Thank wonsa03 for your reply.
but we are not using any relay state parameter in SP->IdP partnership, also we have Idle timeout set as 2hrs. so we can wipe out the idea of having timeout issue, since redirection is happening sometimes in 1 min as well, so don't think issue of timeout.
I also observed that during the redirection in SSO service URL it tries to set two fedSESSION cookie in browser (.abc.com and abc.com ) and in ACO we have defined cookie domain=.abc.com so only one cookie has to be set with .abc.com
could this be fedSESSION cookie conflict issue ?
Regards
Prashant