bts: add IMMEDIATE ASSIGNMENT via PCH transmission

In situations where the PCU is co-located to the BSC, the IMMEDIATE ASSIGNMENT
for downlink TBFs must be sent via RSL and the BSC also must instruct the BTS
to transmit the IMMEDIATE ASSIGNMENT via PCH instead of AGCH. Eventually the
BSC must sent a confirmation message (follow-up patch) where the TLLI is used
as an identifer.

This new method will eventually replace the previous method that uses
the MAC block as an identifier. To remain compatible with older versions
of osmo-bsc, we will keep the old method until osmo-bts is migrated as

This patch also requires new features to be added to the PCU socket
interface the version number of the protocol is incremented from 0x0a to
0x0b. Version 0x0a will remain compatible and use the old method, while
version 0x0b will use the new method introduced with this patch.

Change-Id: I2a78651593323e8b9627c39918d949a33497b70f
Related: OS#5198
Philipp Maier 2 months ago
parent c82c948e99
commit 2353ed403f

@ -3,10 +3,12 @@
#include <osmocom/gsm/l1sap.h>
#include <arpa/inet.h>
#include <osmocom/gsm/protocol/gsm_04_08.h>
#include <osmocom/gsm/protocol/gsm_23_003.h>
#define PCU_SOCK_DEFAULT "/tmp/pcu_bts"
#define PCU_IF_VERSION 0x0a
#define PCU_IF_VERSION 0x0b
#define TXT_MAX_LEN 128
/* msg_type */
@ -269,6 +271,17 @@ struct gsm_pcu_if_neigh_addr_cnf {
} cgi_ps;
} __attribute__ ((packed));
/* Struct to send a (confirmed) IMMEDIATE ASSIGNMENT message via PCH. The struct is sent as a data request
* (data_req) under SAPI PCU_IF_SAPI_PCH_DT. */
struct gsm_pcu_if_pch_dt {
/* TLLI as reference for confirmation */
uint32_t tlli;
/* IMSI (to derive paging group) */
char imsi[OSMO_IMSI_BUF_SIZE];
/* GSM mac-block (with immediate assignment message) */
uint8_t data[GSM_MACBLOCK_LEN];
} __attribute__((packed));
struct gsm_pcu_if {
/* context based information */
uint8_t msg_type; /* message type */

@ -1103,7 +1103,6 @@ int bts_rcv_ptcch_rach(struct gprs_rlcmac_bts *bts, const struct rach_ind_params
void bts_snd_dl_ass(struct gprs_rlcmac_bts *bts, const struct gprs_rlcmac_dl_tbf *tbf)
uint16_t pgroup = ms_paging_group(tbf_ms(tbf));
int plen;
const struct gprs_rlcmac_pdch *pdch;
@ -1129,7 +1128,10 @@ void bts_snd_dl_ass(struct gprs_rlcmac_bts *bts, const struct gprs_rlcmac_dl_tbf
if (plen >= 0) {
bts_do_rate_ctr_inc(bts, CTR_IMMEDIATE_ASSIGN_DL_TBF);
pcu_l1if_tx_pch(bts, immediate_assignment, plen, pgroup);
if (the_pcu->pcu_if_version >= 0x0b)
pcu_l1if_tx_pch_dt(bts, immediate_assignment, plen, tbf->imsi(), tbf->tlli());
pcu_l1if_tx_pch(bts, immediate_assignment, plen, ms_paging_group(tbf_ms(tbf)));

@ -134,6 +134,8 @@ struct gprs_pcu {
struct si_cache *si_cache; /* ARFC+BSIC -> CGI PS cache */
struct osmo_timer_list update_stats_timer; /* Used to update some time_cc stats periodically */
uint8_t pcu_if_version;

@ -294,6 +294,24 @@ void pcu_l1if_tx_pch(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, uint1
pcu_tx_data_req(bts, 0, 0, PCU_IF_SAPI_PCH, 0, 0, 0, data, sizeof(data));
/* Send a block via the paging channel and require a confirmation by the receiving end */
void pcu_l1if_tx_pch_dt(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, const char *imsi, uint32_t tlli)
/* NOTE: This is in practice only used to transmit IMMEDIATE ASSIGNMENT messages through the paging channel and
* it is not guaranteed to work with other message types. The prepended TLLI will be used as an identifier in
* the confirmation message. */
struct gsm_pcu_if_pch_dt pch_dt;
pch_dt.tlli = tlli;
strcpy(pch_dt.imsi, imsi);[0] = (plen << 2) | 0x01;
bitvec_pack(block, + 1);
pcu_tx_data_req(bts, 0, 0, PCU_IF_SAPI_PCH_DT, 0, 0, 0, (uint8_t*)&pch_dt, sizeof(pch_dt));
int pcu_tx_neigh_addr_res_req(struct gprs_rlcmac_bts *bts, const struct neigh_cache_entry_key *neigh_key)
struct msgb *msg;
@ -734,14 +752,22 @@ static int pcu_rx_info_ind(struct gprs_rlcmac_bts *bts, const struct gsm_pcu_if_
if (llist_count(&the_pcu->bts_list) > 1)
LOGP(DL1IF, LOGL_ERROR, "more than one BTS regsitered at this PCU. This PCU has only been tested with one BTS! OS#5930\n");
if (info_ind->version != PCU_IF_VERSION) {
fprintf(stderr, "PCU interface version number of BTS (%u) is "
"different (%u).\nPlease re-compile!\n",
LOGP(DL1IF, LOGL_DEBUG, "Info indication received:\n");
/* NOTE: The classic way to confirm an IMMEDIATE assignment is to send the whole MAC block payload back to the
* PCU. So it is the MAC block itsself that serves a reference for the confirmation. This method has certain
* disadvantages so it was replaced with a method that uses the TLLI as a reference ("Direct TLLI"). This new
* method will replace the old one. The code that handles the old method will be removed in the foreseeable
* future. (see also OS#5927) */
if (info_ind->version == 0x0a) {
LOGP(DL1IF, LOGL_NOTICE, "PCUIF version 10 is deprecated. OS#5927\n");
} else if (info_ind->version != PCU_IF_VERSION) {
fprintf(stderr, "PCU interface version number of BTS/BSC (%u) is different (%u).\nPlease use a BTS/BSC with a compatble interface!\n",
info_ind->version, PCU_IF_VERSION);
LOGP(DL1IF, LOGL_DEBUG, "Info indication received:\n");
the_pcu->pcu_if_version = info_ind->version;
if (!(info_ind->flags & PCU_IF_FLAG_ACTIVE)) {
LOGP(DL1IF, LOGL_NOTICE, "BTS not available\n");

@ -149,6 +149,7 @@ void pcu_l1if_tx_ptcch(struct gprs_rlcmac_bts *bts,
void pcu_l1if_tx_agch(struct gprs_rlcmac_bts *bts, bitvec *block, int len);
void pcu_l1if_tx_pch(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, uint16_t pgroup);
void pcu_l1if_tx_pch_dt(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, const char *imsi, uint32_t tlli);
#ifdef __cplusplus