Scenario#41 – No Ringback tone from H323 Gateway going to SIP trunk

One of our customer reported an issue with ring back tone when calling their Contact center.

I made a test call and observed that as a caller when you call their main Contact center number all you hear is dead silence and then when agent picks up the phone you could hear them talk. There was no ring back tone and no automated messages before an agent picks up the call.

The call flow was something like this:

PSTN > ISDN30 > H323 Dial-peer > SIP Trunk > 3rd-party Contact Center Equipment

First I thought it could be the third-party equipment which was not sending back the ring back tone so I asked them to confirm this. They came back saying they are definitely sending ring back and there was no issue with their equipment.

Looking at Q931 debugs I could see ALERTING message with payload but wasn’t sure why there was no ring back.

The dial-peers were looking ok as well:

!

dial-peer voice 8500 voip
corlist outgoing CCM
description DC1CCM01
preference 1
destination-pattern 361[01].
progress_ind setup enable 3
progress_ind alert enable 8
session target ipv4:10.1.30.12
dtmf-relay h245-signal h245-alphanumeric
no vad

!

dial-peer voice 8501 voip
corlist outgoing CCM
description DC1CCM02 Cycos Ansage
preference 2
destination-pattern 361[01].
progress_ind setup enable 3
progress_ind alert enable 8
session target ipv4:10.1.30.13
dtmf-relay h245-signal h245-alphanumeric
no vad
!
I then decided to run some debugs to get a complete picture as to what is going wrong. These were the debugs I opened on the gateway:

debug voip ccapi inout
debug cch323 all
debug h225 asn1
debug h245 asn1
debug ip tcp trans
debug ccsip all

Collected debugs in the following manner:

Router(config)# service sequence
Router(config)# service timestamps debug datetime localtime msec
Router(config)# logging buffered 10000000 7
Router(config)# no logging con
Router(config)# no logging mon
Router(config)# voice iec syslog

Note: Please be very careful when you run the above debugs as these are processor intensive and make sure you are not logging monitor and console.

The debugs were massive but this is what I observed:

From Gateway traces I can see RINGBACK has definitely been sent to Gateway –

005302: *Aug 25 23:44:07.256: //-1/xxxxxxxxxxxx/H323/cch323_h225_receiver: Received msg of type ALERTIND_CHOSEN
005303: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/alert_ind: ====== PI = 0
005304: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/alert_ind: alert ind ie_bit_mask 0x1260, displayInfo
005305: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/alert_ind: delay H245 address in alert
005306: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/alert_ind: Call Manager detected
005307: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/cch323_h225_receiver: ALERTIND_CHOSEN: src address = 10.187.10.8; dest address = 10.1.30.12
005308: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/run_h225_sm: Received event H225_EV_ALERT_IND while at state H225_REQ_FS_CALLPROC
005309: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/cch323_get_embedded_obj_from_ccb: ccb=0x4715D7A0, tag=18, size=83
005310: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/cch323_get_embedded_obj_from_ccb: Extraction FAILED
005311: *Aug 25 23:44:07.256: //3610/D48C17148501/CCAPI/cc_api_set_called_ccm_detected:
CallInfo(called ccm detected=TRUE ccmVersion 3)
005312: *Aug 25 23:44:07.256: //3610/D48C17148501/CCAPI/cc_api_set_delay_xport:
CallInfo(delay xport=TRUE)
005313: *Aug 25 23:44:07.256: //3610/D48C17148501/CCAPI/cc_api_call_alert:
Interface=0x46B2BAA8, Progress Indication=NULL(0), Signal Indication=SIGNAL RINGBACK(1)
005314: *Aug 25 23:44:07.256: //3610/D48C17148501/CCAPI/cc_api_call_alert:
Call Entry(Retry Count=0, Responsed=TRUE)
005315: *Aug 25 23:44:07.256: //3610/D48C17148501/H323/cch323_h225_set_new_state: Changing from H225_REQ_FS_CALLPROC state to H225_REQ_FS_ALERT state
005316: *Aug 25 23:44:07.260: //3609/D48C17148501/CCAPI/ccCallAlert:
Progress Indication=INBAND(8), Signal Indication=SIGNAL RINGBACK(1)

Then ALERTING Signal shown in ISDN Q931 debug:

005331: *Aug 25 23:44:07.264: ISDN Se0/0/0:15 Q931: TX -> ALERTING pd = 8 callref = 0x803A

But then Observed this:

005332: *Aug 25 23:44:07.264: //3610/D48C17148501/H323/h323_open_rtp_stream: Media In-active notification object not attached to ccb
005333: *Aug 25 23:44:07.264: //3610/D48C17148501/H323/cch323_set_dtmf_iw_enabled: negotiated dtmf relay: 0, dtmf_iw_enabled: 0, dtmf_sccp_enabled: 0
005334: *Aug 25 23:44:07.264: //3610/D48C17148501/H323/cch323_caps_ind: gw_id=1
005335: *Aug 25 23:44:07.264: //3610/D48C17148501/H323/cch323_peer_caps_ind_common: Load DSP with Preferred codec(16) g729r8, Bytes=20
005336: *Aug 25 23:44:07.264: //3610/D48C17148501/H323/cch323_peer_caps_ind_common: Set DSP for dtmf-relay = CC_CAP_DTMF_RELAY_INBAND_VOICE
005337: *Aug 25 23:44:07.396: TCP0: ACK timeout timer expired
005338: *Aug 25 23:44:07.448: //-1/xxxxxxxxxxxx/H323/cch323_ct_main: SOCK 2 Event 0x1
005339: *Aug 25 23:44:07.448: //-1/xxxxxxxxxxxx/H323/cch323_gw_process_read_socket: owner_data=0x46DA9F30, len=53, msgPtr=0x475C62BC
005340: *Aug 25 23:44:07.448: //-1/xxxxxxxxxxxx/H323/cch323_gw_process_read_socket: Received msg for H.225

I was a bit surprised as to why G729 codec was negotiated when the whole path is G711. Even the SIP trunk was in all-G711 region.

Looking closely at dial-peers I found what was missing!! The VOIP dial-peers were missing the “Voice class codec 1” command which had G711 as priority 1 codec. As the command was not there, the call was matching dial-peer 0 and hence negotiating G729 codec. I added the command and the problem was solved. I can now hear ring back tone as well as all automated messages.

This is how it looks after I made the changes:

005935: *Aug 26 00:15:26.432: //3620/349708E58506/H323/h323_open_rtp_stream: Media In-active notification object not attached to ccb
005936: *Aug 26 00:15:26.432: //3620/349708E58506/H323/cch323_set_dtmf_iw_enabled: negotiated dtmf relay: 0, dtmf_iw_enabled: 0, dtmf_sccp_enabled: 0
005937: *Aug 26 00:15:26.432: //3620/349708E58506/H323/cch323_caps_ind: gw_id=1
005938: *Aug 26 00:15:26.432: //3620/349708E58506/H323/cch323_peer_caps_ind_common: Load DSP with Preferred codec(5) g711ulaw, Bytes=160
005939: *Aug 26 00:15:26.432: //3620/349708E58506/H323/cch323_peer_caps_ind_common: Set DSP for dtmf-relay = CC_CAP_DTMF_RELAY_INBAND_VOICE
005940: *Aug 26 00:15:26.568: TCP0: ACK timeout timer expired
005941: *Aug 26 00:15:26.620: //-1/xxxxxxxxxxxx/H323/cch323_ct_main: SOCK 2 Event 0x1
005942: *Aug 26 00:15:26.620: //-1/xxxxxxxxxxxx/H323/cch323_gw_process_read_socket: owner_data=0x46DAB900, len=53, msgPtr=0x475C5200
005943: *Aug 26 00:15:26.620: //-1/xxxxxxxxxxxx/H323/cch323_gw_process_read_socket: Received msg for H.225
005944: *Aug 26 00:15:26.620: H225.0 INCOMING ENCODE BUFFER::= 28501900060008914A0005003497A50DEE3911E19D37B87571A7872310800100
005945: *Aug 26 00:15:26.620:
005946: *Aug 26 00:15:26.620: H225.0 INCOMING PDU ::=

Most of the time problems like these are Codec or MRG related so it’s always a good idea to start checking your codecs first.

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4 thoughts on “Scenario#41 – No Ringback tone from H323 Gateway going to SIP trunk

  1. Hi Ash,

    Thanks very much for sharing your knowledge and experience,very useful.

    In the scenario above, I understand that the voice class codec command in dial-peer 8500 and 8501 absent which is what caused the issue with codec. But I am not sure how the call would have matched dial-peer 0 because voice-class codec is not present in dial-peer 8500 and 8501. Can you please advise.


    Looking closely at dial-peers I found what was missing!! The VOIP dial-peers were missing the “Voice class codec 1″ command which had G711 as priority 1 codec. As the command was not there, the call was matching dial-peer 0 and hence negotiating G729 codec. I added the command and the problem was solved. I can now hear ring back tone as well as all automated messages.

    Thanks,

    Sivaji

  2. Hi Ash,thabkyou very much for this forum. It is cery usefull what you are doing here. Keep sharing your experience!!
    E. H

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