diff --git a/doc/epp/contact.md b/doc/epp/contact.md
index a1959310a..64f3fc056 100644
--- a/doc/epp/contact.md
+++ b/doc/epp/contact.md
@@ -1,5 +1,8 @@
 ## Contact related functions
 
+Please study Cantact Mapping protocol:
+http://tools.ietf.org/html/rfc5733
+
 ### Contact create
 
     Field name                 Min-max  Field description