We are seeing an increasing number of reports from customers who are using I-phones and have recently updated to IOS 11, that are unable to call businesses who have Avaya and or Cisco CPE’s. Below is a short non-technical description, in my words and a fix that can be implemented on customer CPE’s.

1. It appears that the data packet size has changed in the new upgrade and it appears that there is larger header information in those packets now.
2. This larger packet size is unreadable for Avaya phone systems that are using UDP (undefined Protocol) as they are not being able to put the packets back together upon receiving them.

The Fix is to change the CPE/Phone system to use TCP instead of UDP. Once done, regardless of the 4G or 3G setting, calls should work.