Lync 2010 does not support SRTP Key Derivation. It is not enough to set the key derivation rate to zero, it must be disabled. If the flag KDR is shipped in the SIP SDP crypto field, then the call will not established. The Windows EventLog will show the following error: Source: LS Mediation Server EventID: … Lync 2010 SRTP Key Derivation weiterlesen