Teams outgoing call via direct routing don't work intermittently

[mrvoipstuff]

Hi. 

We are getting an intermittent issue with some of our outgoing calls where they don't seem to work .. it rings out and we get 180 ringing back but soon after there's a RE-INVITE from far end followed by 488 Media not acceptable from MS Teams. I've attached SIP ladder diagram. 

calls to most outgoing numbers work but there are some that just wouldn't work and throw 488 error. 

using a direct routing setup . call flow goes like this 

Teams phone client => Teams phone system => SBC (Cisco) => ITSP

appreciate any insight into this please. 

[#2]

@mrvoipstuff 

I can't view your diagram due to our download rules, but this definitely feels like an SBC configuration issue.

Look at the third item on MS page about a 488 SIP error.

SIP 488 and Microsoft response codes - Microsoft Teams | Microsoft Learn

We had to make a change to use ICE lite correctly. It has been a while since we made that change and I don't recalled exactly what we changed.