To check whether your Skype-to-Skype call is being relayed:

1. If you are using Skype 5.1 or lower:
   1. In the menu bar, click Tools > Options > Advanced > Connection.
   2. Tick Display technical call info during calls and click Save.
2. Make a Skype-to-Skype call.
3. In the menu bar, click Call > Call Technical Info.
4. A box with technical information related to the call will be displayed. If the call is relayed, the word next to SessionOut and SessionIn will be RELAY_UDP or RELAY_TCP.

If the call is relayed, you cannot make HD video calls.