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

Mon Jun 3 22:31:37 EDT 2024

Hi Nathan

Thank you for your analysis & especially your “Hmm, maybe with scenario #2”, - roaming off Wi-Fi on to cellular ..

I thought this might be of interest to the community as there are only so many Wireless IMS Network operators & UC/CCaaS apps are so popular, this might be a systematic problem of wider interest.

these iPhone-originated calls are made by a vendor UC/CCaaS app over standard VoLTE/IMS Network via our ITSP softswitch/feature svr (same vendor as the UC App) our UCaaS core. It might be internet on the access/mobile side (as you say Wi-Fi) but its the carrier's IMS core/private network to us.

It is NAT & IPv4

Many Thanks & Best Regards,

For your convenience, please click here<https://calendly.com/richard-406/30min> to schedule a time for us to talk.

Richard Jobson
Teraquant Corporation
ph: 719 488 1003
d/l: (719) 766-8523
www.teraquant.com<http://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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From: VoiceOps <voiceops-bounces at voiceops.org> on behalf of Nathan Anderson via VoiceOps <voiceops at voiceops.org>
Date: Monday, June 3, 2024 at 6:46 PM
To: voiceops at voiceops.org <voiceops at voiceops.org>
Subject: Re: [VoiceOps] Has anyone seen this? Voice UCaaS application on iPhone generated call: switching source IP address mid-call with no SIP signaling to indicate
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 discover 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 [though that might be difficult in the case where it *started* on WiFi & the WiFi network disappeared / moved out of range], 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<https://calendly.com/richard-406/30min> to schedule a time for us to talk.

Richard Jobson
Teraquant Corporation
ph: 719 488 1003
d/l: (719) 766-8523
www.teraquant.com<http://www.teraquant.com/>
richard at teraquant.com<mailto: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.

--
NOTICE: This electronic mail transmission may contain confidential information and is intended only for the person(s) named. Any use, copying, or disclosure by any other person is strictly prohibited. If you have received this transmission in error, please notify the sender via e-mail.

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