Pastebins of just the sip are rarely useful, if you want to pastebin something useful try posting the debug log from freeswitch on pastebin.freeswitch.org. Also editing out information only serves to possibly mask the underlying issue.

The IPs of your SIP servers (if they are on public IPs) are already well known to the sip scanners, it only took them about an hour to find your boxes once you turned it on)

From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of devang nathwani
Sent: Thursday, December 8, 2016 8:54 AM
To: FreeSWITCH Users Help <freeswitch-users@lists.freeswitch.org>
Subject: [Freeswitch-users] 503 service unavailable

Hello,

working one:
http://pastebin.com/ncyxUQj8

nonworking one with 503 service unavailable
http://pastebin.com/w7A689Bu

Here i have two scenarios, first is configured with Provider(1), this call routed and established successfully.

the second is configured with Provider(2), with this one freeswitch sending 503 event before routing the call to Provider(2)

so why 503?

- Devang.