move openbsc/* to repos root

This is the first step in creating this repository from the legacy openbsc.git.

Like all other Osmocom repositories, keep the autoconf and automake files in
the repository root. openbsc.git has been the sole exception, which ends now.

Change-Id: I9c6f2a448d9cb1cc088cf1cf6918b69d7e69b4e7

1 files changed, 95 insertions, 0 deletions

diff --git a/doc/channel_release.txt b/doc/channel_release.txt
new file mode 100644
index 000000000..c9cdfebca
--- /dev/null
+++ b/doc/channel_release.txt
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+
+GSM 04.08 7.1.7 / 9.1.7		RR CHANNEL RELESE
+
+RSL 08.58 3.4 / ?		RLL Link Release Request
+
+RSL 08.58 4.6 / 8.4.5		DEACTivate SACCH
+	* Deactivate SACCH according to Channel Release Proc 04.08
+	* to be sent after RR CHANNEL RELEASE is sent to MS
+
+RSL 08.58 4.7 / 8.4.14		RF CHANnel RELease
+	* tells the BTS to release a radio channel
+	* "when an activated radio channel is no longer needed"
+	* BTS responds with RF CHANnel RELease ACKnowledge
+
+
+GSM 04.08 3.4.13: RR connection release procedure
+
+* network sends RR CHANNEL RELEASE to MS on the DCCH
+  * start T3109
+  * deactivate SACCH
+* MS disconnects main signalling link (by sending DISC)
+  * all other data links are disconnected by local end link release
+* network receives DISC (BTS sends RLL REL IND to BSC)
+  * stop T3109
+  * start T3111 
+* when T3111 times out, the network can reuse the channls
+* if T3109 times out, the network deactivates the channels 
+  and can reuse them
+  * this probably means simply RF CHANnel RELease
+
+
+== Implementation in OpenBSC ==
+
+There are two possible reasons a gsm_subscriber_connection
+will be released. One is a network failure, the other is
+the completion of an operation/transaction.
+
+=== Failure ===
+The BSC API will call the gsm_04_08.c:gsm0408_clear_request callback
+and the MSC part will release all transactions, operations and such
+and the channels will be released as error case.
+
+=== Success ===
+Every time an 'operation' or 'transaction' is finished msc_release_connection
+will be called and it will determine if the gsm_subscriber_connection can
+be released.
+
+In case it can be released bsc_api.c:gsm0808_clear will be called
+which will release all lchan's associated with the connection. For the
+primary channel a SACH Deactivate will be send with the release
+reason NORMAL RELEASE.
+
+
+bsc_api.c:gsm0808_clear
+	* Release a channel used for handover
+	* Release the primary lchan with normal release, SACH deactivate
+
+chan_alloc.c:lchan_release(chan, sacch_deactivate, reason)
+	* Start the release procedure. It is working in steps with callbacks
+	  coming from the abis_rsl.c code.
+	* Release all SAPI's > 0 as local end (The BTS should send a
+	  REL_CONF a message)
+	* Send SACH Deactivate on SAPI=0 if required.
+	* Start T3109 (stop it when the main signalling link is disconnected)
+	  or when the channel released. On timeout start the error handling.
+	* abis_rsl.c schedules the RSL_MT_RF_CHAN_REL once all SAPI's are
+	  released and after T3111 has timed out or there is an error.
+
+RX of RELease INDication:
+        * Calls internal rsl_handle_release which might release the RF.
+
+RX of RELease CONFirmation:
+        * Calls internal rsl_handle_release which might release the RF.
+
+* RX of RF_CHAN_REL_ACK
+	* call lchan_free()
+
+
+=== Integration with SMS ===
+
+* RX of CP_ERROR or unimplemented MT
+	* trigger trans_free() which will msc_release_connection()
+
+* CP TC1* expired while waiting for CP-ACK
+	* trigger trans_free() which will msc_release_connection()
+
+* RX of RP_ERROR
+	* trigger trans_free() which will msc_release_connection()
+	
+* TX of CP-ACK in MT DELIVER
+	* trigger trans_free() which will msc_release_connection()
+
+* RX of CP-ACK in MO SUBMIT
+	* trigger trans_free() which will msc_release_connection()
+