Navigation: Network Configuration -> Global
1. Check ‘Enable media bypass’ in Global setting.
2. Confirm you have also disabled media bypass in the trunk configuration
Figure 14: Media Bypass
Configure RTCP, Session Timer through the Windows PowerShell® command line interface because they are not configurable on Lync Server Control Panel
1. RTCPCallsonHold and RTCPActiveCalls must be turned off. RTCP is a control channel that is opened and is used to monitor the network specific conditions of the RTP channel. As REFER is disabled and Media Bypass is enabled on ISR Trunk, RTCP should be disabled on Lync Server.
Set-CsTrunkConfiguration –identity <Trunk name> –RTCPActiveCalls $false –RTCPCallsonHold $false
2. SessionTimer must be enabled. Because the RTCP channel is disabled, session timers must be enabled so that calls don’t stay up indefinitely in case we don’t get proper teardown of the call.
Set-CsTrunkConfiguration –identity <Trunk name> –EnableSessionTimer $true
3. Media EncryptionLevel must be set to SupportEncryption. Since we do not support SRTP to Cisco through Direct SIP, we need to set the media configuration’s EncryptionLevel to SupportEncryption so that SRTP will only be used if it can be negotiated. By default, this parameter is set to RequireEncryption, meaning SRTP must be used.
Set-CsMediaConfiguration –identity Global -EncryptionLevel SupportEncryption
 Host Name
 Domain Name
 IP Address of DNS Server
 List of supported codecs in the order of preference
 This is an example of the configuration required to enable call hold on Analog Endpoints. To make this active you must enter “service dsapp” in the voice dialpeer.
 PRI interface on ISR Gateway
 Dial peer for all calls going out to Lync
 Dial peer for calls starting with +1 going out to PRI
 Dial peer for analog port
 Dial peer for calls to an Analog extension with 9728522617
 Dial peer for calls to an Analog extension with 9728522618
 Dial peer for calls going out to Lync with destination pattern 972852263.
 Block 183 without sdp
 Dial peer for calls going out from Analog extensions