[asterisk-users] Issue between Asterisk Queue and GSM gateway when trying to use call waiting feature

Matthew Jordan mjordan at digium.com
Mon Dec 8 09:51:38 CST 2014

On Fri, Dec 5, 2014 at 3:23 PM, Rodrigo Montiel
<guevara2309 at yahoo.com.ar> wrote:
> Hi masters,
> I’m not an expert on this my friends, but I’m trying to understand which the
> expected behaviour is from Asterisk side when you deal with the following
> scenario:
> Caller —> GSM Gateway with SIM card A —> Asterisk queue —> extension 1000
> GSM gateway with call waiting activated on SIM A
> Queue with “skip busy agent” disabled and ringall strategy.
> SIP extension 1000 with call waiting activated, and member of Asterisk
> queue.
> a) One Caller calls to SIM card A of GSM Gateway, call is forwarded to
> Asterisk queue where SIP extension 1000 answers.
> b) New Caller calls the same SIM card A of GSM gateway (it has call waiting
> activated on the sim card), call is forwarded to Asterisk queue to the same
> extension 1000 and a pop-up appears with the second call.
> c) extension 1000 accepts it so put on hold first call, then try to pickup
> the new one.
> The thing is that the SIP re-invite with sendonly attribute can be seen from
> extension 1000 to Asterisk queue, but this SIP invite is not being forwarded
> to GSM gateway. So the GSM gateway keeps waiting for it and because it never
> appears the 1st call is dropped.
> Maybe you have had this issue in the past. I know that Im not an expert, but
> I have been researching a lot and trying to vary configurations without
> clues.
> The question is: Is it expected for the Asterisk queue to redirect this
> on-hold message (SIP re-invite with sendonly media attribute) to the GSM
> gateway so it can manage it call waiting feature on the same SIM card?
> If we repeat the same scenario without queue intervention (i.e. call goes
> directly to the extension) the SIP re-invite floods normally between
> Asterisk and GSM gateway, so GSM gateway can decide what to do with the
> call.
> I have no specific queue configuration, seems that queues.conf does not have
> any parameter to allow  this behaviour of re-sending re-invite/on-hold
> messages.
> Vendor from GSM gateway side is pointing that “Asterisk js not resending
> on-hold message”.

Asterisk is a back to back user agent. As such, it does not "forward"
or proxy any SIP messages. The re-INVITE sent from the SIP device
represented by extension 1000 in your scenario is handled by Asterisk,
and causes the channel on the other side of the bridge with that SIP
channel to be put on Hold.

There is no mechanism in Asterisk today to pass through a re-INVITE to
initiate a remote hold.

Matthew Jordan
Digium, Inc. | Engineering Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: http://digium.com & http://asterisk.org

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