sometime Our call established successfully, some unsuccessfully between Lync and Skype; when unsuccessful, it shows "Bacike wang is unavailable or may be offline", How I will fix it?

Thanks!

From the diagnostic got below logs:

Did this happen to the same user?

Did you gateway support SIP REFER? If it supports SIP REFER, you need to enable refer support in Lync Control Panel. If it doesnt, you should uncheck the option.

Please check the dialed phone number was formatted correctly.

Yes, it happen to other same users. when we call to Skype from Lync, or to Lync from Skype.

what the gateway you mentioned is ? mediation server? Audio gateway? our Lync 2013 server is STD.

How to check SIP REFER?

If we call Skype users, whether the call Skpye is relative with Dial plan?

Sorry, I misunderstood you.

You just made an audio call between Lync users and Skype users, right?

Would you provide a more detailed log file?

Please check if you can find any error in the event view log on your Lync edge server.

Yes, i made a audio call between Lync and Skype.

how i will provide to you? by email? what logs you need?

On edge server, i not found any error logs from Event Logs.