This implements the handover algorithm (and associated parameters)
as described in Chapter 8 of the book "Performance Enhancements in
a Frequency |Hopping GSM Network" by Thomas Toftegard Nielsen and Jeroen
Wigard.
The parameters such as averaging windows are configured in struct
gsm_network. We keep some state to trakc up to 10 neighbors as
they are being reported from the MS.
This has so far only been tested in a network with two BTS that
have each other as neighbor. Networks with morge neighbors might
encounter bugs.
This allows us to block packets that we have received after the channel
is no longer being used. This is visible during handover, where we still
receive a measurement report after the MS has switched to the new channel.
This leftover measurement report then attempts to trigger another handover,
which si bogus and will fail - and thus only consumes resources.
With the new LCHAN_S_ACTIVE state, we can check for this when processing
the measurement report.
This provides two functions: get_meas_rep_avg() to obtain the sliding
window average of one particular field, and meas_rep_n_out_of_m_be()
to check if at least N out of M measurments are >= BE.
If a RF channel is assigned but no response is ever heard from
the phone, we will receive a CONNECTION FAIL from the BTS,
triggering a RF release freeing the channel. Then sometime later,
T3101 will expire as well and free the channel again ...
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
- Need to use sms.id for the ORDER BY since 'subscriber' also has 'id'
- Need to add the join clause between 'SMS' and 'subscriber'
- Add a LIMIT 1 (probably no impact for the db size we're dealing with
here, but with large DB and mysql/postgresql this can help the planner)
- (fix a wrong comment in passing ...)
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
This patch takes care of handling the RTP streams / sockets during
an in-call handover from one BTS to another BTS.
It only works in combination with rtp_proxy mode.
This is not really nice, but we will soon have multiple users of
the CRCX / MDCX / DLCX signals, and we cannot guarantee the ordering
of them. So as a workaround, we move the RTP socket creation and
deletion into the core abis_rsl codebase.
We cannot support in-call handover of calls without a RTP proxy,
since at the time of the handover the SSRC, sequence number and
timestamp of the RTP frames change.
Since the MNCC API can now send and receive frames to/from the MNCC
application, we can also implement a proxy this way. Not at the RTP/UDP packet
level, but at the 'TCH speech frame' level.
Especially for handover, we need this mode as the receiver in the BTS needs a
persistent SSRC and monotonic frame numbers / timestamps.
During handover, we will not send RTP frames for quite some time. However,
the way the rtp_send code is structured, it will increment the timestamp
with a fixed amount every time we send a frame, independent how much wallclock
time has actually passed.
This code is a hack to update the sequence number and timestamp in case it
seems to be wrong. It makes handover much more reliable.
Instead of passing TRAU frames down the MNCC API to the call control
application like MNCC, we now decode the TRAU frame into the actual codec
frame. We do the same with the RTP packets in case of ip.access and
thus have a unified format of passing codec data from the BTS to
an application, independent of the BTS type.
This is only implemented for V1 full-rate at the moment, and needs
to be fixed.
It seems that depending on the manufacturer, there is a need to include
the L2 pseudo-length in the SI5+SI6 messasges (SACCH FILLING)
Thanks to Dieter for pointing this out.
Multiple CM SERVICE REQUEST can happen on a single RR
connection, in this case, since the subscr reference is
tracked through lchan->subscr and will only be put'd once
on lchan_free, we need to make sure we don't get several
reference ....
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
'unknown' has a negative connotation for a case that's totally
normal so refer to it as 'new' so it doesn't sound like a problem.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
This introduces a new LOGP() macro together with LOGL_* definition to
support multiple log levels (severities) throughout the codebase.
Please note that the actual logging system does not use them yet,
in this patch we simply introduce the new macros at the caller site.
With this commit, we can successfully hand over a channel from one cell to
another cell. We implement asynchronous intra-BSC (but inter-BTS) handover.
Changes:
* introduce new DHO log category
* extend rsl_chan_activate_lchan() with argument for HO reference
* introduce actual minimal handover decision making in handover_decision.c
* various fixes to bsc_handover_start() in handover_logic.c
We will need this for the actual handover algorithm implementation, as we will
only know the current BTS and the BCCH ARFCN of the strongest cell in the
measurement reports. Using this new function, we can resolve the matching
gsm_bts.
Since we are keeping a bitvec of the neighbor cells, we can now use
bitvec_get_nth_set_bit() to determine the ARFCN for each reported
cell in the 04.08 MEASUREMENT REPORT.
We use a 1024-bit-sized bitvec to generate the BA and neighbor frequency list.
This bitvec is still generated from the list of all BTS's inside the BSC, but
this patch is the first step to generalize this, i.e. generate arbitrary
neighbor lists.
* introduce a new bitvec_get_bit_pos() function to determine the bit value
at a given position inside a bit vector
* make sure bitvec_{get,set}_bit_pos() share code as possible
In some cases, we can try to close the lchan a bit faster than our
lchan release timeout:
* After we've sent LOC UPD ACCEPT and MM INFO
* After a phone has confirmed the RELEASE of a call
The rationale is as following:
If we have NECI=1, then the phone will request a channel with CHREQ
"0100xxxx Originating speech call from dual-rate mobile station when TCH/H is
sufficient and supported by the MS for speech calls", then we will try to
allocate a TCH/H [as it is sufficient].
However, if there are no free TCH/H slots on the BTS, we abandon and can't
handle the MO call at all :(
We might read or write on the OML link when the BTS is
reset and will get SIGPIPE interrupt and be gone... Just
ignore the SIGPIPE we will get the "exception" on the next
run of bsc_select and kill the (old) OML link.
With ip.access, in case of TCH/H, we have one RTP stream for each half-slot
(lchan), not just one per on-air timeslot. This is quite different from
a classic BTS where the TRAU frames of the two TCH/H channels would be
part of the same 16k sub-slot in a E1 timeslot.
Before this commit, OpenBSC used templates for the SYSTEM INFO
1, 2, 3, 4, 5 and 6 messages. Those templates were patched in
various places to reflect the network config like ARFCN.
Now, we actually generate those SI messages ourselves, using
values from the configuration file, and even calculating neighbor
cell lists.
All bts'es that you have configured in OpenBSC will end up in
the neighbor cell list - which should be more than sufficient for
the current small-single-site networks.
Holger Hans Peter Freyther
Sylvain Munaut
Harald Welte