Added a line to set SRTP encryption. the default setting yealink_srtp_encryption was not setting properly to my T56a devices. I downloaded my config files and did not find an entry for srtp at all.
compared with the t54w template and it did have a srtp setting. So I pretty much stole the line from the T54w template and dumped it in here.
The T54w template is vastly superior to this one and this probably needs a rewrite to bring it in line.
Tested on my T56a and it at least gets the job done.
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