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Interfaces
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==========
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See also: LTE-Multi-RAT 2.1.3
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5
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6
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Rel.7 SGSN:
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7
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Gn: SGSN<->PDN-GW (GTPv1C, 3gpp ts 29.060)
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8
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-> 3gpp ts 3gpp TS 29.060, section 7.5.14 RAN Information Management Messages (RIM)
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9
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Procedures: 3gpp TS 23.060, section 8.1.5, Messages: 3gpp TS 48.018
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Gn: SGSN<->MME
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Gr: SGSN<->HSS/HLR
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12
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13
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Rel.8 SGSN:
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14
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S4: SGSN<->SGW (GTPv2-C)
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15
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S3: SGSN<->MME
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S6d: SGSN<->HSS/HLR (Diameter)
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17
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Direct tunneling (3G)
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S12: SGW<->RNC (GTPv1-U)
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Interfaces using RIM: Gb (BSSGP), Iu (RANAP), Gn (GTPv1), S16 (GTPv2) Routing
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====================
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= PS HO =
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====================
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Cell Reselection from GRPS (Packet transfer mode or packet_idle) to E-UTRA (RRC idle)
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Cell Reselection from E-UTRA (any state) to GERAN (packet_idle)
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==> Fastest, but most complex
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====================
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= CCO/NACC =
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35
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====================
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CCO + NACC from E-UTRAN (connected/DRX) to GERAN (packet_idle)
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CCO + NACC rom GERAN (GPRS packet transfer) to E-UTRAN (RRC idle)
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==> Medium complexity, can work without intervention by the network.
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UEs request cell info via RIM and perform the cell change based on that info.
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== System information ==
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- CCN (Cell Change Notification) must be enabled in SI (UTRAN/3G:PSI3g EUTRAN:SI2q)
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44
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osmo-pcu already enables CCN in SI13
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== Messages (GERAN) ==
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RAN: PACKET_MEASUREMENT_ORDER
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RAN: PACKET_CELL_CHANGE_ORDER
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RAN: CHELL_CHANGE_CONTINUE
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RAN: PS_HANDOVER_COMMAND
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RAN: PACKET_NEIGHBOUR_CELL_DATA
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MS: PACKET_CELL_CHANGE_NOTIFICATION
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== Steps (GPRS) ==
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(UE makes sure that CCN (Cell Change Notification) is enabled in SI (UTRAN/3G:PSI3g EUTRAN:SI2q)
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- UE wants to change to a different cell on a different RAT, but does not have the system information to perform the
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cell change yet.
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- UE sends PACKET_CELL_CHANGE_NOTIFICATION to network to propose a cell (can be one or more)
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- Network sends PACKET_NEIGHBOUR_CELL_DATA back (multiple messages)
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- Network sends PACKET_CELL_CHANGE_CONTINUE, UE changes cell autonomously
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- (Network may also respond with PACKET_CELL_CHANGE_ORDER (CCO) or a PS_HANDOVER_COMMAND)
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MS PCU open5gs
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| | |
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|----PACKET_CELL_CHANGE_NOTIFICATION----->| |
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| +-----------------------------------------+
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|<------PACKET_NEIGHBOUR_CELL_DATA-----| |
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|<------PACKET_NEIGHBOUR_CELL_DATA-----| RIM RAN INFORMATION REQUEST |
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|<------PACKET_NEIGHBOUR_CELL_DATA-----| |
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|<------PACKET_NEIGHBOUR_CELL_DATA-----| |
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| +-----------------------------------------+
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|<------PACKET_CELL_CHANGE_CONTINUE-------| |
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== Interfaces ==
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Gb/BSSGP (2g/GPRS)
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Iu/RANAP (3g)
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Gn/GTPv1/RIM (SGSN<==>MME)
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S16/GTPv2/RIM (rel. 8 only, interconnects multiple SGSN)
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== Specs ==
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3gpp TS 44.060 (GPRS/RLCMAC), section 8.8 Network Assisted Cell Change procedures
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3gpp TS 48.018 (BSSGP), section 8c Signalling procedures between RIM SAPs
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86
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3gpp TS 25.413 (RANAP), section 9.2.3.30-9.2.3.32 (message descriptions)
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3gpp TS 29.060 (GTP-C), section 7.5.14, RAN Information Management Messages (RIM)
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section 7.7.43, RAN Transparent Container
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3gpp TS 23.060, section 8.1.5 RAN Information Management (RIM) procedures (Addressing, Routing, Relaying)
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== Open5gs ==
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grep for RIM:
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lib/gtp/v1/message.c: RIM related message definitions are present.
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lib/asn1c/: NGAP, S1AP, A lot of asn1c generated code.
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lib/gtp/v1/support/cache/tlv-msg-70.py
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96
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lib/gtp/v1/support/cache/tlv-type-list.py
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lib/ngap/ogs-ngap.h: includes some of the header files for the asn1c RIM message encoder/decoder
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lib/s1ap/ogs-s1ap.h: includes some of the header files for the asn1c RIM message encoder/decoder
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lib/sbi/openapi/model/ngap_ie_type.c: ngap_ie_typeArray[] with RIM stuff
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lib/sbi/openapi/model/ngap_ie_type.h: enum with RIM stuff
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==> Message definitions present, but no code that makes use of them.
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102
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== Open Questions ==
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104
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- ttcn3-hnbgw-test has no NACC tests. Does osmo-hnbgw have any RIM support? Is this in scope as well?
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- osmo-sgsn: We apparantly support Gn towards MME, but what about the traffic?
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106
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- osmo-sgsn: is RIM routing properly tested?
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107
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== Milestones ==
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- osmo-pcu: TTCN3 testsuite tests inter RAT inbound/outbound NACC and osmo-pcu behaves as expected
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110
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In this milestone we toughen osmo-pcu so that it will fully support 3G/4G NACC. This is our first step
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towards better interoperability.
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112
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ToDo: * Extend osmo-pcu and related TTCN3 testsuite so that 3G/4G PacketCellChangeNotification is
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is handled / tested properly
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- Osmo-pcu does not understand 3G/4G PacketCellChangeNotification, see:
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nacc_fsm.c:fill_neigh_key_from_bts_pkt_cell_chg_not()
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- TTCN3 libraries also do not model 3G/4G PacketCellChangeNotification, see:
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RLCMAC_CSN1_Types.ttcn:PacketCellChangeNotification
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* Extend osmo-pcu TTCN3 testsuite so that inbound NACC is tested
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119
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- osmo-pcu should support inbound NACC requests, but the TTCN3 tests do cover this
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120
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121
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- osmo-sgsn: Gn interface switching between GGSN and MME
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122
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This is an optional milestone since the MME can carry out all functions of a classic GGSN.
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When implemented, all non LTE capable UEs would get their IP packet anchor in the classic GGSN,
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all others would get the IP packet anchor in the EPC (evolved packet core).
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125
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- osmo-hnbgw: TTCN3 testsuite tests DirectInformationTransfer (RIM) and osmo-hnbgw behaves as expected
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Similar to osmo-pcu we toughen osmo-hnbgw so that it will fully support 3G/4G NACC.
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ToDo: * In hnbgw_ranap.c:ranap_rx_initiating_msg we can see that messages with procedure code
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DirectInformationTransfer are dropped. Those messages, which come from the HNB, will contain
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the RIM Ran Information Requests. (DirectInformationTransfer->InterSystemInformationTransferType->
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rIM-Transfer, see also 3GPP TS 25.413, section 9.1.54) Also in hnbgw_cn.c:cn_ranap_rx_initiating_msg()
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we do not know what to do with a DirectInformationTransfer. All this seems to be more or less just
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about transparently forwarding those messages to the CN.
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* Extend osmo-hnbgw TTCN3 testsuite so that it verifes that DirectInformationTransfer works.
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135
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- osmo-sgsn: OsmoSGSN has a TTCN3 test that tests a RAN information Request with a GERAN cell TC_bssgp_rim_single_report.
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This should be/is extended so that also UTRAN and EUTRAN cells are queried Also we need to add tests that check if the
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reverse direction actually works (MME asks via Gn interface for GERAN cell info).
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ToDo: * Extend TTCN3 testsuite so that it tests the GERAN originated RAN information Request with a 4G target
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cell. (Also add a test that tests the same with a 3G cell, the request might have to be routed through
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RANAP, so this might require the completion of the RANAP part first.) In sgsn_rim.c:sgsn_rim_rx_from_gb we
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see that we should be able to query GERAN and even EUTRAN cells. But apparantly we lack support for EUTRAN
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cells.
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* In osmo-iuh.git, iu_client.c:cn_ranap_handle_co we can see that no DirectInformationTransfer (Not to be
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confused with DirectTransfer) is supported. Also the code that uses the iu_client in osmo-sgsn has no
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knowlegde about DirectInformationTransfer, so RIM support for 3G/RANAP is missing and needs to be
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implemented.
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148
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- open5gs: A TTCN3 testsuite that tests the RIM capabilities exists and open5gs is extended so that RIM containers are routed
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between S1/ENBs and Gn/GTP.
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ToDo: * As it seems open5gs has no RIM support. The message definitions are present but no procedures are
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implemented. This means we have to extend open5gs with RIM capabilities first. We also need a testsuite
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to do the implementation, so adding RIM support and developing the testsuite will have to be done in
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parallel.
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====================
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= CR =
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159
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====================
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160
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161
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Cell Reselection from GRPS (Packet transfer mode or packet_idle) to E-UTRA (RRC idle)
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162
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Cell Reselection from E-UTRA (any state) to GERAN (packet_idle)
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==> Slowest method, UEs search for new cell as soon as they lose signal.
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== Steps ==
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- UE looses signal
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- State change: RRC_CONNECTED / GSM_CONNECTED => RRC_IDLE / PACKET_IDLE
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- Cell Reselection
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- Connection establishment on selected cell
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== Conclusion ==
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- This method is the simplest possible but also the most inefficient.
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- Simple because no communication betwen E-UTRAN and GERAN is required.
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- Already works with Osmocom and open5gs.
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