poll: Use the data_ind FN as time source for current frame

The FN of the data_ind taken from the DSP are monotonic, so latency
does not affect the detection of poll timeouts if these FN are used.
If the FN is larger than a poll_fn value, it can safely be assumed
that the poll response will not arrive later on.

Currently a max_delay of 60 frames is used, which has the drawback
that additional ~250ms will pass until a lost ACK is detected.

Using the data_ind's FN alone breaks the poll timeout detection if
there are no other MS sending data blocks.

This commit adds BTS::set_current_block_frame_number that is called
with the FN taken from data_ind messages. The max_delay is set to 0
which removes the additional delay, when this FN is used to detect
poll timeouts. So the average additional delay decreases with the
number of data_ind per time. The current_frame is updated unless it
seems to have been updated already (assumed if 0 < cur_fn - block_fn
< 500). Thus the time_ind has still priority to update the
current_frame value.

Sponsored-by: On-Waves ehf

1 files changed, 2 insertions, 0 deletions

diff --git a/src/bts.h b/src/bts.h
index e0f09b98..3dfe3f37 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -244,6 +244,7 @@ public:
 
 	/** TODO: change the number to unsigned */
 	void set_current_frame_number(int frame_number);
+	void set_current_block_frame_number(int frame_number);
 	int current_frame_number() const;
 
 	/** add paging to paging queue(s) */
@@ -301,6 +302,7 @@ public:
 
 private:
 	int m_cur_fn;
+	int m_cur_blk_fn;
 	struct gprs_rlcmac_bts m_bts;
 	PollController m_pollController;
 	SBAController m_sba;