[VoiceOps] Has anyone seen this? Voice UCaaS application on iPhone generated call: switching source IP address mid-call with no SIP signaling to indicate

[Nathan Anderson]

Slightly confused (based on your references to "Wireless IMS Network SBC")
whether these iPhone-originated calls are just standard VoLTE/IMS calls being
made by the native phone app and being carried by the carrier's IMS core, or
whether these are SIP calls being sent to your own UCaaS core by your app over
the carrier's regular internet/data APN.

 

If you are saying that you have direct-IP voice peering with one or more
wireless carriers, and that iPhone users on those networks are calling numbers
of yours & you are seeing the source IP of RTP traffic change mid-call, then I
don't see how that can be anything *but* a carrier issue.  That said, I also
don't see how that can be an iPhone-specific problem, either, or how you
managed to arrive at that conclusion.  If you were to more closely look at logs
related to calls where this is happening, I'd expect that you would find that
1) the problem is specific to a particular carrier, not a particular phone
model, and 2) you'll find many calls coming from that one carrier across
multiple phone models exhibiting the issue.  As to WHY the carrier might be
doing this...I haven't the foggiest.

 

If you are saying you have iPhone users running an app of yours that is making
outgoing SIP calls directly through your ITSP network over the carrier's
internet APN, then ...I don't see how that could be anything but a carrier
issue, either, honestly.  You didn't mention whether this was IPv4 or IPv6
though.  I'd be surprised if you saw this happening when the traffic is
arriving to you via IPv6.  However, for IPv4 traffic, it would not surprise me.
  Vast majority of carriers in the U.S. are handing out RFC1918 space IP
addresses to end-user devices & putting them behind a masquerading NAT.  You'd
expect that the NAT would try to retain the same source IP for the duration of
a given session, but I would not be shocked to hear that the NAT configuration
or the NAT engine itself is broken in some way, leading to this symptom.  (I'd
also not be surprised to learn that the carriers simply couldn't care less if
SIP traffic over the internet to their subscribers is unreliable, even though
they've largely gotten to the point where voice services are no longer their
primary money-maker...industry inertia and all that.)  If you don't already
have your own ITSP service natively reachable over IPv6 yet, you might consider
finally getting around to doing so...most of the major mobile carriers in the
U.S. are dual-stacking these days, so if carrier-side IPv4 NAT is the cause,
this would work around it for vast majority of users I'd think.

 

Maybe you are trying to describe a different scenario than either of these, but
I'm having trouble coming up with another one.  And in either case, I'm
confused how you narrowed it down to iPhones, and not to a particular carrier?

 

(Hmm, maybe with scenario #2, is it possible the customer's phone is moving
between the mobile data network and a local WiFi network while in the middle of
a call?  You'd hope the phone would be smart enough to either keep the existing
session on the same network interface that it began on, or at least properly
notify the app that the network interface is changing, in which case the app
could have a fighting chance of getting a re-INVITE sent out?  If you look at
the source IPs involved, are they always the carrier's IPs, or are you seeing
the traffic move between completely unrelated networks/ASes?)

 

-- Nathan

 

From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Richard
Jobson via VoiceOps
Sent: Monday, June 3, 2024 11:08 AM
To: voiceops at voiceops.org
Subject: [VoiceOps] Has anyone seen this? Voice UCaaS application on iPhone
generated call: switching source IP address mid-call with no SIP signaling to
indicate

 

Just curious as to whether the community thinks this is a network configuration
issue or a Mobile app issue

 

 

This is either …


1.        Something to do with the app on the iPhone

2.       Or is the Wireless IMS Network SBC that is changing the srce IP Addr
mid-call

3.            Or RTP has been routed to a different Wireless IMS Network SBC
mid-call

 

this behavior is totally noncompliant to the RFC.

 

The Oracle SBC in our ITSP network maintains the call up because the SSRC
remains the same. However, when this happens, a second or third time it gets
complicated .

 

Many Thanks & Best Regards,

 

For your convenience, please click here to schedule a time for us to talk.

 

Richard Jobson

Teraquant Corporation

ph: 719 488 1003

d/l: (719) 766-8523

www.teraquant.com

richard at teraquant.com

https://www.linkedin.com/in/uc-expert-monitoring/

 

Network Monitoring and Service Assurance - Speech Quality Experts (PESQ/POLQA)
and Active Testing - Reporting – HPBX - Session Border Controllers – SASE and
SD-WAN - Big Data Analytics, fraud detection and protection. 

 

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