Microsoft SIP Processing Language
Sometimes you might like to modify the way that SIP messages are processed on Lync servers. Microsoft SIP Processing Language (MSPL) allows you to do just that. You can write a MSPL "message filter" to filter and route/reroute messages in Lync Server 2010 applications.
(HT: Ken Lasko for a really good example of using this feature to route calls that would fail without it)
What kinds of things can you do to a SIP message with MSPL? A full list of MSPL built-in functions can be found here, but just some examples are:
AddHeader – Adds a header to the current SIP message
Fork – Creates a forked copy of the current message with its request URI field set to the supplied URI string.
Respond – Generates a SIP response to the current request message with the supplied status code and reason phrase
Proxy Request/Response – Proxies the current SIP request or response.
Check out the additional references below.
MSPL Scripting Reference: http://msdn.microsoft.com/en-us/library/gg425301.aspx