eG Monitoring
 

Measures reported by LSMediationSrvTest

The Mediation Server is considered the last point of contact for the Lync environment before communicating to the telephony world for audio communication, whether its ingress or egress VoIP calls to the Public Switched Telephone Network (PSTN) world. The Mediation Server is required for leveraging for inbound calls, outbound calls, and dial-in conferencing in a Lync 2013 environment.

The Mediation Server listens for calls from both the server and the gateway. To listen for calls from the server, it uses Session Initiation Protocol (SIP) listening ports. Typically, port 5070 is used for Transport Layer Security (TLS) traffic coming from the Lync server. To listen for calls from the gateway, it uses port 5067 for IP and PSTN traffic.

The Mediation Server is considered a Back-to-Back User Agent (B2BUA), which is responsible for handling communication between two endpoints in a SIP call. All SIP signaling will traverse through the Front End Server and Mediation Server when in route to a PSTN gateway. Only when media bypass is enabled will calls bypass the Mediation Server, which means that the calls go from the Lync 2013 client straight to the PSTN gateway. When there's a PSTN gateway device local to where the call is being made, organizations will typically enable the Lync environment for media bypass to avoid having the media traverse the WAN to make a call. This improves call quality because it reduces the chance for latency, jitter, and packet loss, which naturally occurs when a VoIP call travels through multiple hop points before the call reaches the endpoint receiving the call.

Some of the Mediation Server's key functions include:

  • Encrypting and decrypting Secure Real-Time Transport Protocol (SRTP) data on the Lync server side
  • Translating SIP over TCP to SIP over mutual TLS (MTLS)
  • Translating media streams between the Lync server and the gateway peer of the Mediation Server
Using the LSMediationSrvTest test, it is possible to figure out how many audio channels are enabled with Phase Shift Modulation quality reporting and how many calls actually failed due to heavy load as well as due to the unexpected interaction from the proxy.

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
AudioPSMRep Indicates the number of audio channels that are currently enabled with Phase Shift Modulation (PSM) quality reporting. Number A low value is desired for this measure. Calculating PSM may cause processing overhead which in turn may directly affect the performance of the server. Therefore, administrators need to keep a check on the number of audio channels for which PSM reporting is enabled.
FailCallsByProxy Indicates the number of calls that failed due to the unexpected interaction from proxy on the mediation server during the last measurement period. Number Ideally, the value of this measure should be zero.
MediaConFail Indicates the number of calls that failed when the media connectivity between the Mediation server and the remote endpoints could not be established. Number Ideally, the value of this measure should be zero.
CandidateMiss Indicates the number of times the media stack does not have media relay components. Number  
CallFailIndex Indicates the scaled index between zero and 100 that is related to all call failures due to Global Health Index as a heavy load. Number