setup an Asterisk as SIP Gateway for Lync Server

we have a Lync server runing, we need to ad sip trunks but the provider does not support TLS or TCP, so we need an Asterisk to work as a gateway this asterisk can recieve multiple trunks and can be forwarede to multiple Lync servers. the freelancer will have to guive us a step by step document of how to add more trunks to the asterisk and how to setup this trunks in to the lync server.