14.9.3.7. Define Trunk Configuration 
The next step is to assign the OpenScape 4000 gateway to a trunk associated
with a pool or a site as follows:
- On Skype for Business Server 2015 Control Panel click Voice Routing, and then click the Trunk Configuration tab.
- Click New, and depending on the scope of the policy you want to create, click Site Configuration or Pool Configuration.
- Select a pool or site for this trunk configuration.
- In the New Trunk Configuration dialog box, click OK.
- To commit your changes, click Commit, and then click Commit all.
INFO:
make sure that Enable Media bypass is disabled and Enable refer support
is set to “None”.
- To enable encryption select Required on Encryption support level drop down.
- To commit your changes, click Commit, and then click Commit all.