Blocking incoming calls from a PSTN number to Lync extension permanently (from AudioCodes PSTN Gateway)








Today we got a complaint from a user that he gets calls from a specific PSTN  number (+xxxxxxxxxx) repeatedly everyday and hence the user  wanted  to block any calls from that number.






Unfortunately, there were no much help in AudioCodes forum or Microsoft Forums related to this topics. Some Forums were suggesting to use MSPL script to block such calls those details are mentioned below, (you may go through if you find it interesting).




The MSPL script will block the calls from a particular number reaching the Lync end point.




https://gallery.technet.microsoft.com/MSPL-Blocking-Calls-on-e6d52de9 [ To download the MSPL script ]

https://blogs.technet.microsoft.com/uclobby/2014/07/31/calleridblock/ [ Step by step guide to use the MSPL Script on the Lync / SfB servers ]



https://blogs.technet.microsoft.com/uclobby/2016/04/01/missed-call-notification-when-the-call-is-blocked-by-calleridblock-mspl-script/  [ To block the Missed call notification ]





However, in our client environment since we were using several trusted applications, implementing these chances on a Critical application like  Lync servers would take several weeks (for tests and approvals).

So we were trying to find a way to block the  PSTN number at the PSTN Gateway end.

In order to replicate the issue, i tried to block all the calls to my Lync  extension from my mobile phone number.  So, first i tried couple of manipulations like creating a Rule in the Gateway such that the calls from a Number to the user's extension are forwarded to Trunk Group #  20 (which is not available in the Gateway). However the calls from my mobile number were still hitting my Lync extension (not sure how it gets a different route though).

So, i worked with my colleague (Will Talbot) on this topic. He suggested  to create a Rule for Destination Number Tel -->IP in the AudioCodes gateway.

Logged in to the AudioCodes  PSTN Gateway.

 Configuration section --> VOIP  -->   GW and IP to IP --> Manipulations --> Destination Number Tel to IP section.

The Rule my colleague (Will Talbot) suggested was to strip all the digits and add athe prefix as all 0's. We tried the rule and test it.

It worked immediately !! All calls from my mobile number to my Lync Extension were blocked successfully.  So I followed the same steps in order to block the annoying calls from the actual PSTN number to the User's Lync extension :-)


Hope this post is  useful for someone who is struggling to block all calls from particular (annoying) PSTN number to a Lync Extension.

AudioCodes and Lync Issues (488 : Invalid Incoming Gateway SDP)

Hello Everybody,

Today I just completed fixing an Lync server 2013 / Skype for Business 2015  and AudioCodes related issue and I am happy to share this experience so that it would help someone in future !

Issue:

Users are  not able to receive inbound calls from the PSTN to their Lync Extension. For this same customer we did the Lync Enterprise Voice project few years ago. The calls were working fine for years, but the customer complained that the calls started failing recently. 

Error: From the Gateway logs we got the following message. It looks like the Mediation server is  rejecting the SIP request.

SIP/2.0 488 Invalid incoming Gateway SDP: Gateway did not offer SRTP Keys which is required by Mediation Server.

Troubleshooting:

Since the Error had SRTP Keys, I first doubted it to be  a certificate issue. Because normally in a branch site there are possibility that the administrators not renewing the certificates once it is expired.

Checked  the Gateway certificates for its validity,  and found that the certificate was valid for another 200 days.

So tried to assign the extension of test account to my account, started testing and collected the Gateway logs.

On checking the SIP error message from the Gateway logs it was clear that the Mediation server is rejecting the connection because it is expecting SRTP keys from the Gateway. Check the SIP Message  Flow diagram below.

SRTP is used for the Media. So checked the Media Security configuration on the AudioCodes Gateway.

Logged in to the AudioCodes Gateway.  Configuration (Full) à  VoIP à Media à  Media Security Page.

The setting the Media Security was set to Disable.  So selected the DropDown box and then Set the option to Enable and did a Gateway Reset (in AudioCodes - Reset is required when you make changes to the Gateway Configuration. It is like Rebooting the Gateway for the new Configuration changes to take effect).

Once the Gateway came back online, I tried to make some test calls and it worked fine. I am providing the SIP ladder diagram of the working scenario below.

Thank you for reading this post and hope it was helpful !