title: NSUUID duplication chance form different device.
body: <p>I need to generate Unique ID for the device when the application installed, and store this value on the device, then need to communicate with server using this UUID. And it seems <a href="https://developer.apple.com/library/prerelease/ios/documentation/Foundation/Reference/NSUUID_Class/index.html" rel="nofollow noreferrer">NSSUUD</a> suit for the sitiation, but I am confused is there any chance of duplication of the UUID from multiple device. I already found the answer <a href="https://stackoverflow.com/a/6963990/1573209">https://stackoverflow.com/a/6963990/1573209</a> where it describe that the version 1 type uses MAC address and 60 bit clock to generate UUID, so the duplication chance is negligible. Where as the Version4 uses some fixed number and some random number to generate the UUID, and the <a href="https://developer.apple.com/library/prerelease/ios/documentation/Foundation/Reference/NSUUID_Class/index.html" rel="nofollow noreferrer">doc</a> says that <code>UUIDs created by NSUUID conform to RFC 4122 version 4 and are created with random bytes</code></p>
  
  <p>Does that mean the chance of duplication higher?.
  Then how can I use version 1 type of UUID generator, I cant see any documentation for it. </p>