Lync 2010 VOIP Media Bypass and External PSTN SIP Trunk Provider

    Lync Server 2010 Sip Trunk can support media bypass when the following options are considered.  Check with your  ITSP SIP Trunk provider for support on the following:

    • Refer (Optional)
    • SRTP (over g.711)
    • RTCPActiveCalls
    • RTCPCallsOnHold
    • EnableSessionTimer
    • Value for the maximum number of early dialogs that the gateway, PBX, or SBC can accept.
    • Verify ITSP to determine whether its SBC accepts media traffic directly from Lync Server 2010 endpoints.

    TechNet Details:

    • A Mediation Server peer must support the necessary capabilities for media bypass, the most important being the ability to handle multiple forked responses (known as “early dialogs”). Contact the manufacturer of your gateway or PBX, or your ITSP, to obtain the value for the maximum number of early dialogs that the gateway, PBX, or SBC can accept.
    • The Mediation Server peer must accept media traffic directly from Lync Server 2010 endpoints. Many ITSPs allow their SBC to receive traffic only from the Mediation Server. Contact your ITSP to determine whether its SBC accepts media traffic directly from Lync Server 2010 endpoints.
    • Lync Server 2010 clients and a Mediation Server peer must be well connected, meaning that they are either located in the same network region or at network sites that connect to the region over WAN links that have no bandwidth constraints
    • Select the Centralized media processing check box if there is a well-known media termination point (for example, a PSTN gateway where the media termination has the same IP as the signaling termination). Media bypass is only supported if this option is selected.
    • Important Refer Support Options (Refer Support is Recommended, but can be configured if enabled). If the trunk peer supports receiving SIP REFER requests from the Mediation Server, select the Enable refer support check box. Clear the check box if the trunk peer does not support receiving SIP REFER requests from the Mediation Server.

     

    Note: If your gateway does not support Refer.

    If you disable this option while the Enable media bypass option is selected, additional settings are required. If the trunk peer does not support receiving SIP REFER requests from the Mediation Server and media bypass is enabled, you must also run the Set-CsTrunkConfiguration cmdlet to disable RTCP for active and held calls in order to support proper conditions for media bypass. For details, see the Lync Server Management Shell documentation.Sample (No Refer Support, No SRTP Support)

    New-CsTrunkConfiguration -Identity site

    -EnableBypass $True -RTCPActiveCalls $False –RTCPCallsOnHold –RTPMode

    Set-CSMediaconfiguration –identity global –encryptionlevel supportencryption

    New-CsTrunkConfiguration Options · 

    RTCPActiveCalls

    This parameter determines whether RTCP packets are sent from the PSTN gateway, IP-PBX, or SBC at the service provider for active calls. An active call in this context is a call where media is allowed to flow in at least one direction. If RTCPActiveCalls is set to True, the Mediation Server or Lync Server client can terminate a call if it does not receive RTCP packets for a period exceeding 30 seconds.

    Note that disabling the checks for received RTCP media for active calls in Lync Server elements removes an important safeguard for detecting a dropped peer and should be done only if necessary.

    Default: True, must be set to False without Refer Support with Media Bypass · 

    RTCPCallsOnHold

    This parameter determines whether RTCP packets continue to be sent across the trunk for calls that have been placed on hold and no media packets are expected to flow in either direction. If Music on Hold is enabled at either the Lync Server client or the trunk, the call will be considered to be active and this property will be ignored. In these circumstances use the RTCPActiveCalls parameter.

    Note that disabling the checks for received RTCP media for active calls in Lync Server elements removes an important safeguard for detecting a dropped peer and should be done only if necessary.

    Default: True, must be set to False without Refer Support with Media Bypass · 

    EnableSessionTimer

    Specifies whether the session timer is enabled. Session timers are used to determine whether a particular session is still active.

    Note that even if this parameter is set to False, session timers can be applicable if the remote connection has session timer enabled. In such a case, the Mediation Server will reply to session timer probes from the remote entity.

    Default: False, should be true if your Gateway supports for dropped peer detection.

    Why use Media Bypass?

    Why go through all the trouble for media bypass. Well, if you have a lot of external users, they don’t need to double your bandwidth” for each call as it comes in and leaves your datacenter when you are using an external, internet accessible SIP trunk provider. The main benefit is reduced bandwidth (to and from traffic to the mediation server) and greater mediation server scalability

    This is a great blog article on Lync Server 2010 media bypass on VoIPNorm’s Unified Communications Blog:

    9 Media Bypass Scenarios on VoIPNorm’s Unified Communications Blog

    Media Bypass is actually pretty simple. Its all about matching the bypass ID that is generated when you enable Media Bypass. A unique ID is generated per network Region and for all sites within the region that do not have CAC applied to them. For those sites with WAN links that are using CAC a unique ID is generated.

    When a PSTN call is made the mediation server compares the Bypass ID of the clients subnet with that of the gateways subnet. If the two match you enable media bypass. If not, the media will flow through the mediation server. Now, if it is an inbound call the client will do the matching and if the ID’s match the media will flow directly from the gateway to the client. This has nothing to do with the subnet of the

    Important Note about SRTP Support

    For gateways that do not support SRTP you will need make a configuration change in the Lync Client through PowerShell to help support Media Bypass. If you do not change the encryption setting all calls will pass through the mediation server. You will also need to select the correct encryption level in the Trunk Configuration.This will mean that all PSTN media flowing to the gateway will be unencrypted. Something to keep in mind.

    set-csmediaconfiguration –identity global –encryptionlevel supportencryption

    For more information on the client setting see here:

    http://voipnorm.blogspot.com/2010/09/lync-client-2010-encryption-settings.html

    Read the rest of VOIPNorm’s article @> VoIPNorm’s Unified Communications Blog: Lync 2010 Media Bypass and CAC Part 2: Media Bypass You can read more on Media Bypass on TechNet@> http://technet.microsoft.com/en-us/library/gg398703.aspx Learn more about our Skype for Business (now Microsoft Teams) E5 PBX Services.

    Published on: .

    This post has matured and its content may no longer be relevant beyond historical reference. To see the most current information on a given topic, click on the associated category or tag.

    How can we help?

    Loading...

    Let's start a conversation

    location Agile IT Headquarters
    4660 La Jolla Village Drive #100
    San Diego, CA 92122

    telephone-icon + 1 (619) 292-0800 mail-icon Sean.L@Agileit.com

    Don’t want to wait for us to get back to you?