“The odd call drops” of the Mediation Server

Nice findings in the article – very relevant for all Lync/S4B installations that includes one or more voice gateways.

y0av. With a zero.

I had a very annoying issue lately when an installation of a new gateway resolved in some calls (specifically to US numbers) dropped by the Skype for Business mediation server saying “A call to a PSTN number failed due to non availability of gateways.

The cause, according to the mediation server, was that “All gateways available for this call are marked as down“, and the resolution, surprisingly, was to “Verify that these gateways are up and can respond to calls.”

It seemed funny, because all other calls were successful, I have not exhausted the available PRI channels I had, the gateway didn’t seem to lose connectivity for a split second and SIP options are accepted and replied to on both ends.

Looking further at the Lync Monitoring Reports, I noticed the following:

Reported by Client
12000; reason=”Routes available for this request but no available gateway…

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iOS 9 and Lync Mobile 2013 Sign-In Issue

Just a Lync Guy


Today (9/16) Apple released iOS 9 for iPhone/iPad devices which introduce a list of new features and enhancements around security as well.


Following users feedback, a sign-in issue was discovered with iOS 9 and Lync 2013 Mobile clients which effect users that have different settings for their region and language one the iOS device, meaning that heir region settings is set to a different language then the iOS language.

For those who have different settings, the following error message would appear:



The current workaround for now is to change the iOS language to the match the region settings (or vice-versa) until Microsoft will address the issues with upcoming update or with the next SfB Mobile client version.

Additional Information:

  • Microsoft also released a KB article describing the problem
  • A great blog describing the root cause analysis you can find here
  • Another great blog post from Mika (

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Lync Reverse Proxy, create CSR in TMG

Nice blog post on creating Lync Reverse Proxy Certificate Request from TMG.

Chad McGreanor's Blog

Below are the steps to create a standalone certificate request from the TMG 2010 server in order to generate a CSR for a Public CA.

  1. Open Certificate MMC
  2. Expand Personal > Certificates
  3. Right – Click Certificates then All Tasks then Advanced Operations Then Create Custom Request
  4. Select Next
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  6. Select Proceed without enrollment policy
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  8. Select No template legacy Key
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  10. Select Properties
  11. Enter a friendly name
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  13. On the Subject tab enter the Common Name and Alternative names
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  15. On the extensions tab under Key Usage choose Digital Signature and Key encipherment
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  17. Under extended key usage choose Server Authentication and Client Authentication
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  19. Under the private key tab under key options choose key size and select 2048 and select private key exportable
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  21. Under Key type choose Exchange and ensure that the key size above is set to 2048
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  23. Select OK, Choose path to save and provide the CSR to a Public CA and then import…

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