I have tried different settings in the profile for the failing carrier but no luck. I assume its a series of changes to get it to work. Looks like we sare sending the carrier a 183 and they send back a blank 180
Could you share a call trace or signaling trace from both sides — on the carrier leg and on your side? That is usually the best way to confirm whether this is a carrier behavior issue or something being altered by the local profile.
From a SIP perspective, 180 Ringing means the called side is being alerted, and the caller side may generate local ringback based on that response. In RFC 3261, 180 is specifically associated with alerting, and the UAC may use it to start local ringback. ()
By contrast, 183 Session Progress is a more generic provisional response used to convey call progress information. In practice, it is commonly associated with early media, especially when SDP is present. In PSTN interworking examples, RFC 3666 explicitly notes that 183 can indicate that in-band alerting may flow from the called side toward the caller. ()
So, if the carrier is sending a 180 without SDP, that normally means there is no early media being provided by the carrier, and the originating side is expected to generate ringback locally. If the originating endpoint does not generate local ringback in that scenario, the result can be exactly what you are hearing: silence until a later response or the final 200 OK. ()
As an additional consideration, ProSBC has profile options that can convert 180 to 183 and vice versa, and it may also be configured to ignore or attempt to generate SDP locally. If those options are set incorrectly, they can also lead to the “silent call before 200 OK” behavior you described.
In general, the safest approach is not to alter the signaling received from the carrier, and instead forward it unchanged. Modifying 180/183 behavior or trying to generate local media handling can create side effects unless you have a transcoding device installed and properly configured to handle the media path locally.
Without transcoding, the preferred behavior is usually to keep the signaling as received and let the endpoint or carrier handle ringback/early media in the standard way.
So before changing more profile flags, I would strongly recommend checking:
-
what the carrier is actually sending on its leg,
-
what ProSBC forwards to the calling side,
-
whether the calling endpoint expects local ringback on 180, or early media on 183/SDP.
Hi,
I recall having a similar issue, on one of our peers, don’t remember if exactly why this was the case, but I remember disabling PRACK in the SDP profile for that peer, did the trick.
You can try that and see if that works for you.
I tried dissabling PRACK, same issue. A 1/4 ring then dead air until the other side picks up
Cant seem to attach files here…
Andrew
| Time: | 2026/04/22 15:55:49.588 |
|---|---|
| undefined | ---- |
INVITE
=>
| undefined | ---- | ---- |
call-id 637457a21941b3fa6d3076fc58b559bc@173.237.220.133:5080
| undefined | ---- |
SIP UDP message remote=173.237.220.130:5060 → local=173.237.220.138:5060
| undefined | ---- |
v=0
o=- 1647461991 1647461991 IN IP4 173.237.220.130
s=-
c=IN IP4 173.237.220.130
t=0 0
m=audio 17600 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
| undefined | ---- |
MappingId=0xfff632a5 Session=0x0009cd5a
| undefined | ---- |
Call mode: Voice [Profile=DEFAULT]
| undefined | ---- |
Calling ‘14164520000’ NOA=UNSPECIFIED NPI=NPI_UNSPECIFIED / Called ‘16478314445’ NOA=UNSPECIFIED NPI=NPI_UNSPECIFIED
| undefined | ---- |
0.038s
| undefined | ---- | ---- | ---- | ---- |
Routing: [SrcNap=PBX2020, Calling=14164520000, Called=16478314445] found 3 matching routes: PBX2020_Outbound1, PBX2020_Outbound2, PBX2020_Outbound3
| undefined | ---- |
0.039s
| undefined | ---- | ---- | ---- | ---- |
Call mode: Voice [Profile=CONVERGIA]
| undefined | ---- |
=>
INVITE
SIP UDP message local=173.237.220.138:5060 → remote=204.10.207.104:5060
| undefined | ---- |
v=0
o=- 512494 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10002 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
MappingId=0xffb90f4f Session=0x0046f0b0
| undefined | ---- |
Init outgoing: Outgoing call (route 1/3, contact 1/1): [DstNap=CONVERGIA_2026_MAIN, Calling=14164520000, Called=16478314445, PrivateAddress=14164520000] [Route=PBX2020_Outbound1] (Related to 0xDB2ABF6A)
| undefined | ---- |
0.060s
| undefined | ---- | ---- | ---- | ---- |
<=
100 Trying
call-id 021BFD871881400000077BA2@VOIP_TS
| undefined | ---- |
1.195s
| undefined | ---- | ---- | ---- | ---- |
<=
183 Progress
Endpoint info (local 173.237.220.138:10002 (0) remote 204.10.207.103:62076 (0) Media=PCMU (0x0))
| undefined | ---- |
1.196s
| undefined | ---- | ---- |
183 Progress
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
Endpoint info (local 173.237.220.138:10000 (0) remote 173.237.220.130:17600 (0) Media=PCMU (0x0))
| undefined | ---- |
1.197s
| undefined | ---- | ---- | ---- | ---- |
Join full-duplex with 0x5B2ABF7D
| undefined | ---- |
Endpoint alloc
| undefined | ---- |
Join full-duplex with 0xDB2ABF6A
| undefined | ---- |
1.299s
| undefined | ---- | ---- | ---- | ---- |
Endpoint alloc
| undefined | ---- |
1.300s
| undefined | ---- | ---- | ---- | ---- |
Connection alloc full-duplex with 0x5B2ABF7D
| undefined | ---- |
Endpoint modified
| undefined | ---- |
Connection alloc full-duplex with 0xDB2ABF6A
| undefined | ---- |
4.809s
| undefined | ---- | ---- | ---- | ---- |
<=
180 Ringing
4.810s
| undefined | ---- | ---- |
183 Progress
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
4.911s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
5.013s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
14.296s
| undefined | ---- | ---- | ---- | ---- |
<=
200 OK
v=0
o=- 552090 637208 IN IP4 204.10.207.103
s=-
c=IN IP4 204.10.207.103
t=0 0
m=audio 62076 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
14.399s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
14.400s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
200 OK
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
14.509s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
19.724s
| undefined | ---- | ---- | ---- | ---- |
Terminate with cause (200-TOOLPACK_NORMAL)
| undefined | ---- |
BYE
=>
| undefined | ---- |
19.725s
| undefined | ---- | ---- | ---- | ---- |
Final stats (NAP ‘PBX2020’): FromNetwork[ Rx=914 Err=0 ] ToNetwork[ Tx=441 Err=0 ] RTP-Voice+CN[ Tx=441 Rx=914 RxErr=0 ] RTP-Event[ Tx=0 Rx=0 ]
| undefined | ---- |
MOS: 4.3 codec ideal MOS 4.3, Network quality: 100%
remote 173.237.220.130:17600 ------ | ------ local 173.237.220.138:10000
------------------------------------- 4.3 (PCMU) --------------------->
<----------------------------------- 0.0 (PCMU) -----------------------
| undefined | ---- |
Connection freed full-duplex with 0x5B2ABF7D
| undefined | ---- |
Endpoint freed
| undefined | ---- |
200 OK
<=
| undefined | ---- | ---- |
Terminate with cause (200-TOOLPACK_NORMAL)
| undefined | ---- |
Connection freed full-duplex with 0xDB2ABF6A
| undefined | ---- |
Final stats (NAP ‘CONVERGIA_2026_MAIN’): FromNetwork[ Rx=447 Err=0 ] ToNetwork[ Tx=261 Err=0 ] RTP-Voice+CN[ Tx=260 Rx=447 RxErr=0 ] RTP-Event[ Tx=0 Rx=0 ]
| undefined | ---- |
MOS: 4.3 codec ideal MOS 4.3, Network quality: 100%
local 173.237.220.138:10002 ------ | ------ remote 204.10.207.103:62076
------------------------------------- 0.0 (PCMU) --------------------->
<----------------------------------- 4.3 (PCMU) -----------------------
| undefined | ---- |
Endpoint freed
| undefined | ---- |
=>
BYE
19.743s
| undefined | ---- | ---- | ---- | ---- |
Completed (200-TOOLPACK_NORMAL)
| undefined | ---- |
19.754s
| undefined | ---- | ---- | ---- | ---- |
<=
200 OK
2nd leg
| Time: | 2026/04/22 15:55:49.588 |
|---|---|
| undefined | ---- |
INVITE
=>
| undefined | ---- | ---- |
call-id 637457a21941b3fa6d3076fc58b559bc@173.237.220.133:5080
| undefined | ---- |
SIP UDP message remote=173.237.220.130:5060 → local=173.237.220.138:5060
| undefined | ---- |
v=0
o=- 1647461991 1647461991 IN IP4 173.237.220.130
s=-
c=IN IP4 173.237.220.130
t=0 0
m=audio 17600 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
| undefined | ---- |
MappingId=0xfff632a5 Session=0x0009cd5a
| undefined | ---- |
Call mode: Voice [Profile=DEFAULT]
| undefined | ---- |
Calling ‘14164520000’ NOA=UNSPECIFIED NPI=NPI_UNSPECIFIED / Called ‘16478314445’ NOA=UNSPECIFIED NPI=NPI_UNSPECIFIED
| undefined | ---- |
0.038s
| undefined | ---- | ---- | ---- | ---- |
Routing: [SrcNap=PBX2020, Calling=14164520000, Called=16478314445] found 3 matching routes: PBX2020_Outbound1, PBX2020_Outbound2, PBX2020_Outbound3
| undefined | ---- |
0.039s
| undefined | ---- | ---- | ---- | ---- |
Call mode: Voice [Profile=CONVERGIA]
| undefined | ---- |
=>
INVITE
SIP UDP message local=173.237.220.138:5060 → remote=204.10.207.104:5060
| undefined | ---- |
v=0
o=- 512494 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10002 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
MappingId=0xffb90f4f Session=0x0046f0b0
| undefined | ---- |
Init outgoing: Outgoing call (route 1/3, contact 1/1): [DstNap=CONVERGIA_2026_MAIN, Calling=14164520000, Called=16478314445, PrivateAddress=14164520000] [Route=PBX2020_Outbound1] (Related to 0xDB2ABF6A)
| undefined | ---- |
0.060s
| undefined | ---- | ---- | ---- | ---- |
<=
100 Trying
call-id 021BFD871881400000077BA2@VOIP_TS
| undefined | ---- |
1.195s
| undefined | ---- | ---- | ---- | ---- |
<=
183 Progress
Endpoint info (local 173.237.220.138:10002 (0) remote 204.10.207.103:62076 (0) Media=PCMU (0x0))
| undefined | ---- |
1.196s
| undefined | ---- | ---- |
183 Progress
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
Endpoint info (local 173.237.220.138:10000 (0) remote 173.237.220.130:17600 (0) Media=PCMU (0x0))
| undefined | ---- |
1.197s
| undefined | ---- | ---- | ---- | ---- |
Join full-duplex with 0xDB2ABF6A
| undefined | ---- |
Join full-duplex with 0x5B2ABF7D
| undefined | ---- |
Endpoint alloc
| undefined | ---- |
1.299s
| undefined | ---- | ---- | ---- | ---- |
Endpoint alloc
| undefined | ---- |
1.300s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Connection alloc full-duplex with 0xDB2ABF6A
| undefined | ---- |
Connection alloc full-duplex with 0x5B2ABF7D
| undefined | ---- |
4.809s
| undefined | ---- | ---- | ---- | ---- |
<=
180 Ringing
4.810s
| undefined | ---- | ---- |
183 Progress
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
4.911s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
5.013s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
14.296s
| undefined | ---- | ---- | ---- | ---- |
<=
200 OK
v=0
o=- 552090 637208 IN IP4 204.10.207.103
s=-
c=IN IP4 204.10.207.103
t=0 0
m=audio 62076 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
14.399s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
14.400s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
200 OK
<=
| undefined | ---- | ---- |
v=0
o=- 512493 1 IN IP4 173.237.220.138
s=-
c=IN IP4 173.237.220.138
t=0 0
m=audio 10000 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=ptime:20
| undefined | ---- |
14.509s
| undefined | ---- | ---- | ---- | ---- |
Endpoint modified
| undefined | ---- |
Endpoint modified
| undefined | ---- |
19.724s
| undefined | ---- | ---- | ---- | ---- |
Terminate with cause (200-TOOLPACK_NORMAL)
| undefined | ---- |
BYE
=>
| undefined | ---- |
19.725s
| undefined | ---- | ---- | ---- | ---- |
Terminate with cause (200-TOOLPACK_NORMAL)
| undefined | ---- |
Connection freed full-duplex with 0xDB2ABF6A
| undefined | ---- |
Final stats (NAP ‘CONVERGIA_2026_MAIN’): FromNetwork[ Rx=447 Err=0 ] ToNetwork[ Tx=261 Err=0 ] RTP-Voice+CN[ Tx=260 Rx=447 RxErr=0 ] RTP-Event[ Tx=0 Rx=0 ]
| undefined | ---- |
MOS: 4.3 codec ideal MOS 4.3, Network quality: 100%
local 173.237.220.138:10002 ------ | ------ remote 204.10.207.103:62076
------------------------------------- 0.0 (PCMU) --------------------->
<----------------------------------- 4.3 (PCMU) -----------------------
| undefined | ---- |
Endpoint freed
| undefined | ---- |
=>
BYE
Final stats (NAP ‘PBX2020’): FromNetwork[ Rx=914 Err=0 ] ToNetwork[ Tx=441 Err=0 ] RTP-Voice+CN[ Tx=441 Rx=914 RxErr=0 ] RTP-Event[ Tx=0 Rx=0 ]
| undefined | ---- |
MOS: 4.3 codec ideal MOS 4.3, Network quality: 100%
remote 173.237.220.130:17600 ------ | ------ local 173.237.220.138:10000
------------------------------------- 4.3 (PCMU) --------------------->
<----------------------------------- 0.0 (PCMU) -----------------------
| undefined | ---- |
Connection freed full-duplex with 0x5B2ABF7D
| undefined | ---- |
Endpoint freed
| undefined | ---- |
200 OK
<=
| undefined | ---- |
19.743s
| undefined | ---- | ---- | ---- | ---- |
Completed (200-TOOLPACK_NORMAL)
| undefined | ---- |
19.754s
| undefined | ---- | ---- | ---- | ---- |
<=
200 OK
Completed (200-TOOLPACK_NORMAL)
Hello,
The root cause from the call flow. The carrier sends a 183 with SDP (early media / ringback), then later sends a 180 Ringing with no SDP. When that blank 180 arrives, ProSBC stops sending the early media ringback to the caller but doesn’t properly signal ringing — resulting in dead air until the call is answered.
This is similar to a known carrier interop pattern. Try a “fix” on the carrier profile (CONVERGIA in this case):
Profile > VOIP > SIP > Forward SIP hold SDP direction mode → Force Inactive
This tells the engine to properly handle the transition from 183 early media to 180 ringing when the carrier sends 180 without SDP. No PRACK changes needed — the issue isn’t PRACK-related.
Thank you,
Dave