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While experimenting with CSFB, it was observed that when the UE returns to E-UTRAN after a CS call, the UE performs a Tracking Area Update with a combined Tracking Area/Location Area update and IMSI attach. Currently, Open5GS's MME simply responds with a TAU Accept message but does not inform the MSC/VLR. As a result, no further MT (Mobile Terminated) CS/SMS services are possible in cases where the MSC/VLR only attempts paging on GERAN. However, some MSC/VLR implementations with fast fallback may still attempt paging on E-UTRAN, allowing MT CS/SMS services to function intermittently. According to 3GPP TS 29.118 Section 5.2.2 Procedures in the MME, specifically Section 5.2.2.2.1, if the timer Ts6-1 is not running, the MME shall start the location update for non-EPS services procedure upon receiving a combined Tracking Area Update Request indicating combined TA/LA updating with IMSI attach. However, SGs timers are not implemented in Open5GS, which is a separate issue. To comply with the specification and ensure that the MSC/VLR is informed when the UE becomes reachable via SGs, the following changes have been implemented: 1. Delay UEContextReleaseCommand: When the active_flag is set to 0, the UEContextReleaseCommand is now delayed until the MME receives the TAU Complete message from the UE. This ensures that the UE has acknowledged the new P-TMSI before the network releases the context, maintaining proper synchronization between the UE and the network. 2. Include Mobile Identity Only When P-TMSI Changes: The Mobile Identity is now included in the Attach/TAU Accept messages only when the MSC/VLR updates the P-TMSI. This ensures that the UE receives the Mobile Identity information solely when there is an actual change in the P-TMSI, preventing unnecessary or incorrect handling of TAU Complete messages. 3. Send SGsAP-REALLOCATION-COMPLETE Conditionally: The SGsAP-REALLOCATION-COMPLETE message is now sent to the MSC/VLR only upon receiving a Attach/TAU Complete message from the UE. This confirmation indicates that the UE has successfully updated its P-TMSI, ensuring that the MSC/VLR is accurately informed of the change. 4. Handle P-TMSI Confirmation: When the MSC/VLR updates the P-TMSI, Open5GS stores the new P-TMSI in the next field of the mme_ue structure. Upon receiving the TAU Complete message from the UE, indicating acknowledgment of the new P-TMSI, Open5GS confirms the update by transferring the P-TMSI from the next field to the current field. This ensures that the MME maintains an accurate and up-to-date record of the P-TMSI as confirmed by the UE.
87 lines
2.1 KiB
C
87 lines
2.1 KiB
C
/*
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* Copyright (C) 2019 by Sukchan Lee <acetcom@gmail.com>
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*
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* This file is part of Open5GS.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include "test-app.h"
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abts_suite *test_mo_idle(abts_suite *suite);
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abts_suite *test_mt_idle(abts_suite *suite);
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abts_suite *test_mo_active(abts_suite *suite);
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abts_suite *test_mt_active(abts_suite *suite);
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abts_suite *test_mo_sms(abts_suite *suite);
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abts_suite *test_mt_sms(abts_suite *suite);
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abts_suite *test_tau(abts_suite *suite);
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abts_suite *test_crash(abts_suite *suite);
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const struct testlist {
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abts_suite *(*func)(abts_suite *suite);
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} alltests[] = {
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{test_mo_idle},
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{test_mt_idle},
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{test_mo_active},
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{test_mt_active},
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{test_mo_sms},
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{test_mt_sms},
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{test_tau},
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{test_crash},
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{NULL},
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};
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ogs_socknode_t *sgsap = NULL;
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static void terminate(void)
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{
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ogs_msleep(50);
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test_child_terminate();
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app_terminate();
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testvlr_sgsap_close(sgsap);
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test_epc_final();
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ogs_app_terminate();
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}
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static void initialize(const char *const argv[])
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{
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int rv;
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rv = ogs_app_initialize(NULL, NULL, argv);
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ogs_assert(rv == OGS_OK);
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test_epc_init();
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sgsap = testvlr_sgsap_server("127.0.0.2");
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ogs_assert(sgsap);
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rv = app_initialize(argv);
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ogs_assert(rv == OGS_OK);
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}
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int main(int argc, const char *const argv[])
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{
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int i;
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abts_suite *suite = NULL;
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atexit(terminate);
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test_app_run(argc, argv, "csfb.yaml", initialize);
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for (i = 0; alltests[i].func; i++)
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suite = alltests[i].func(suite);
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return abts_report(suite);
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}
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