OsmocomBB

h1. Call Hold SS

Call Hold (HOLD) is specified together with Call Waiting (CW).

h2. Relevant Specifications

* "3GPP TS 22.083: Call Waiting (CW) and Call Hold (HOLD) supplementary service; Stage 1"

* "3GPP TS 23.083: Call Waiting (CW) and Call Hold (HOLD) supplementary service; Stage 2":http://www.etsi.org/deliver/etsi_ts/123000_123099/123083/14.00.00_60/ts_123083v140000p.pdf

** contains SDL state diagrams for VLR and MSC

* "3GPP TS 24.010: Supplementary services specification"

* "3GPP TS 24.080: supplementary services specification; Formats

and coding"

* "3GPP TS 24.083: Call Waiting (CW) and Call Hold (HOLD) supplementary service; Stage 3":http://www.etsi.org/deliver/etsi_ts/124000_124099/124083/14.00.00_60/ts_124083v140000p.pdf

** contains information on signaling on L3 interface between MS and MSC

h2. Notes

* the HOLD state is not a state in the 24.007/24.008 call control state machine, but an auxiliary state machine:

** *Idle* before/after any HOLD or after HOLD REJECT.

** *Hold request* HOLD sent but no response yet

** *Call Held* after successful HOLD operation

** *Retrieve request* RETRIEVE sent but no response yet

h3. notification of other party

The other party is notified if SS-screening != 0:

** Facility/Invoke/NotifySS/HOLD

h3. HOLD activation

* MS sends HOLD

* MSC responds with HOLD ACK in successful case

* MSC responds with HOLD REJECT in error case (#29: rejected, #50: not subscribed, #69: not implemented, ...)

h3. RETRIEVE activation

* MS sends RETRIEVE

* MSC responds with RETRIEVE ACK in successful case

* MSC responds with RETRIEVE REJECT in unsuccessful case

h3. altenating between calls

The HOLD/RETRIEVE messages contain the regular CC transaction identifer, which is used to differentiate different calls.  You can put one call on hold and subsequently retrieve another.