This document discusses a problem where a public switched telephone network (PSTN) caller does not hear a ring back when calling an IP phone.
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This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
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There are some situations in which a gateway may intermittantly fail to provide Ring Back Tone (RBT) to an incoming ISDN caller. This problem has been seen on local, long distance, and international calls.
The Gateway generates ring back toward the network side (PSTN or private automatic branch exchange [PABX]), if the setup contains Progress IE = 3, meaning the originating address (calling party) is NON-ISDN.
The Gateway does NOT generate ring back towards the network side (PSTN or PABX), if the setup contains No Progress IE (Progress IE =0), meaning the originating address (calling party) is ISDN.
This is an example of when this might occur. International calls are arriving via the ISDN.
PSTN --------- IOS Gateway ------------ CallManager ------------ IP phone
A call from a NON-ISDN terminal is received. The setup contains a Progress IE = 3. The gateway generates the ring back when it receives the alert from the Cisco CallManager.
Note: These debugs were captured by issuing the debug isdn q931 Cisco IOS® Software command:
01:34:48: ISDN Se0:15: RX <- SETUP pd = 8 callref = 0x002B 01:34:48: Sending Complete 01:34:48: Bearer Capability i = 0x9090A3 01:34:48: Channel ID i = 0xA9838D 01:34:48: Progress Ind i = 0x8583 - Origination address is non-ISDN 01:34:48: Calling Party Number i = 0x2183, '27045000', Plan:ISDN, Type:National 01:34:48: Called Party Number i = 0xA1, '27182145', Plan:ISDN, Type:National 01:34:48: ISDN Se0:15: TX -> CALL_PROC pd = 8 callref = 0x802B 01:34:48: Channel ID i = 0xA9838D 01:34:48: act_alert: Tone Ring Back generated in direction Network One 01:34:48: act_gen_tone: Tone Ring Back generated in direction Network 01:34:48: ISDN Se0:15: TX -> ALERTING pd = 8 callref = 0x802B
A call is received from an ISDN terminal. There is no Progress IE in the setup. (Progress IE = 0). The Gateway is not generating ring back when it receives the alert from the Cisco CallManager.
01:37:01: ISDN Se0:15: RX <- SETUP pd = 8 callref = 0x002E 01:37:01: Sending Complete 01:37:01: Bearer Capability i = 0x8090A3 01:37:01: Channel ID i = 0xA98391 01:37:01: Calling Party Number i = 0x2183, '478681058', Plan:ISDN, Type:International 01:37:01: Called Party Number i = 0xA1, '27182145', Plan:ISDN, Type:International 01:37:01: High Layer Compat i = 0x9181 01:37:01: ISDN Se0:15: TX -> CALL_PROC pd = 8 callref = 0x802E 01:37:01: Channel ID i = 0xA98391 01:37:01: ISDN Se0:15: TX -> ALERTING pd = 8 callref = 0x802E
In this example, the gateway is expecting the ISDN to generate the ring back (due to no PI of 3). The ISDN, however, is not generating a ring back tone. This results in the caller only hearing silence until the called party answers the call. This may be due to an ISDN interworking issue caused because the call originated internationally (normally ring is generated at the terminating device for international calls).
You can force the gateway to generate a ring back by issuing the progress_ind setup enable 3 command. Configure this on the VoIP pointing to the Cisco CallManager.
! dial-peer voice 500 voip destination-pattern 5... progress_ind setup enable 3 !-- Forces ring back tone for this peer. session target ipv4:10.200.73.15 codec g711ulaw !
Note: In case of multiple VoIP peers that can be matched, make sure to configure this on all of them.
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