You have a NAT issue.
When you make a SIP call, there is an exchange of messages to establish the call and each request is usually answered with a response. When the initial INVITE is sent, it starts a timer (T1) which is used by the device that sent the INVITE to wait for an ACK from the receiving device at which point if received, the call is considered established and the call will proceed normally. If the ACK is not seen, then at the end of T1, timer B kicks in and disconnects the call and this time is 32 seconds.
This is usually because one end is telling the other end to use its private IP rather than its public IP and as a result, the ACK that is sent is never seen and the call is disconnected.
Presumably you have set PBX settings, SIP settings, External IP. Host to have the public IP or public FQDN and you have checked the SDP box as well as having included the local LAN into the settings as the bottom of the page?
Additionally, at the remote site/phones, you have set the public IP in the NAT IP area (phone make and model unknown) so that when they communicate they are telling the PBX what public IP to use? There may be more to it than this as we do not know anything about the remote - how many extension behind a firewall, dynamic or static IP, port forwarding, SIP ALG, etc.
Check the UCM first and then advise on the other remote aspects with more detail.