Teleworker keeps dropping

[pen-nerd]

I am setting up teleworkers with various Mitel 5220 and 5330 phones.  At all locations I am successful at connecting the teleworker sets to the MBG.  I can make and receive calls.  However, if a call is not in session, the phones will disconnect after 25 -30 seconds and remain disconnected for 45 - 50 seconds.  They don't appear to be rebooting.  On my newest phones, they actually show the network icon go from Green to White with an orange "!".  After they stay disconnected for 45-50 seconds, they connect back up and you can make and receive calls again for another 25-30 seconds.

I thought maybe the firewall was blocking some sort of traffic, but I built a wide open rule between one remote site and the MBG with the same result.

Wireshark at the phone site shows several TCP retransmissions from the phone that accompany each outage.

I'm completely at a loss on where to look next.  Is there a keepalive packet that I could have misconfigured or something? 
I could really use some help getting this set up so my coworkers can work from home a little better.

I greatly appreciate any guidance anyone can offer.

Thanks,
Bill

[johnp]

Is the MBG clustered?

[pen-nerd]

Thanks for the reply Johnp. Yes it is.  It is clustered with another micollab server as would be done in a DMZ except all three servers are in the LAN subnet with holes in the firewall to the Micollab UC server and the Micollab BG server.  I get the same results whether I connect to the BG or the UC server.
 
****************
*  Micollab BG - \   *
*                        --*--  Firewall --- Cloud
*  Micollab UC - /   *
*       |                  *
*  Mitel 3300         *
****************

[johnp]

I assume that these are in different zones. Verify that they are set to use the default MBG zone, I would also enabled ping before redirect. I had this happening last week for a customer who had users set to lan zone and after changing them and adding the option no issues

[pen-nerd]

Thanks for your help Johnp.  The MBG servers are indeed in separate zones.

The Default zone is empty
Outside zone (backup zone is Inside zone) = UC server
Inside zone  (backup zone is Outside zone) = BG server

Are you saying that the teleworker client needs to be set to use the inside zone?
Or that I need to move the BG server into the Default Zone and have users pointed there?

And lastly, I'm not finding how to set the teleworker to a zone unless you mean setting the teleworker IP address when you boot the phone.
I certainly appreciate your assistance.  Sorry to be so unknowledgeable.  I've never been this deep into phones before and it is straining my knowledge.

Thank you,
Bill

[johnp]

Should be set to outside zone

[pen-nerd]

Thanks johnp!  Enabling Ping before Redirect did the trick.  The other settings were already as you indicated.  Now my remote help desk will have their phones ringing non-stop.  But at least it will reduce the number of voicemails they get.  You really helped us out.

Bill