[asterisk-users] Understanding Call Handling In Asterisk

[varun.rapelly at spectross.com]

> >
>>  ----- Original Message ----- 
>>  From: Trevor Hammonds
>>  To: varun.rapelly at spectross.com ; Asterisk Users Mailing List - 
>> Non-Commercial Discussion
>>  Sent: Sunday, May 31, 2009 8:57 AM
>>  Subject: Re: [asterisk-users] Understanding Call Handling In Asterisk
>>
>>
>>
>>
>>  On May 29, 2009, Varun Rapelly <varun.rapelly at spectross.com> wrote:
>>
>>    Hi,
>>
>>    I am a newbie to Asterisk; need help understanding three-way 
>> conferencing &
>>    call-transfer features implemented over standard extensions i.e. on a
>>    TDM800P card (4 FXO + 4FXS)
>>
>>    In Asterisk I have observed that if an extension is already 
>> participating in
>>    an active call (e.g. Ext A & Ext B communicating):
>>
>>    1. An incoming call to one of these active extensions would be 
>> presented
>>    with call-wait beeps (e.g. Ext A receives call-wait beeps as Ext C is
>>    attempting to call Ext A).
>>
>>    2. The call waiting may be answered by pressing Hook-Flash, placing 
>> the
>>    previously active call on hold (e.g. C answered; A & C communicate; B 
>> placed
>>    on hold).
>>
>>    3. The calls could be toggled by subsequent Hook-Flash's (e.g. A & B
>>    communicate; C placed on hold).
>>
>>
>  Yes, this is normal behaviour on pretty much every analogue PBX or telco 
> switch.
>>
>>
>>
>>    Queries:
>>    1. If the extension which received call-wait beeps hangs-up then the 
>> call
>>    waiting/the call placed on hold returns as a new call. I was expecting 
>> the
>>    call to be transferred (A hangs-up, B & C communicate), how could the 
>> call
>>    be transferred? I expected this feature to be available in Asterisk as 
>> this
>>    is a very normal feature available on any PBX and used extensively in 
>> Call
>>    Transfer.
>>
>>
>>  When you transfer a call, the person initiating the transfer has to be 
>> MAKING a call.  Example:  Ext A receives a call from Ext B.  Ext A wants 
>> to transfer the call to Ext C.  Ext A puts the first call on hold with a 
>> hook flash, dials Ext C, then either waits for the Ext C to answer and 
>> announces the transfer (e.g. an attended transfer) OR simply hangs up as 
>> soon as the call to Ext C starts ringing (e.g. an un-attended or blind 
>> transfer).
>>
>  The behaviour you explain is not something available on any switch that I 
> am aware of, and would be highly problematic if it were.  If this 
> "feature" were available, you could get a circumstance where two people 
> who are calling you end up being bridged together on a call, unknown to 
> you.  As a bad example, your wife and your girlfriend end up talking to 
> each other because you hung up while one of them call-waited you while you 
> were talking to the other.
>
The scenario I was expecting was:

When Ext. A & B are in speech and A is getting call wait beeps from C.
Now if Ext. A hangs up, C's call will not be transferred to B but will come 
as
a new call to A. Well if A hangs up after answering C (B on hold), then C's 
call
would be transferred to B when A hangs-up.

Another point to be noted is when A & B are in speech. Either A could call C
by putting B on hold 'or' C could call A & present itself as a call-waiting.
The maximum loop count will never exceed 2 i.e. at any time you would
at-most have one active call & one call being held.

Hence, either ways if the second call be an incoming or an outgoing transfer 
shall
never occur without the will of transferer ;-).
>>
>>
>>    2. How could the extension that received call-wait beeps initiate a
>>    three-way conference with the other extensions (A, B & C in three-way
>>    conference)? I expected this feature to be available in Asterisk as 
>> this is
>>    a very normal feature available on any PBX and used extensively in 
>> 3-way
>>    Call Conference.
>>
>>
> Again, this is NOT a feature available on any analogue PBX that I am aware 
> of.  If it were, this would, again, mean that you may get unwanted parties 
> connected together.  With the above example, you answer your girlfriend's 
> call while talking to your wife, and all three of you end up in the same 
> conference.
>
What I was expecting is: 3-way conference would never be intiated by 
pressing
another flash but with a special key sequence (Feature Access Code /
Flash + some dtmf digit). Suppose A & B were in speech and A is getting
call wait beeps from C. Now if A presses "flash", the call is toggled i.e. A 
& C are
brought in speech and B is placed on hold. Subsequent "flashes", would also
have a similar behaviour. Well if A dials special key sequence (Feature 
Access
Code / Flash + some dtmf digit), then a 3-way conference would be 
established.

Again this can never happen accidentally.

>  Unfortunately, POTS lines do not handle transfering multiple inbound 
> calls very well (with call waiting).  This is not an Asterisk issue, POTS 
> lines were not designed to do anything other than handle a single call at 
> a time.  You may be able to handle transfering a call-waited call with 
> DTMF signalling.  I am certain someone else on the list will be able to 
> give you a definitive answer on that.
>
>
>  Sincerely,
>  Trevor Hammonds
>>
>>
>