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[MME] Fix GUTI <-> RAI/PTMSI derivation functions

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The algorithms described in 3GPP TS 23.003 Ch. 2.8.2.1.2 an 2.8.2.2.2
are not directly the inverse of each other.

To send a SGSN Context Request (in 2G -> 4G mobility) the algorithm in
2.8.2.2.2 has to be done in reverse (like mentioned in 2.8.2.2.3 -
Mapping in the new MME).

When parsing an SGSN Context Request (for 4G -> 2G mobility) the reverse
of 2.8.2.1.2 (as described in 2.8.2.1.3) has to be used.
PTMSI signature handling is added in a separate commit.
This commit is contained in:
Daniel Willmann
2024-03-01 20:07:26 +01:00
committed by Sukchan Lee
parent 9e19d28c4b
commit 2e180796e4
4 changed files with 9 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
src/mme/emm-sm.c
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@@ -504,7 +504,7 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e,
if (emm_tau_request_ue_comes_from_gb_or_iu(&message->emm.tracking_area_update_request)) {
ogs_info("TAU request : UE comes from SGSN, attempt retrieving context");
guti_to_rai_ptmsi(&mme_ue->next.guti, &rai, NULL, NULL);
guti_to_rai_ptmsi(&mme_ue->next.guti, &rai, NULL);
sgsn = mme_sgsn_find_by_routing_address(&rai, 0xffff);
if (!sgsn) {
ogs_plmn_id_t plmn_id;

8
src/mme/mme-gn-build.c
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@@ -194,7 +194,6 @@ ogs_pkbuf_t *mme_gn_build_sgsn_context_request(
ogs_gtp1_sgsn_context_request_t *req = NULL;
ogs_nas_rai_t rai;
mme_p_tmsi_t ptmsi;
uint32_t ptmsi_sig;
ogs_gtp1_gsn_addr_t mme_gnc_gsnaddr, mme_gnc_alt_gsnaddr;
int gsn_len;
int rv;
@@ -206,11 +205,13 @@ ogs_pkbuf_t *mme_gn_build_sgsn_context_request(
req = &gtp1_message.sgsn_context_request;
memset(&gtp1_message, 0, sizeof(ogs_gtp1_message_t));
guti_to_rai_ptmsi(&mme_ue->next.guti, &rai, &ptmsi, &ptmsi_sig);
guti_to_rai_ptmsi(&mme_ue->next.guti, &rai, &ptmsi);
req->imsi.presence = 0;
req->routeing_area_identity.presence = 1;
/* Needs to be big-endian */
rai.lai.lac = htons(rai.lai.lac);
req->routeing_area_identity.data = &rai;
req->routeing_area_identity.len = sizeof(ogs_nas_rai_t);
@@ -219,9 +220,6 @@ ogs_pkbuf_t *mme_gn_build_sgsn_context_request(
req->packet_tmsi.presence = 1;
req->packet_tmsi.u32 = be32toh(ptmsi);
req->p_tmsi_signature.presence = 1;
req->p_tmsi_signature.u24 = ptmsi_sig;
req->ms_validated.presence = 0;
req->tunnel_endpoint_identifier_control_plane.presence = 1;

10
src/mme/mme-gn-handler.c
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@@ -69,22 +69,20 @@ static int decode_global_enb_id(S1AP_Global_ENB_ID_t *glob_enb_id, const uint8_t
return OGS_OK;
}
/* 3GPP TS 23.003 2.8.2.1 Mapping from GUTI to RAI, P-TMSI and P-TMSI signature */
void guti_to_rai_ptmsi(const ogs_nas_eps_guti_t *nas_guti, ogs_nas_rai_t *rai, mme_p_tmsi_t *ptmsi, uint32_t *ptmsi_sig)
/* 3GPP TS 23.003 2.8.2.2 Mapping RAI and P-TMSI from GUTI (in the MME) */
void guti_to_rai_ptmsi(const ogs_nas_eps_guti_t *nas_guti, ogs_nas_rai_t *rai, mme_p_tmsi_t *ptmsi)
{
rai->lai.nas_plmn_id = nas_guti->nas_plmn_id;
rai->lai.lac = nas_guti->mme_gid;
rai->rac = nas_guti->mme_code;
rai->rac = (nas_guti->m_tmsi >> 16) & 0xff;
if (ptmsi)
*ptmsi = 0xC0000000 |
(nas_guti->m_tmsi & 0x3f000000) |
(nas_guti->mme_code & 0x0ff) << 16 |
(nas_guti->m_tmsi & 0x0000ffff);
if (ptmsi_sig)
*ptmsi_sig = (nas_guti->m_tmsi & 0x00ff0000);
}
/* 3GPP TS 23.003 2.8.2.2 Mapping from RAI and P-TMSI to GUTI */
/* 3GPP TS 23.003 2.8.2.1 Mapping GUTI from RAI, P-TMSI and P-TMSI signature (in the MME) */
static void rai_ptmsi_to_guti(const ogs_nas_rai_t *rai, mme_p_tmsi_t ptmsi, uint32_t ptmsi_sig, ogs_nas_eps_guti_t *nas_guti)
{
nas_guti->nas_plmn_id = rai->lai.nas_plmn_id;

2
src/mme/mme-gn-handler.h
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@@ -45,7 +45,7 @@ void mme_gn_handle_ran_information_relay(
ogs_gtp_xact_t *xact, ogs_gtp1_ran_information_relay_t *req);
void guti_to_rai_ptmsi(const ogs_nas_eps_guti_t *nas_guti, ogs_nas_rai_t *rai,
mme_p_tmsi_t *ptmsi, uint32_t *ptmsi_sig);
mme_p_tmsi_t *ptmsi);
#ifdef __cplusplus
}