Repository forw the Osmocom BTS implementation.

This code implementes the Layer 2 and higher of a more or less
conventional GSM BTS (Base Transceiver Station) - however, using an
Abis/IP interface, rather than the old-fashioned E1/T1.

Specifically, this includes
 * BTS-Side implementation of TS 08.58 (RSL) and TS 12.21 (OML)
 * BTS-Side implementation of LAPDm (using libosmocore/libosmogsm)
 * A somewhat separated interface between those higher layer parts
   and the Layer1 interface.

Right now, only one hardware and Layer1 are supported:  The sysmocom
sysmoBTS.

There is some experimental and way incomplete code to use a couple of
OsmocomBB phones and run them in the BTS.  However, the required code
for the Calypso DSP code have not been written yet.  This would still
require a lot of work.

Some additional work is being done in using some parts of the OpenBTS
L1FEC and glue it against omso-bts.  This code is called osmo-trx and
requires the jolly/trx branch of this repository.

== Known Limitations ==

As of August 20, 2015, the following known limitations exist in this
implementation:

=== Common Core ===
 * No Extended BCCH support
 * System Information limited to 1,2,2bis,2ter,2quater,3,4,5,6,9,13
 * No RATSCCH in AMR
 * No OML (TS 12.21) alarms yet (temperature, ...)
 * Only single-TRX BTS at this point
 * Will reject TS 12.21 STARTING TIME in SET BTS ATTR / SET CHAN ATTR
 * No support for frequency hopping
 * No reporting of interference levels as part of TS 08.58 RF RES IND
 * No error reporting in case PAGING COMMAND fails due to queue overflow
 * No use of TS 08.58 BS Power and MS Power parameters
 * No support of TS 08.58 MultiRate Control
 * No support of TS 08.58 Supported Codec Types
 * No support of Bter frame / ENHANCED MEASUREMENT REPORT

=== osmo-bts-sysmo ===
 * No CSD / ECSD support (not planned)
 * GSM-R frequency band supported, but no NCH/ASCI/SoLSA
 * All timeslots on one TRX have to use same training sequence (TSC)
 * No multi-TRX support yet, though hardware+L1 support stacking
 * Makes no use of 12.21 Intave Parameters and Interference
   Level Boundaries
 * Doesn't yet include MAC address in Abis/IP Identity message
 * MphConfig.CNF can be returned to the wrong callback. E.g. with Tx Power
   and ciphering. The dispatch should take a look at the hLayer3.