Connecting two freeradius server ?

Hello I use freeradius to authenticate Chillispot users using an Openldap backend , everything works like a charm :-) Another (friendly) site has quite the same configuration they do use freeradius too to authenticate their wi-fi users. Both sites have a permanent Internet access. Now is it possible for "my" daemon to "communicate" with another freeradius daemon which is running in another distant site to let all of our users ( my site + distant site ) authenticate transparently with their own site logins/passwds on the two sites ? Thank you. -- Frank Bonnet