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SRVCC: Parse Last Used E-UTRAN PLMN Id in Handover Request 

Whenever SRVCC EUTRAN->GERAN is performed by the CN, it will set the
Last Used E-UTRAN PLMN Id in order for the BSS to inform the MS
about EUTRAN neighbors once the call is over.
The last part (sending EUTRAN neighs) is already implemented, since same
thing is done as per CSFB. However, we lacked the first part, where the
EUTRAN PLMN Id is recorded for later use.

Actually, in both cases, we end up building the list of neighbors
without taking into accound the PLMN value (hence no filtering of
configured neighs), but it only sends such a list if any PLMN was stored
there, which means this patch is still necessary for a quick fallback to
4G after the call is over.

Related: SYS#5337
Depends: libosmocore.git Change-Id I0e55e947b6fef6dad0cf1a6c16b781bef4cc76c5
Change-Id: Ia5008f11a4c36ef8085a2037d4abddd131086e6e
This commit is contained in:
Pau Espin 2021-04-14 17:14:07 +02:00 committed by laforge
parent 8831160631
commit b0b76af0c3
3 changed files with 39 additions and 0 deletions
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1
TODO-RELEASE
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@ -8,3 +8,4 @@
# If any interfaces have been removed or changed since the last public release: c:r:0.
#library what description / commit summary line
libosmocore >1.5.1 needs osmo_bts_features_name(), osmo_bts_features_desc()
libosmogsm >1.5.1 enum entry GSM0808_FE_IE_LAST_USED_EUTRAN_PLMN_ID

2
include/osmocom/bsc/gsm_data.h
View File

@ -202,6 +202,8 @@ struct handover_in_req {
uint16_t msc_assigned_cic;
char msc_assigned_rtp_addr[INET6_ADDRSTRLEN];
uint16_t msc_assigned_rtp_port;
bool last_eutran_plmn_valid;
struct osmo_plmn_id last_eutran_plmn;
};
struct handover {

36
src/osmo-bsc/handover_fsm.c
View File

@ -417,6 +417,32 @@ static void handover_start_intra_bsc(struct gsm_subscriber_connection *conn)
lchan_activate(ho->new_lchan, &info);
}
/* 3GPP TS 48.008 § 3.2.2.58 Old BSS to New BSS Information */
static void parse_old2new_bss_info(struct gsm_subscriber_connection *conn,
const uint8_t* data, uint16_t len,
struct handover_in_req *req)
{
/* § 3.2.2.58: Information contained here shall take precedence over
duplicate information from Information Elements in the HANDOVER
REQUEST as long as the coding is understood by the new BSS */
/* § 3.2.2.58: <<Reception of an erroneous "Old BSS to New BSS
information" shall not cause a rejection of the HANDOVER REQUEST
message; the "Old BSS to New BSS information" information element
shall be discarded and the handover resource allocation procedure
shall continue>>. See also 3.1.19.7. */
struct tlv_parsed tp;
if (tlv_parse(&tp, &gsm0808_old_bss_to_new_bss_info_att_tlvdef, data, len, 0, 0) <= 0) {
LOG_HO(conn, LOGL_NOTICE, "Failed to parse IE \"Old BSS to New BSS information\"\n");
return;
}
if (TLVP_VAL(&tp, GSM0808_FE_IE_LAST_USED_EUTRAN_PLMN_ID)) {
req->last_eutran_plmn_valid = true;
osmo_plmn_from_bcd(TLVP_VAL(&tp, GSM0808_FE_IE_LAST_USED_EUTRAN_PLMN_ID),
&req->last_eutran_plmn);
}
}
/* 3GPP TS 48.008 § 3.2.1.8 Handover Request */
static bool parse_ho_request(struct gsm_subscriber_connection *conn, const struct msgb *msg,
struct handover_in_req *req)
@ -557,6 +583,10 @@ static bool parse_ho_request(struct gsm_subscriber_connection *conn, const struc
return false;
}
if ((e = TLVP_GET(tp, GSM0808_IE_OLD_BSS_TO_NEW_BSS_INFORMATION))) {
parse_old2new_bss_info(conn, e->val, e->len, req);
}
/* A lot of IEs remain ignored... */
return true;
@ -691,6 +721,12 @@ void handover_start_inter_bsc_in(struct gsm_subscriber_connection *conn,
info.encr.key_len = req->ei.key_len;
}
if (req->last_eutran_plmn_valid) {
conn->last_eutran_plmn_valid = true;
memcpy(&conn->last_eutran_plmn, &req->last_eutran_plmn,
sizeof(conn->last_eutran_plmn));
}
lchan_activate(ho->new_lchan, &info);
}