What should you check?

Your customer’s company has a main office and five branch offices located in different cities. Your
customer has a Microsoft Lync Server 2013 datacenter configured with Enterprise Voice at the main
office. The customer has deployed a Survivable Branch Appliance (SBA) at the first branch office and
connected it to a public switched telephone network (PSTN) by using a Tl trunk line provided by your
service provider. The gateway is configured to use fully qualified domain names (FQDNs). All
functionality has been tested by using pilot users at the branch office. The customer reports that
they tested branch isolation by disconnecting the wide area network (WAN) from their branch office
and making an outbound call. The call was successful. Next, they made an inbound call to the branch
office and the call failed. To troubleshoot the issue, you begin a trace of IncomingAndOutgoingCalls
by using centralized logging, and make an inbound call. You open the log in snooper and search for
incoming calls with the phone number from which you are calling. You do not find any messages.
You open the syslog from the gateway side of the SBA and discover that messages are sent to the
Lync Mediation server pool, but no responses have been received. You connect the WAN from the
branch office and make an inbound call. The call is successful. Your investigation suggests that there
is a configuration error on the Gateway side of the SBA. You need to identify the configuration error
that causes inbound calls to fail. What should you check?