scheduler: fix handling of PTCCH/U and PTCCH/D logical channels

According to 3GPP TS 45.010, section 5.6.2, for packet-switched
channels the BTS shall monitor the delay of the Access Bursts
sent by the MS on PTCCH and respond with timing advance values
for all MS performing the procedure on that PDCH.

According to 3GPP TS 45.002, section 3.3.4.2, PTCCH (Packet Timing
advance control channel) is a packet dedicated channel, that is
used for continuous Timing Advance control (mentioned above).

There are two sub-types of that logical channel:

  - PTCCH/U (Uplink): used to transmit random Access Bursts
    to allow estimation of the Timing Advance for one MS in
    packet transfer mode.

  - PTCCH/D (Downlink): used by the network to transmit
    Timing Advance updates for several MS.

As per 3GPP TS 45.003, section 5.2, the coding scheme used for
PTCCH/U is the same as for PRACH as specified in subclause 5.3,
while the coding scheme used for PTCCH/D is the same as for
CS-1 as specified in subclause 5.1.1.

The way we used to handle both PTCCH/U and PTCCH/D is absolutely
wrong - they have nothing to do with xCCH coding. Instead, we
need to use tx_pdtch_fn() for Downlink and rx_rach_fn() for Uplink.

In l1sap_ph_rach_ind() we need to check if an Access Burst was
received on PTCCH/U and forward it to OsmoPCU with proper SAPI
value (PCU_IF_SAPI_PTCCH). To be able to specify a SAPI, a new
parameter is introduced to pcu_tx_rach_ind().

Change-Id: I232e5f514fbad2c51daaa59ff516004aba97c8a3
Related: OS#4102

1 files changed, 1 insertions, 1 deletions

diff --git a/include/osmo-bts/pcu_if.h b/include/osmo-bts/pcu_if.h
index 114f87d1..f34e0cdc 100644
--- a/include/osmo-bts/pcu_if.h
+++ b/include/osmo-bts/pcu_if.h
@@ -12,7 +12,7 @@ int pcu_tx_data_ind(struct gsm_bts_trx_ts *ts, uint8_t is_ptcch, uint32_t fn,
 	uint16_t arfcn, uint8_t block_nr, uint8_t *data, uint8_t len,
 		    int8_t rssi, uint16_t ber10k, int16_t bto, int16_t lqual);
 int pcu_tx_rach_ind(struct gsm_bts *bts, int16_t qta, uint16_t ra, uint32_t fn,
-	uint8_t is_11bit, enum ph_burst_type burst_type);
+	uint8_t is_11bit, enum ph_burst_type burst_type, uint8_t sapi);
 int pcu_tx_time_ind(uint32_t fn);
 int pcu_tx_pag_req(const uint8_t *identity_lv, uint8_t chan_needed);
 int pcu_tx_pch_data_cnf(uint32_t fn, uint8_t *data, uint8_t len);