Hello Vivek,
most probably (if your PC in LAN) your proxi server does nor permit outbound voice packets to go away, OR (if you have got stand-alone PC) your ISP does not allow outband voice packets. In VIVE manual you can read what ports have to be opened on proxi server to allow voice packets to go both ways. If the problem with ISP – it is difficult to find the solution.
Sergey Starik