We have seen an issue on a customers site (as well as our own kit) with the MBG being blacklisted by the PBX, we are probably going to get this a lot more with the number of remote 6900/softphones in the current environment (affects all SIP devices through the MBG).
The phone system will blacklist an IP address if the number of SIP requests exceeds a pre-configure threshold on the phone system. When people are using the MBG, all the SIP traffic is coming from a single IP address so this threshold is easily reached. We have around 25 remote phones and it has happened to us twice. They may also see 112 alarms on the PBX and system slow down.
When black listed, remote phones will go offline.
If customers are using an MBG we are going to recommend they turn of the admission control. Hopefully Mitel will add a method to White list the MBG IP address in the next service pack.
How to disable:
Could you please disable Admission Control feature in DBP under Online Monitor mode ("System"
>"Devices and Feature Codes">"SIP Peers"->"General Configuration", set "Enable Admission Control" flag to No)?