA-only" shall not contain a statically configured PDP address or a statically allocated PDN GW. A static PDP address or a static PDN GW address, if configured by HSS for an APN with LIPA permissions set to "LIPA-conditional", is ignored by SGSN when the APN is established as a LIPA PDP context. When establishing a PDP context for a LIPA APN, the VPLMN Address Allowed flag is not considered.

In the procedure denoted "Interface and protocol selection" in Figure A.8, the SGSN shall select one of the configurations listed in Table A.1.

The SGSN may use the UE capability (indicated as part of the MS Network Capability) and roaming agreement as indicated in clause 5.3.7.1 as input to select between configurations using GGSN or P-GW as well as the interface type (Gp or S4/S8). The SGSN may give priority for a configuration using P-GW for E-UTRAN capable UEs, and GGSN for non E-UTRAN capable UE.

If the SGSN supports Gn/Gp only, selection between the configurations indexed 1 and 2 are applicable. If the SGSN supports both Gn/Gp and S4, any of the configurations in Table A.1 apply. In case of P-GW selection, the service parameter shall be set as given in the respective column of Table A.1 and applied as defined in TS 29.303 [100].

If the HLR/HSS provides a subscription context that allows for allocation of a GGSN/PGW from the visited PLMN for this APN and, optionally, the SGSN is configured to know that the visited VPLMN has a suitable roaming agreement with the HPLMN of the UE, the GGSN/PGW selection function derives a GGSN/PGW from the VPLMN. If a visited GGSN/PGW cannot be derived, the APN is used to derive a GGSN/PGW from the HPLMN.

DNS interrogation in Figure A.8 shall be performed based on the full APN (APN-NI +APN-OI). For index of 2, 3, or 4 DNS interrogation procedure is defined by TS 29.303 [100]. For index 1 the DNS interrogation is a DNS A query and/or DNS AAAA query at the full APN exactly as in pre-Release 8 networks. Fall back to the legacy procedure (i.e. index 1) is required for indexes 2, 3, and 4 if they fail since the APN may represent a pre-Release 8 network.

Table A.1: Gateway interface and protocol configurations

Index	Gateway node	Interface type	Protocol on S5/S8	Service parameter
1	GGSN	Gn/Gp	n.a.	no
2	P-GW	Gn/Gp	n.a.	yes
3	P-GW	S4	GTPv2	yes
4	P-GW	S4	PMIP	yes

Figure A.1: APN selection-Null Parameter present

Figure A.2: APN selection-PDPtype(R) present

Figure A.3: APN selection- APN(R) not present or PDPaddr(R) present

Figure A.4: LIPA authorization

Figure A.5: APN PLMN selection-APN from subscription or MS

Figure A.6: APN PLMN selection-APN chosen by SGSN

NOTE: This process is only applied by an SGSN when S4 is used.

Figure A.7: APN selection-Dynamic stored PGW selection

Figure A.8: APN DNS query

Annex B (informative):
Selected IP Traffic Offload at Iu-PS