Sunday, May 1, 2016

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 !


1 comment:

  1. Hi Yogesh San,

    Thanks for the Post, encountered same issue today, but had to move a bit further, had to twek SRTP Settings in Trunk from *Required to Optional and tehn it started working :-)

    ReplyDelete