Conference Requests sent to other companies who have Lync are failing

Greetings! We have Lync 2013, patched to the latest CU's. We have a particular company/vendor/partner that also has Lync, when our users send their users a Lync meeting request, the end user is invariably unable to connect to the Lync conference. Our user has opened a ticket requesting that I add "?SL=1" to the end of the meeting notice. This is a known workaround for people who experience this issue, allowing them to use the web client instead of the Lync desktop client, but I'm not comfortable that adding this to all our meeting requests is the correct solution. I notice that we don't have any issues connecting to other companies' Lync meetings, so my first thought is that something is not configured correctly, or a patch/cu is missing on their end.

So, I was wondering if anyone else out there has had similar experiences with this issue and what the solution has been. I have already suggested to the users that they ask the recipients to type this at the end of the URL themselves, which was of course met with derision.

Here are our current conferencing settings:

Identity                             : Global
TrustedCACerts                       : {}
CrossDomainAuthorizationList         : {}
MaxGroupSizeToExpand                 : 100
EnableGroupExpansion                 : True
UseWindowsAuth                       : Negotiate
UseCertificateAuth                   : True
UsePinAuth                           : True
UseDomainAuthInLWA                   : True
AllowAnonymousAccessToLWAConference  : True
EnableCertChainDownload              : True
InferCertChainFromSSL                : True
CASigningKeyLength                   : 2048
MaxCSRKeySize                        : 16384
MinCSRKeySize                        : 1024
MaxValidityPeriodHours               : 8760
MinValidityPeriodHours               : 8
DefaultValidityPeriodHours           : 4320
MACResolverUrl                       :
SecondaryLocationSourceUrl           :
ShowJoinUsingLegacyClientLink        : False
ShowDownloadCommunicatorAttendeeLink : True
AutoLaunchLyncWebAccess              : True
ShowAlternateJoinOptionsExpanded     : False
UseWsFedPassiveAuth                  : False
WsFedPassiveMetadataUri              :
AllowExternalAuthentication          : True

Please let me know if you need more information. Th

May 15th, 2015 11:36am

You should check you public dns settings. Have you create all necesarry srv records like _sipfederationtls._tcp.yourd
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May 15th, 2015 4:12pm

Yes, we have. Conference calls are working with all other entities, just this one particular company that has Lync. We are fully federated with several companies, we have multiple partners and suppliers as well with their own Lync environments that we have no issues with.

Good question, though. Thanks!

May 15th, 2015 4:23pm

Maybe something with the public certificate (revokation list) or with the dns from the other partner.

I think a trace from the partner of the Lync client could help.

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May 16th, 2015 2:58am

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