doc/tbf.txt: Update and improve some information

Change-Id: I3cd643ef462637708c69895c62c488554a428571
changes/11/23911/2
Pau Espin 2 years ago
parent 039ee8200a
commit f593fc5cbb
  1. 36
      doc/tbf.txt

@ -117,13 +117,17 @@ Control TS:
Polling:
In order to poll uplink control block from MS, a special poll state and
frame number is stored at TBF. The scheduler reads that value and will not
assign uplink resource for other TBFs at that frame number.
When there is no uplink transmission received on the block, a timeout is
indicated by layer 1 interface. There are two ways of checking timeout:
- The received frame is bad (BFI).
- The GSM indicates that the block should have been already received.
frame number is stored at PDCH UL Controller. The scheduler reads that value
and will not assign uplink resource for other TBFs at that frame number.
On receipt of an Uplink RLCMAC block, it's the duty of each specific message
handler to release the expectancies previously stored in the PDCH UL
Controller. After the specific handler returns, the generic return path will
expire all reserved events up to the curent FN for that PDCH, eventually
calling timeout functions on TBFs and SBAs owning those reservations. Hence,
the layer 1 interface is expected to provide DATA.ind for each FN block,
containing data=0 if decoding failed, in order to keep the clock up-to-date in
upper layers.
Because polling requires uplink response from MS, the polling must be
performed at control TS.
@ -131,13 +135,21 @@ Polling:
Data structures of TBFs and PDCHs:
There is a global structure for BTS.
There is a global structure for PCU (struct gprs_pcu the_pcu).
A BTS is created and put into PCU's list for each PCUIF INFO_IND with a unique
bts_nr received.
The BTS structure has 8 TRX structures.
Each BTS structure has 8 TRX structures.
Each TRX structure has 8 PDCH structures, one for each timeslot.
There are two linked lists of TBF instances:
Each BTS structure has a list of MS (struct GprsMs).
Each MS can have 1 UL TBF and 1 DL TBF, and 1 TBF is always assigned to an
existing GprsMS structure.
Each BTS also has two linked lists of TBF instances:
- uplink TBFs
- downlink TBFs
@ -158,4 +170,6 @@ Data structures of TBFs and PDCHs:
On release of a TBF, the link to this PDCH is removed from all assigned
PDCHs. The TBF is removed from the list of TBFs. The TBF is destroyed.
GprsMs structures are kept alive for a while once they become unused, in order to
have a cache of MS related information it would otherwise need to acquire
again once it interacts with the PCU again.

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