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Currently old LLMEs and MM contexts that haven't been explicitly
detached or cancelled are not removed until another request with the
same IMSI is made. These stale entries may accumulate over time and
severely compromise the operation of the SGSN.
This patch implements age based LLME expiry, when the maximum age has
been reached, the corresponding MM context is cancelled. If such an MM
context doesn't exist, the LLME is unassigned directly.
The implementation works as follows.
- llme->age_timestamp is reset on each received PTP LLC message
- sgsn_llme_check_cb is invoked periodically (each 30s)
- sgsn_llme_check_cb sets the age_timestamp to the current time if
it has been reset
- sgsn_llme_check_cb computes the age and expires the LLME if
it exceeds gprs_max_time_to_idle()
Ticket: OW#1364
Sponsored-by: On-Waves ehf
[hfreyther: Fix typo in comment LMME -> LLME]
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The osmo-sgsn sends Status messages (or nothing in case of non
GMM/GSM) when the TLLI is unknown. This prevents the MS from
reconnecting.
This patch adds the initiation of an MT detach procedure to force a
re-attach to set up a valid LLE context if an LLE or an MM context
cannot be found. Since this can also be triggered by non-GMM SAPI
messages, a GPRS application callback sgsn_force_reattach_oldmsg is
added which in turn calls the GMM layer to generate the GSM 04.08
specific messages.
Note that the MS can be left in REGISTERED state after initially
wanting to detach itself, since it will receive a Detach Req
(re-attach) when sending a DEACT PDP CTX REQ after the SGSN or
gbproxy (P-TMSI patching enabled) has been restarted. This same
behaviour has been observed with another SGSN.
Sponsored-by: On-Waves ehf
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On an "unassignment" this code verifies that the LLME will vanish
from the list of LLMEs. We assume that this doesn't create a
memory leak.
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Currently LLC parsing is part of gprs_llc.c which needs large parts
of the SGSN code parsing to fulfill its link dependencies.
This patch moves the functions that just do plain parsing, dumping,
and FCS computation to a different file to avoid these dependencies
if LLC stateful processing is not needed. It also exposes
struct gprs_llc_hdr_parsed and enum gprs_llc_cmd publically.
Sponsored-by: On-Waves ehf
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In some situations (like MS reboot without prior DETACH or SGSN reboot
without prior MS detach), the LLC sequence numbers for UI mode could
be different on both sides.
The LLC spec unfortunately doesn't permit us to send something like a
FRMR in this case, but instructs us to silently discard the frame. At
that time the remote LLC entity will re-transmit the frame with the same
seqeunce number over and over again, which we will drop again and again.
The mthod used now will keep track of the last received UI sequence
number. If that number is retransmitted for three times in a row, then
we accept this sequence number and recover from that point on.
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GSM 04.64 8.4.2 asks to ignore UI frames if the DLCI is not known,
or if the "(V(UR)- 32) <= N(U) < V(UR)". E.g. if we want to have
V(UR) == 511 and this frame is dropped, we would ignore N(U)'s
0 to 510. Calculate the delta.
The code is based on Jonathan Santos's "LLC UI window" fix but the
issue was discovered independly.
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Using LLGMM-RESET.req, the GMM can request the LLC of the MS to reset
all its parameters, particularly the sequence numbers. We don't yet do
XID RESET retransmissions, and we don't yet generate a LLGMM-RESET.conf
primitive back to GMM.
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Summary of changes:
s/struct timer_list/struct osmo_timer_list/g
s/bsc_add_timer/osmo_timer_add/g
s/bsc_schedule_timer/osmo_timer_schedule/g
s/bsc_del_timer/osmo_timer_del/g
s/bsc_timer_pending/osmo_timer_pending/g
s/bsc_nearest_timer/osmo_timers_nearest/g
s/bsc_prepare_timers/osmo_timers_prepare/g
s/bsc_update_timers/osmo_timers_update/g
s/bsc_timer_check/osmo_timers_check/g
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This adds the bits that call into libosmocore (and its plugins)
to implement GPRS (LLC) encryption.
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* separate the LLME and LLE state in the LLC layer
* introduce gprs_llgmm_assign() function for LLGMM-ASSIGN.req primitive
* change QoS profile to match 'real' SGSN
* Update the new TLLI when assigning a P-TMSI
The result now is that the LLC layer is notified of TLLI changes, which in turn
means it doesn't allocate a new LLE structure every TLLI change, which again
in turn means that the UI frame sequence number does not reset to zero.
As a result, MS should no longer ignore frames based on wrong UI sequence number.
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When we send a downlink unit-data request via BSSGP, there is a lot
of information that needs to be copied from the mm context, such as
the IMSI, DRX parametes, MS radio access parameters, ...
This is a quite strange layering violation, since we now need to pass
a pointer to the MM ctx from GMM through LLC into BSSGP :(
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Don't allocate a LLC Entity just because BSSGP passes any random
SAPI/TLLI up to us. We can only do this for XID and UI frames
of the GMM SAPI.
Furthermore, add more comments and debug messages.
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libosmocore already uses them, it's time (at least for new code)
in openbsc to do the same.
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This branch contains the partial SGSN/GGSN implementation that
was originally developed as part of the gprs branch.
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