OpenLdap Protocol - 10 hours

[ldap@mm.st]

I have RH5 systems that authenticate against stock RH5 Openldap servers
(2.3.43).   System files (ldap.conf, pam files etc) are setup to contact
the openldap server using tls.  When a system boots up some of the
system daemons (ntpd, hald, dbus-daemon) establish an ldap connection
the the server.  Once these connections get established they seem to
never go away which is fine I guess.   
So what I have is a persistent tcp connections like this:

client:51520 -->  openldapServer:389

I'm trying to work through some firewall issues and I have noticed that
the ldap server sends a "ack" packet to the client every 10 hours
without fail via these sockets that the daemons spawned.  This is sent
from the server without any thing from the client first.  The 10 hours
is very consistent.   Does anyone know if there is something in the ldap
protocol or slapd that would cause this behavior?  Just trying to rule
things out.

openldapServer:389 --> client:51520