why ldap_simple_bind() can't return immediately?

hii: i have call ldap_simple_bind() function but it will return for a long time(almost 60 seconds, and i am working in linux redhat as 4, openldap2.2), but the man doc says this is a asyschronized function, any option should i set the pLdapConnection?

if ((msgid = ldap_simple_bind(pLdapConnection, pUserDN, pPassword)) == -1) /*ldap_simple_bind() return for 60 seconds if the server wrong or down.*/ ... ... ret = ldap_result(pLdapConnection, msgid, LDAP_MSG_ALL, & tv_select_timeout, &result);