User manual

3.3. Incoming Call
3.3.1. GSM Gateway Ringing, Extension Dialling, Extension Ringing and Connection
Establishing
When the GSM Gateway receives a command from the GSM network and, if available,
the CLIP information, it starts ringing (i.e. generating the ringing voltage – whose timing is
programmable) into the PBX. The PBX registers the ringing and then, one of the
following situations may occur:
3.3.1.1 PBX without DISA = Selected Extension Ringing
In this case, the selected extension (or several extensions at the same time or
sequentially according to the PBX set-up) starts ringing and the calling subscriber will
not pay for the call until the ringing extension answers.
3.3.1.2 PBX with DISA, Intelligent Routing Off
In this case, the PBX answers and starts reproducing the so-called DISA message.
The GSM Gateway establishes connection immediately in order that the caller can
hear the message and dial the required extension.
3.3.1.3 PBX with DISA, Intelligent Routing On, and CLIP Present and Known
(Only for GSM calls. GSM gateway cannot receive CLIP from PSTN line.)
In this case, the PBX also answers and starts reproducing the DISA message. The
GSM Gateway, however, has found the caller’s number in its Intelligent Incoming Call
Routing Table and thus knows the extension to be called. Therefore, the GSM Gateway
does not establish connection immediately, but serves the DISA function (waits and dials
the extension number). Then, it establishes the connection and the calling subscriber can
hear the ringing tone
and the called subscriber.
3.3.1.4 PBX with DISA, Intelligent Routing On, but CLIP Absent or Unknown
In this case, the PBX also answers and starts reproducing the DISA message. The GSM
Gateway, however, has not found the caller’s number in its Intelligent Incoming Call
Routing Table (or has not received the CLIP). Then it can (according to its set-up) either
work as described in 3.3.1.2, or as described in 3.3.1.3, plus dial the operator’s number.
3.3.2. Call
With incoming calls, the GSM Gateway waits until the call is terminated, which situation is
the same as with an outgoing call.
Another differences between GSM and PSTN calls:
3.3.2.1 GSM incoming call
GSM call may be terminated forcibly if the GSM signal gets lost, for example, or in similar
situations.
During the GSM call, GSM gateway keeps PSTN line off-hook. This is important because
GSM gateway is not able to serve incoming call from PSTN, till PBX line is busy by GSM
call. If somebody will call to you (via PSTN line), he or she will get busy tone from public
exchange.
3.3.2.2 PSTN incoming call
During the PSTN call, incoming calls from GSM network are refused. (This is important
because GSM gateway is not able to serve two calls at a time. Without refuse, calling
party hears ringing, but it is not possible to ring to PBX.)
3.3.3. Connection Termination (End)
For GSM call termination, see chapter 3.1.9
For PSTN call termination, see chapter 3.2.9
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