PL/SQL :: How To Get Client Machine Name And Client User Name

the trigger shown below is working fine.But i want to get client machine name and client osuser name in the output of the same trigger shown below,how can i achieve this in the same trigger?

trigger :
------------
CREATE TABLE logonaudit
(
user_id VARCHAR2(30),
sess_id NUMBER(10),
logon_time DATE,
host VARCHAR2(20));

[code]....

the output showing sessionid,date,db user name,host as local server machine name.but i want client machine name and client osuser names as u all know clients login to database from their machines.