Remove the global state from gprs_rlcmac_trigger_downlink_assignment
and walk up to the pcu_l1_if.cpp where I find the timeout handling
that should be part of the SBA and TBF functionality. In terms of
hierachies things start to be more clear.
There should be the BTS object. That holds the SBA and TBF Controllers
that can allocate TBFs and SBAs and will handle the timeout polling
for a BTS.
Global state makes mocking/writing tests more difficult. Continue
by removing direct usage of the bts and adding it as pointer to
the function calls (showing the true dependencies of the functions)
There really shouldn't be too many callers of state. Instead the
tbf should dispatch depending on the internal state. For now
introduce state_is and state_is_not accessor functions so we can
start to see who is using the internal state.
For mocking/unit-testing/emulation (and a dual trx-systems) having
global state is quite bad. Cut back on the usage of the global
struct gprs_rlcmac_bts. It also makes the complexity of certain
routines more clear.
The timing advance of any TBF is stored when it ends. Whenever a new TBF
with the same TLLI is created (downlink TBF), the stored TA is recalled.
This algorithm assumes that the mobile does not move too fast during
transfer. Also the mobile must start a connection in order to get correct
initial timing advance.
This algorithm does not implement the timing advance procedure as defined
in TS 04.60. To implement the standard timing advance procedure, the BTS
must decode RACH on certain bursts, the mobile is expected to send them.
This requires much more complexity to a transceiver like USRP/UmTRX or
Calypso BTS.
The algorithm was tested at TA >= 8 and works quite well.
The measurements include:
- DL bandwidth usage
- DL packet loss rate
- DL measurements by mobile
- UL measurements by BTS
In order to receive DL measurements from mobile, it must be enabled via
system information message at BSC.
This simpliefies the allocation process.
tfi_alloc is responsible to allocate a TFI, not a time slot.
The first time slot available depends on multislot class and on other
ongoing TBF (concurrent TBFs), so it is part of the allocation
algorithm to select it.
The slots are choosen in a way that later selection of slots for
concurrent TBFs will have the same downlink/uplink control channel
(PACCH).
This is required for polling acknowledge of new TBF assignment on PACCH.
The MS will always have the same PACCH uplink slot while beeing in packet
transfer mode.
Some MS will leave packet transfer mode, if TAI is given, but no timing
advance control messages are sent on PTCCH. This could results in
permanent loss of larger packets.
It is essential to initialize the first_fin_ack variable.
Also it is essential not to free TBF, in case the final ack is not
received, but all frames have been acked. In this special case, we resend
the final block again and again (and poll), until we receive the final
ack.
It is quite essential. It shows how TBFs are related and helps to estimate
states and timers (timeouts) of the MS.
In order to use it, it must be defined by a switch at gprs_rlcmac.h.
In this case the mobile has lost existing flows, so it make sense to free
them. The TFI(s) can be re-used immidiately, because they are not
associated by MS anymore.
This is required, since we may change slot allocation. In case of a
change, we do not want to be unable to change, if the same TFI on one of
the other slots is already in use by a different TBF (having same TFI, but
on different slot).
It is mandatory to support it because MS may request a single block.
In this case the network must assign a single block.
It is possible to force single block allocation for all uplink requests
on RACH. (VTY option)
Both flags can be used to determine wether assignment must be sent on PCH
or on AGCH. Before contention resolution is done, mobile will ignore
downlink assinment. When final uplink acknowledge was sent, the mobile
will go back to PCH after reception of akcnowledge.
Holger Hans Peter Freyther