How can I create database link from Oracle to Sybase (SAP)?

Question

How can I create database link from Oracle to Sybase (SAP)? localhost..

CREATE PUBLIC DATABASE LINK "SAP_TEST"
 CONNECT TO sa
 IDENTIFIED BY SAPPROD
 USING 'host:port/master';

this way not working

My Error :

ORA-12537: TNS:connection closed

CREATE PUBLIC DATABASE LINK "SAP_TEST"
 CONNECT TO sa
 IDENTIFIED BY SAPPROD
 USING 'host:port/master';