IP Phone SIP Calls Dropping or Delayed – Need Help Diagnosing | Community
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Pringlec
Newcomer
April 23, 2025
Question

IP Phone SIP Calls Dropping or Delayed – Need Help Diagnosing

  • April 23, 2025
  • 3 replies
  • 11 views

Hi everyone,
I'm currently troubleshooting a recurring issue with Zoom Phone/Poly IP phones where SIP calls are either delayed or dropped intermittently.

Details:

  • Phones: Poly CCX 500 and Edge E300 models

  • Call path: SIP calls via Zoom Phone

  • Some calls go straight to voicemail or drop without audio

  • Other times, there's a delay before the callee hears ringing

  • My own test calls to the same numbers go through fine

  • Problem seems intermittent and inconsistent

What I've Tried:

  • Enabled logging on the phones (set to Debug)

  • Captured traffic using SPAN on switch ports

  • Collected packet captures on both sides (caller & callee)

  • Noticed TLS sessions but traffic is encrypted (can't inspect payload)

  • Confirmed phones are updated and network is stable

Ask: Has anyone run into this issue before? Any tips for:

  • Decrypting or analyzing encrypted SIP/TLS traffic?

  • Zoom Phone-specific call signaling insights?

  • Additional logs or settings I should look into on Poly devices?

Happy to provide more details if needed — I’m just trying to figure out where the issue is happening (Zoom, network, or phones). Appreciate any guidance!

3 replies

sparrow
Community Super Champion | Customer
sparrow
Community Super Champion | Customer
April 24, 2025

What debug level modules did you enabled on the phone? Have you engaged your firewall team to capture SIP Logs on their side? 

P
Newcomer
PringlecAuthor
Newcomer
April 24, 2025

Thanks for the reply

 

For the debug logging, I set the Global Log Limit to Debug, and for the Module Log Level Limits, I specifically enabled Debug for the following modules:

Application

DNS

Network

SIP

SRTP

These modules seemed most relevant to the signaling and media handling issues we've been seeing.

As for the firewall side, yes — We have started capturing logs and packet data on the firewall. I have looked though our firewall settings and I do not see anything explicity blocking anything from zoom. We are also allowing traffic from all the ports they mention in their KBs. 

 

Its weird becacue this issue kind of came out of no where where as about almost a month ago everything was working fine and now all of a sudden there are tons of reported issues. 

 

We also have two other locations and the other two location have identical firewall rules and there is no reported issues with Zoom Phone.  

sparrow
Community Super Champion | Customer
sparrow
Community Super Champion | Customer
April 25, 2025

Are you running BYOC or you using Zoom as your PSTN access? Are you having the same issue with the Zoom app?

P
Newcomer
PringlecAuthor
Newcomer
April 25, 2025

Wea are using Zoom as PSTN. We do not have issues with Zoom App. 

E
Community Super Champion | Partner
Eliot
Community Super Champion | Partner
April 26, 2025

hi @Pringlec 

 

new hp/poly zoom edition firmware for ccx and edge e series dated 3/16/2025 addressed a number of issues.  I have an e450 that was intermittently losing network connection.  I did a factory reset which automatically updated the firmware.  No more issues.

 

Current as of 4/26/2025 poly/zoom ccx firmware is 9.0.1.6562

Current as of 4/26/2025 poly/zoom edge e series firmware is 8.2.3.0870

Zoom Phone Certified Hardware

 

Did my response answer your question? If so, please don't forget to mark the reply as an accepted solution.

 

thanks,  eliot

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