Hi,
In order to provide SIP Gateway support for TLS you need to use the "SPSERVICES" featureset in the IOS.
Cisco have also pulled support for your IOS version due to multiple bugs
You should upgrade 15.0.1.M7 -SPSERVICES
You will need 128M of flash & 512 M DRAM
HTH
Alex
Regards,
Alex.
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