PROBLEM:
Users hear an echo when making a call using Skype for Business either as a published app or published desktop with HDX Real Time Optimization Pack 2.1 - 2.7

SCENARIO: 

• User A from Site 1 makes a call using published app Skype from Polycom phone (Headset) to User B at Site 2.
• Audio is fine on both ends.
• User A then places the call on Speaker on Polycom phone and User B from Site 2 can hear User B's own echo when speaking.
• User A does not hear echo from their end. 
• This Polycom phone does have Acoustic Echo Cancellation feature. The echo can be heard if the call starts out with speaker instead of headset. The customer does not experience this issue when using Skype on local machine bypassing Citrix.
• Also, he tested this with another device (Windows Laptop) with built-in mic. The laptop was also experiencing the echo issue during a Skype call using Citrix.

This is a known limitation in versions up to 2.7. Although Citrix RTME contains some functionality for Echo Cancellation this feature is being constantly improved for increased coverage of various use-cases.

Citrix has introduced a new echo cancellation library (AEC3) in RTME 2.8 for Windows which provides the highest levels of echo removal.


WORKAROUND for older RTME versions up to 2.7:
At this time using a headset is highly recommended, especially in noisy environments.
When speakerphone functionality is needed, use Microsoft-certified USB speakerphones with built-in Acoustic Echo Cancellation (AEC)
Here is a list of SfB qualified devices http://partnersolutions.skypeforbusiness.com/solutionscatalog
If using PC speakers, place them as far as possible from the microphone and from any surfaces that may reflect the sound into the microphone