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.
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.
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
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.
Code to implement handover control logic. A yet-to-be-implemented
handover algorithm will call bsc_handover_start(old_lchan, new_bts)
to start the handover process.
This introduces the signals S_LCHAN_ACTIVATE_{ACK,NACK} and
S_LCAN_HANDOVER_{FAIL,COMPL,DETECT} as well as code that actually issues
those signals. The signals are relevant for a yet-to-be-written handover
control logic.
This is needed by a yet-to-be-implemented handover algorithm, after
it has allocated a new lchan for the MS. Also missing: handling
the actual HANDOVER COMPLETE / FAIL messages in response.
This patch extends struct gsm_meas_rep into a complete structure containing all
information from both uplink and downlink measurement results/reports.
This is a first step to provide this complete measurement data as a C structure
into a to-be-implemented handover decision algorithm.
- Make sure that on runtime the Radio Carrier can be
locked and unlocked. The vty code calls into the
Abis NM to lock/unlock the channel and the state is
stored there.
- Make sure that on start the Radio Carries remains
offline and we are not starting it. On start the
radio carrier is either locked or unlocked. This means
the RSL will not connect until the RF is unlocked. It
will connect then. To see RSL bringup failures one
needs to parse the RSL nack message.
- When the TRX is locked on startup the RSL link will
only be established after it will be unlocked.
The python script is a simple call-agent driving the
client. Currently it is sending a AuditEndpoint message
and is printing the result.
The bsc_mgcp.c is a standalone process that will implement
a MGCP Gateway for the MSC. On call handling the Call-Agent
will ask the Gateway to "CreateConnection" and then this
gateway needs to communicate with OpenBSC.
Currently CreateConnection,ModifiyConnection,DeleteConnection
and Endpoint auditing is implemented.
[mgcp] Send RSIP on start and on first receive of any message
Ignore the first request and send a RSIP. We do that because
we might tunnel UDP through some other things and have no direct
way to connect to the call-agent.
Also the transaction is not checked and we ignore the response
from the call-agent, actually we print the '200 ' or any other
value as unhandled...
[mgcp] Print the MGCP command next to the response code
This allows to see which commands were sent by the server
mgcp: Terminate it with a new line
[mgcp] Make number of endpoints static...
For now this is fixed to the number of endpoints as of the GSM
specification...
[mgcp] The endpoint names seem to be base 16... use strtoul to parse
Use strtoul to parse the base 16 number from the mgw string.
[mgcp] Log the endpoints as hex numbers...
[mgcp] Only send the RSIP on the first incoming message..
Remove call_agent option (also remove the number from the getopt
call).
[mgcp] Start couting at 1 for the mgcp
[mgcp] Slight attempt to improve the grammar of the strings
[mgcp] Share validation routines between DLCX and MDCX
[mgcp] Remove help for dead config options
[mgcp] Specify a different IN addr in the SDP records
In case of NAT traversal be able to listen on a given
interface (like 127.0.0.1) but claim to receive data
at the beginning of the tunnel.
[mgcp] Fix the static copy of the SDP file
WIP verify out factoring broken..
[mgcp] Introduce VTY to the mgcp for config file parsing...
Parse the MGCP config file via the VTY framework.
[mgcp] Handle SDP parameters through VTY..
Currently the payload type, name and rate can be specified
in the config file.
[mgcp] Add an option to bind all rtp ports early
This can be useful for testing and in deployment to make sure
no runtime resource limit can be hit.
[mgcp] Add some API doc comment
[mgcp] Convert the packets of the example server to ascii
This will allow to easily patch the call id... to run the
server in a loop and make it work with the mediagateway
[mgcp] Assign CI_UNUSED... to be more obvious...
[mgcp] Use DEBUG and not DEBUGPC and specially not printf
Improve the logging a bit in the mgcp
[mgcp] Change the fake server to change the call id
This assume the call-agent will just increment the id
as well.... this is true for our implementation
[mgcp] Generate the transaction id dynamically..
This way wireshark will be more happy about it...
[mgcp] Recognize responses from the network..
This is just recognizing the response code and
then is doing nothing with it. Also change the
script to generate response messages...
[mgcp] Improve debug messages for CRCX/MDCX..
Log on which ports the media gateway is listening
and where the other (server) gateway is located
Harald Welte
Harald Welte