The high level answer is it controls whether the soa portion of the sofia stack is used (http://sofia-sip.sourceforge.net/refdocs/soa/), disabling it would use an alternative implementation. Obviously there are differences between the implementations from what you've observed. I can't tell you exactly what though.

On 9 March 2015 at 16:29, Victor Chukalovskiy <victor.chukalovskiy@gmail.com> wrote:
Good day,

I find documentation regarding enable_soa param very scarce, so looking
for some clarifications here.

What exactly changes in FS behavior with enable_soa = false?

For example, I observe that with soa disabled, FS receiving "183" with
SDP on one leg substitutes it with plain "180 Ringing" on another leg.
This is not correct, but I'm not sure if it's a bug or an expected
outcome of disabling soa.

Thanks!!
-Victor

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