Have you looked at a debug log when this is happening to see what FreeSWITCH thinks is going on?

On Oct 27, 2016, at 7:14 AM, devang nathwani <devang.nathwani31589@gmail.com> wrote:

Hello,

Freeswitch version: 1.6.11
Number of registration on my switch: 270+
Ram: 4 GB, 1 GB is free; 64 bit debian 8

I am facing this issue, where some time i am getting continuous INVITE registration requests but freeswitch not responding to it

and sometime i am getting 503 service unavailable

I have gone though https://freeswitch.org/jira/si/jira.issueviews:issue-html/FS-6589/FS-6589.html as well but not finding much helpful.

here is the sip log for the same, if you want to go through.
http://pastebin.com/PXz277XD

Is RAM upgrade a solution? or any other?