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ISUP early media or inbound call with "no indication" ACM

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Dialogic SS7 and SIGTRAN Signalling

ISUP early media or inbound call with "no indication" ACM

  • Dear Colleagues,

    I am trying to investigate the possibility to play an early media in ISUP call setup scenario.

    I have captured the MTP3 pcap trace for call originated from Dialogic SPCI4 to a cell phone which is switched off.

    At this moment the Operator network plays an early media announcement and I was even able to record it to a sound file.

    This call is not charged. After observing the trace I could see that during that call Operator sends me ACM with BCI "no indication" and "cause indicator" parameter. ANM is not sent at all, but I wonder that I am able to hear the announcement.

    Now I need to do the same during the inbound call originated from a cell phone. I need to be able to play an early media.

    I tried gc_SetBilling with GCR_NOCHARGE, but the charging eventually takes place and announcement could not be heard until I send ANM.

    ACM in turn contains BCI indicators with a meaningful values.

    The questions are:

    • Is it possible to play an early media announcement in ISUP at all?
    • Is it possible to modify ACM BCI parameters: Called Party's Status Indicator, Called Party's Category Indicator and etc.?

    By the way, during the normal call to a cell phone which is ON I can see that Operator sends ACM with "no indication" and then after a few seconds send CPG wth BCI indicators.

  • Dear Colleagues,

    I have found the solution.

    Indeed SS7 supports early media by specifying certain parameters within ACM message.

    In my case sending Optional Backward Call Indicators set to "1" has helped. The value for this parameter means the "In-band information indicator" value to be "in-band information or an appropriate pattern is now available".

    After receiving this ACM MSC has started to receive an early voice stream and transferring it to mobile device.

    There could be another solutions to this though. More on this can be found here: tools.ietf.org/.../rfc3398

    specifically at chapters 7.2.5 (Early ACM received) and 7.2.6 (ACM received).

  • Hi Rauf,

    I'm also having the same issue that the other operator doesn't see the in-band-information-indicator set to "1" in the ACM sent by my Dialogic 2020 (ver 1.1). Is there any place that we can enable this?

    Best regards,

    Tharaka

  • Hi Tharaka,

    Have you checked your outgoing ISUP traffic, whether you have this parameter set?

  • Hi Rauf,

    Thank you for the reply. Actually, the call flow is Other Operator ISUP --> IMG 2020 --> SIP trunk. Yes, it is confirmed that the ACM IMG sends to the Other Operator does not have the in-band-information-indicator set to "1" . I couldn't find in the GUI configuration of IMG 2020 to set this. I've checked "BCI override" in the ISUP Channel Group but it does not have any configuration option indicating the in-band information indicator.

    Best regards,

    Tharaka

  • Hi Tharaka,

    If you mean that you captured the SS7 traffic and saw no BCI indication there and don't know how to set it then I'm afraid I can't help you because in my case I was doing all the stuff programmatically not through SIP gateway

  • Hi Rauf,

    Thank you for the reply. I found another way to get the bearer opened for the A-party to hear pre-call audio. Instead of setting  in-band-information-indicator set to "1" in the ACM, we could get the IMG 2020 to generate a CPG message by using RFC 3398 in the SS7 SIP (wiki.freepbx.org/.../SS7+ISUP+to+SIP+Interworking).

    Best regards,

    Tharaka