If you are facing problem that your SDK manager is not showing all Packages in the list to download then do following settings in SDK Manager.
Open the SDK manager and go to Tools->Options and make settings as shown in below figure.
HTTP Proxy Server: www.google.com
(This URL may be different depending on your country as it is www.google.com.ch for China)
HTTP Proxy Port: 80
Also check the Force https://… sources to be fetched using http:// …
Finally, click on Close button to close the setting window. Then close the SDK Manager also and re-open it, you must be getting complete list of packages.