diff options
Diffstat (limited to 'src/bts.cpp')
| -rw-r--r-- | src/bts.cpp | 71 |
1 files changed, 57 insertions, 14 deletions
diff --git a/src/bts.cpp b/src/bts.cpp index 21e9d968..548d0009 100644 --- a/src/bts.cpp +++ b/src/bts.cpp @@ -34,6 +34,7 @@ extern "C" { #include <osmocom/core/msgb.h> #include <osmocom/core/stats.h> #include <osmocom/gsm/protocol/gsm_04_08.h> + #include <osmocom/gsm/gsm_utils.h> } #include <arpa/inet.h> @@ -41,6 +42,9 @@ extern "C" { #include <errno.h> #include <string.h> +#define RFN_MODULUS 42432 +#define RFN_THRESHOLD RFN_MODULUS / 2 + extern void *tall_pcu_ctx; static BTS s_bts; @@ -516,6 +520,57 @@ int BTS::rcv_imm_ass_cnf(const uint8_t *data, uint32_t fn) return 0; } +/* Determine the full frame number from a relative frame number */ +uint32_t BTS::rfn_to_fn(uint32_t rfn) +{ + uint32_t m_cur_rfn; + uint32_t fn; + uint32_t fn_rounded; + + /* Note: If a BTS is sending in a rach request it will be fully aware + * of the frame number. If the PCU is used in a BSC-co-located setup. + * The BSC will forward the incoming RACH request. The RACH request + * only contains the relative frame number (Fn % 42432) in its request + * reference. This PCU implementation has to fit both scenarios, so + * we need to assume that Fn is a relative frame number. */ + + /* Ensure that all following calculations are performed with the + * relative frame number */ + rfn = rfn % 42432; + + /* Compute an internal relative frame number from the full internal + frame number */ + m_cur_rfn = m_cur_fn % RFN_MODULUS; + + /* Compute a "rounded" version of the internal frame number, which + * exactly fits in the RFN_MODULUS raster */ + fn_rounded = m_cur_fn - m_cur_rfn; + + /* If the delta between the internal and the external relative frame + * number exceeds a certain limit, we need to assume that the incoming + * rach request belongs to a the previous rfn period. To correct this, + * we roll back the rounded frame number by one RFN_MODULUS */ + if (abs(rfn - m_cur_rfn) > RFN_THRESHOLD) { + LOGP(DRLCMAC, LOGL_DEBUG, + "Race condition between rfn (%u) and m_cur_fn (%u) detected: rfn belongs to the previos modulus %u cycle, wrappng...\n", + rfn, m_cur_fn, RFN_MODULUS); + if (fn_rounded < RFN_MODULUS) { + LOGP(DRLCMAC, LOGL_DEBUG, + "Cornercase detected: wrapping crosses %u border\n", + GSM_MAX_FN); + fn_rounded = GSM_MAX_FN - (RFN_MODULUS - fn_rounded); + } + else + fn_rounded -= RFN_MODULUS; + } + + /* The real frame number is the sum of the rounded frame number and the + * relative framenumber computed via RACH */ + fn = fn_rounded + rfn; + + return fn; +} + int BTS::rcv_rach(uint16_t ra, uint32_t Fn, int16_t qta, uint8_t is_11bit, enum ph_burst_type burst_type) { @@ -536,20 +591,8 @@ int BTS::rcv_rach(uint16_t ra, uint32_t Fn, int16_t qta, uint8_t is_11bit, if (is_11bit) rach_frame_11bit(); - /* Note: If a BTS is sending in a rach request it will be fully aware - * of the frame number. If the PCU is used in a BSC-co-located setup. - * The BSC will forward the incoming RACH request. The RACH request - * only contains the relative frame number (Fn % 42432) in its request - * reference. This PCU implementation has to fit both secenarious, so - * we need to assume that Fn is a relative frame number. */ - - /* Ensure that all following calculations are performed with the - * relative frame number */ - Fn = Fn % 42432; - - /* Restore the full frame number - * (See also 3GPP TS 44.018, section 10.5.2.38) */ - Fn = Fn + m_cur_fn - m_cur_fn % 42432; + /* Determine full frame number */ + Fn = rfn_to_fn(Fn); LOGP(DRLCMAC, LOGL_DEBUG, "MS requests UL TBF on RACH, " "so we provide one: ra=0x%02x Fn=%u qta=%d is_11bit=%d:\n", |